Chapter 1 Introduction

Chapter 1

Introduction

The introductory chapter presents an overview of the developments in the area of

preceramic polymers with a special reference to polysilahydrocarbons and

polyborosiloxanes. A brief account of end-uses of preceramic polymers is given.

The chapter concludes with the objective and scope of the present investigation.

2 Chapter 1

he field of polymer science forms one of the major areas of molecular and

materials science. This field impinges on nearly every aspect of modern

life, from electronics technology, to medicine, to the wide range of fibers,

films, elastomers and structural materials on which everyone depends. Most of

these polymers are organic materials where the long-chain backbones consist

mainly of carbon atoms linked together or separated by heteroatoms such as

oxygen or nitrogen. Organic polymers are derived from petroleum and less

frequently from plants, animals and microorganisms. Hence, they are generally

accessible in large quantities and at moderate cost.

In spite of the widespread importance of organic polymers, attention is

being focused increasingly towards polymers that contain inorganic elements as well

as organic units in their backbone. Such polymers, referred to as inorganic or

organometallic polymers, overcome many of the disadvantages of organic

polymers. Most of the organic polymers react with oxygen or ozone over a long

period of time and lose their advantageous properties. Organic polymers, in

general, have poor thermooxidative stability and undergo degradation when

exposed to ultraviolet or gamma radiation. On the other hand, inorganic and

organometallic polymers possess excellent high temperature properties, thermo-

oxidative stability and radiation resistance. Other advantages include fire resistance,

chemical inertness and resistance to free radical cleavage.1

The polymers which contain only inorganic elements in the polymer

backbone are called “ inorganic polymers”, whereas the ones which contain

metallic elements along with organic units in their backbone are called

“organometallic polymers”. Truly speaking, there appears to be no clear-cut

demarcation between these two categories and quite often they are used

interchangeably.

Inorganic and organometallic polymers find wide range of applications as

high temperature coatings, thermal protective systems, matrix resins, high

temperature elastomers and precursors for ceramics, due to their excellent high

temperature properties and thermooxidative stability. In the last three decades

considerable attention is paid towards using these polymers as precursors for

T

Introduction 3

ceramics. Inorganic and organometallic polymers capable of giving high ceramic

residue (50% or above) on heat treatment in inert atmosphere are called

”preceramic polymers”.

Following the first report by Yajima et al.2 that disclosed the use of polycarbosilane derived from polydimethylsilane as a precursor for SiC fiber, wide variety of inorganic and organometallic polymers have been reported as precursors for ceramics. Polysilanes, polycarbosilanes, polysilahydrocarbons, polycarbosilazanes, polysiloxanes, polyborazines, polycarborane-siloxanes, borosiloxanes etc. have all been explored as precursors for ceramics. The developments in the area of preceramic polymers have been discussed in various reviews.3-9 In view of the voluminous literature available on this topic, it is rather difficult to discuss all the developments in detail. Hence, the introductory chapter of the present thesis provides only an overview of the important developments in the area of preceramic polymers. While presenting the literature, emphasis is laid on silicon, and silicon and boron containing polymers as the thesis deals with polysilahydrocarbons and borosiloxanes.

1.1 Silicon containing polymers 1.1.1 Polysilanes

Polydiorganosilylenes commonly referred to as polysilanes is relatively a

new class of inorganic polymers having an all silicon backbone. The first

polysilane was probably prepared by Kipping10,11 in the early 1920s by the

dechlorination of diphenyldichlorosilane (DPDCS) using sodium. But it was

infusible and insoluble. Bukhard12 synthesized polydimethylsilane (PDMS) from

dimethyldichlorosilane (DMDCS), using a similar procedure, which also suffered

from the same problem as in the case of polydiphenylsilane. This led to the

neglect of this field until Yajima and coworkers2 in 1975 reported the conversion of

intractable PDMS by heat treating it in an autoclave to a processable

polycarbosilane.

West and coworkers3,13-17 prepared soluble copolymers from

methylphenyldichlorosilane (MPDCS) and DMDCS by Wurtz reaction with sodium.

A copolymer obtained with an equimolar ratio of MPDCS and DMDCS is called

4 Chapter 1

“polysilastyrene” (Structure 1) due to its structural resemblance with polystyrene

and it exhibits a bimodal molecular weight distribution with a molecular weight

( WM ) of ~ 50,000.

where x/y =1

Structure 1 Alkali metals such as sodium and potassium are generally employed for

the dechlorination5 whereas lithium favors the formation of cyclic products. Use of

catalytic amount of crown ethers (18-crown-6 or 15-crown-5) along with sodium is

found to enhance the polymer yield and change the molecular weight distribution

from bimodal to monomodal.18-22

Polysilastyrene after crosslinking by UV irradiation gave ~30% ceramic

residue on pyrolysis and the poor ceramic residue was attributed to incomplete

crosslinking.15 Schilling et al.23-25 described the synthesis of vinyl-functionalized

polysilane by reacting methylvinyldichlorosilane (MVDCS), DMDCS and

trimethylchlorosilane (TMCS) with sodium in an inert solvent and also the

formation of polysilanes containing Si-H and Si-vinyl functional groups by

dechlorinating methyldichlorosilane (MDCS) with MVDCS and TMCS in presence

of sodium in toluene/THF mixture.

Functionalization of polysilanes drastically influences their solubility, Tg,

cure kinetics and ceramic residue.26-28 In recent years, polymethylsilane,

synthesized by dechlorination of MDCS has been studied extensively as a

promising precursor to SiC8,29-52 because of its ideal stoichiometry. However,

polymethylsilane gives lower ceramic yield on pyrolysis. Several authors focused

on the role of Si-H bonds in polymethylsilane for improving the final ceramic yield

by promoting crosslinking.8,38-46 In order to improve the ceramic yield,

polymethylsilane-based precursors were used in presence of crosslinking agents

nyx

CH3CH3

C6H5CH3

SiSi

Introduction 5

such as boron containing catalysts31,35,36,41,48,49 and metallocene26 which enhanced

the precursor processability and ceramic yield. When metallocene was used as a

catalyst, long reaction time and high pressure were required.

Iseki et al.52 reported a reflux heat treatment as a simple and effective

procedure to enhance the ceramic yield without using catalysts or high pressure.

The reflux process is an effective way to convert linear Si-Si units into CSiSi3 units

prior to carrying out Kumada’s rearrangement.53 Gon et al.54 reported a method for

enhancing the molecular weight of polymethylsilane at 70°C by carrying out the

synthesis in the presence of polyborazine.

Polymethylsilane is, however, not sufficiently oxygen stable and is often

flammable in air at room temperature.47 In addition, polymethylsilane-derived

ceramics contain considerable amount of silicon. Iseki et al.55,56 had overcome

these problems by using poly(methylsilane-dimethylsilane) copolymers in place of

polymethylsilane. These copolymers serve as matrix resins for ceramic matrix

composites (CMCs).

Radiation curing of polymethylsilane is now considered as an industrially

viable method to produce high heat resistant SiC fibers with low oxygen content.

γ-Ray radiation curing studies of polymethylsilane and poly(methylsilane-

dimethylsilane) precursor with improved ceramic yield were reported by

Iseki et al.56

Apart from the classical Wurtz reaction, several novel electrochemical57-62

and ultrasonic methods21,63-65 have also been reported for the synthesis of

polysilanes. Of late, synthesis of newer polysilanes and their characterization have

been reported.66-76 Recently, a room temperature synthesis of polysilanes with

high yield (50 to 83%) was reported by Holder et al.77

1.1.2 Polycarbosilanes

Polymers with backbone comprising of silicon and carbon are termed

“polycarbosilanes”. Yajima et al.2,78-80 in their pioneering work, prepared

polycarbosilane by heat treatment of dodecamethylcyclohexasilane (Me2Si)6 or

6 Chapter 1

polydimethylsilane in an autoclave in argon atmosphere at temperatures above

400°C under pressure (Scheme 1.1)

Scheme 1.1. Yajima's process

Yajima et al.81 studied the use of a catalyst, viz., borodiphenylsiloxane for

the thermal conversion of PDMS to polycarbosilane at atmospheric pressure at

350°C. Habel et al.82 reported the use of poly(borodiphenylsiloxane) for converting

polysilane containing methyl and phenyl groups to boron containing

polycarbosilane. Polycarbosilanes were also prepared by ring opening

polymerization of 1,3-disilacyclobutane83 and substituted 1,3-disilacyclo-

butanes83,84 using chloroplatinic acid as catalyst. Poly(diethylsilmethylene) having

molecular weight ( nM ) of 2,50,000 was prepared by the ring opening

polymerization of 1,1,3,3-tetramethyl-1,3-disilacyclobutane with platinum

catalyst.85 This polymer is thermally stable up to 600°C in inert atmosphere, but

readily decomposes at 200°C in presence of air.

SiClCH3

ClCH3

NaNa

(C6H5)2SiCl2Na

Si

CH3

CH3

n

Si

CH3

CH3

n

Si Si SiSi

CH3 CH3 CH3

CH3CH3CH3 C6H5

C6H5

n

Si C

CH3 H

H H n

Si C Si C n n

autoclaveautoclave (C6H5)2SiOBO2 n

PCS-I PCS-I PCS-I I II

Introduction 7

Seyferth and Lang86 synthesized polycarbosilanes with regularly

substituted pendant Si-vinyl groups by the ring opening polymerization of 1-vinyl-

1-silacyclobutane in tetrahydrofuran (THF) and hexamethyl phosphoramide using

butyllithium as a reducing agent. Polymers were obtained in 60-88% yield and the

molecular weight ranges from 6,000 to 11,000. They are stable up to 400°C and

undergo decomposition above 450°C.

Pillot et al.87 explored the reductive coupling of dichlorodisilylmethane with

alkali metal as a means of preparing polycarbosilane. Polycarbosilanes were also

obtained by the dehalogenation of diorganodichlorosilanes with dihalomethanes

using alkali metals.88

Whitmarsh and Interrante89 studied the Grignard coupling of

chloromethyltrichlorosilane (ClCH2SiCl3) by reacting with magnesium in

diethylether. A branched polycarbosilane was formed when the chloroderivative

was reduced with LiAlH4. Habel et al.90,91 reported the reduction of halogenated

poly(methylphenylsilmethylene) and poly(diphenylsilmethylene) with LiAlH4 to

obtain poly(hydridopolycarbosilane)s.

Schilling and co-workers29,92,93 synthesized branched polycarbosilanes

from a vinyl-containing chlorosilane monomer. When dechlorination of MVDCS

was carried out in presence of TMCS using potassium in THF,

tetra(trimethylsilylated) compound was obtained as the major product.92 This

suggests that vinyl group takes part in the polymerization. Schilling et al.29,93

synthesized branched polycarbosilanes by dechlorinating MVDCS with potassium

in THF in presence of DMDCS or MDCS and TMCS.

Polycarbosilanes with ethylenic and acetylinic functionality were prepared

from poly(dichlorosilmethylene)s.94,95 Poly(silaacetylene)s were prepared by

reacting dilithioacetylene with diorganodichlorosilanes (RR'SiCl2) [where R = Me

or Ph] or with 1,2-dichlorodisilane (ClMe2Si-SiMe2Cl).95 A silylenediacetylene

polymer of high molecular weight was prepared by Maghsoodi and Barton96

starting from hexachlorobutadiene. Habel et al.97 reported the synthesis of

poly(alkynylsilmethylene) containing the repeating unit, -SiR2CH2-, where

8 Chapter 1

R= -C≡CH, -C≡C(CH2)nCH3 or -C≡C-C6H5. Uhlig98 reviewed the synthesis of new

organosilicon polymers using silyl triflate intermediates. Proto-dephenylation of

phenylated polysilanes as well as poly(silylenemethylene)s by triflic acid gave new

functionalized compounds. Thermally stable polysilylenemethylenes with siloxane

crosslinking moieties were successfully synthesized by Ogawa et al.99 with Tg

ranging from 15 to 20°C.

A wide range of new poly(silylenemethylene)s100-102 of the type

[SiRR’CH2]m were prepared and their conversion to ceramic material was studied

in detail. Kwak and Masuda103 found that the polymerization of p-(dimethylsilyl)-

phenylacetylene in toluene at 25°C and 80°C using Rh1(PPh3) catalyst afforded

highly regio- and stereoregular poly(dimethylsilylenephenylene-vinylene)s.

Amoros et al.104 studied the reaction of poly(dimethylsilane) and

poly(dimethylcarbosilane) with bis(cyclopentadienyl)M dichloride Cp2MCl2 (M= Ti,

Zr, Hf) complexes to obtain precursors for SiC ceramics. Tsumura and Iwahara105

developed crosslinked polycarbosilanes with excellent mechanical properties by

hydrosilylation curing of multi-functional vinylsilanes with hydrosilanes. Chemically

modified polycarbosilanes containing organofluoric groups106 and Si-Al-C-O

linkages107 with improved ceramic yield, were synthesized by Okuzaki et al.106,107

by reacting polycarbosilane with fluoric acid and aluminium triisopropoxide

respectively. Cao et al.108 obtained dry-spinnable polycarbosilane by reacting the

polycarbosilane, prepared by Yajima’s process, with 1 wt% of polyborazine at

300°C for 1 h. A hyperbranched polycarbosilane of the type [R3SiCH2–]x-

[–SiR2CH2–]y [–SiR(CH2–)1.5]z [–Si(CH2–)2] was prepared by Interrante et al.109,110

for end-use as an inorganic/organic hybrid material.

1.1.3 Polysilahydrocarbons

Polymers containing two or more carbon atoms between silicon atoms are

referred111 to as “polysilahydrocarbons”. They were synthesized through the

dechlorination of diorganodichlorosilanes in presence of vinyl or diene

monomers111-115 (Scheme 1.2). Schilling et al.111 synthesized polysilahydro-

carbons by dechlorinating diorganodichlorosilane in presence of styrene or

isoprene.

Introduction 9

Scheme 1.2. Synthesis of polysilahydrocarbons

Van Aefferden et al.112 and Packirisamy et al.113-115 synthesized

polysilahydrocarbons by reacting DMDCS and styrene under dechlorination

conditions. They observed that the copolymers contain alternating units of disilyl

and styryl in the polymer backbone. Packirisamy et al.113-121 studied in detail the

effect of monomer feed ratio and reactivity of diorganodichlorosilanes on the

microstructure and mechanism of formation of polysilahydrocarbons through the

dechlorination of diorganodichlorosilanes in presence of styrene. In the

copolymers synthesized from styrene and DMDCS, disilyl and styryl/oligostyryl

units alternate with each other for the monomer feed ratios (styrene:DMDCS)

0.5:1, 1:1 and 1.5:1. With further increase in concentration of styrene, i.e., for the

monomer feed ratio of 3:1, no disilyl linkage was observed and the repeating units

mainly consisted of monsilyl linkages separated by oligostyryl units. However, for

styrene-MPDCS system, disilyl linkages separated by oligostyryl units were

observed even when the monomer feed ratio (styrene:MPDCS) was 5:1. This is

attributed to the higher reactivity of MPDCS compared to that of DMDCS.

Microstructural analysis of polysilahydrocarbons supported the conclusion that

disilyl reaction intermediates mediate the polymerization. When styrene is present

in large excess, styryl reaction intermediates mediate the polymerization resulting

in the formation of monosilyl linkages separated by oligostyryl units. A generalized

structure of the polysilahydrocarbon synthesized from MPDCS and styrene is

given in structure 2.

MeSiHCl2

K/THF

Isoprene

K/THF

Si CH2 CH

PhMe

H n

Si CHCCH2 CH2

MeH

Me

n

PhCH2 CH

10 Chapter 1

Structure 2

Ambadas et al.122,123 synthesized a novel polysilahydrocarbon from a

single source precursor. Dechlorination of 1,2-bis(chlorodimethylsilyl)ethane

[BCDMSE] in presence of potassium resulted in the formation of a polymer,

poly(tetramethyldisilyleneethylene) (Structure 3) whereas no polymer was

obtained when sodium was used for the dechlorination. This was attributed to the

low reactivity of this monomer under dechlorination conditions. Interestingly, this

monomer underwent dechlorination in presence of styrene.

Structure 3

Thus, it is obvious that depending on the reactivity of

diorganodichlorosilane, either disilyl or styryl reaction intermediates mediate the

polymerization. A typical structure of the polysilahydrocarbon synthesized from

BCDMSE and styrene in presence of Na/18-crown-6 is given below (Strucure 4).

Structure 4

Packirisamy et al.117 synthesized crosslinked polysilahydrocarbons by

reacting MVDCS with styrene under dechlorination conditions. During

dechlorination, vinyl group of MVDCS participates in the polymerization resulting

a

CH CH2

CH CH

b n

2

Ph

Si Si

Me

Me

Ph

Si Si

Me

MePh

Ph Ph

Ph

Ph

C H2C

H

Me

MeMe

SiCH2CH2Si

Men

Me

Me Me

Si CH 2 CH 2 Si

Me n

Introduction 11

in the formation of crosslinks. A typical structure of poly(methylvinylsilylene-co-

styrene) is given below (Structure 5).

Structure 5

Polysilahydrocarbons have poor thermal stability and give very poor

ceramic residue (<20%). Sartori et al.124,125 explored the possibility of converting

polysilahydrocarbon synthesized from DMDCS and styrene to thermally stable

polycarbosilane by heat treating the polysilahydrocarbons at 385°C in an

unconfined atmosphere under the flow of argon.

Packirisamy et al.115,126 studied the microstructure, thermal stability and

ceramic conversion of polycarbosilanes obtained by heat treatment of

polysilahydrocarbons in a partially confined environment. It was observed that the

incorporation of small amount (<10 mole%) of methylphenylsilyl units in the

copolymer containing dimethylsilyl and styryl units drastically improved the thermal

stability and ceramic residue of polycarbosilane. This has been attributed to the

phenylene insertion reaction taking place during heat treatment. A typical structure

of the heat-treated polysilahydrocarbon is given below (Structure 6).

Structure 6

nx

Si Si

Me

Me

Me

Me

Si Si

Me

Si

Me Me

H H

CH 2

CH 2

Ph

CHSi

nMeCH

CH2

Si

Me

a

CH

Si

Me

CH

CH2

CH2

xSi

Meb

CH

CH

Ph

CH2

CH2

12 Chapter 1

In the present investigation, thermal degradation kinetics of

polysilahydrocarbons, synthesized by Ambadas122 and the polycarbosilanes

derived from them,126 and the end-use of polysilahydrocarbons as atomic oxygen

resistant coatings for low earth orbit space structures have been studied and they

form the basis for the chapters 3.6 and 3.7.

Polysilahydrocarbons serve as potential candidates for liquid

lubricants.127 This advanced space lubrication systems replace the currently

employed perfluoropolyalkylethers, which promote metal corrosion and undergo

degradation under boundary lubrication conditions. The properties of these

polysilahydrocarbons can be tailored by varying the alkyl substituent.

Corriu et al.128-130 described the preparation of linear poly(silylethylene)

from vinyl hydrogenosilane using platinum in charcoal as a catalyst. Catalytic

hydrosilylation of ethynylsilanes [(R2HSiC≡CH), where R=Me, Et or Ph] with

chloroplatinic acid was studied as a means of preparing polymers with ethylenic

functional moieties in the backbone.

Wu and Interrante131 prepared poly(silethylene)s by the ring opening

polymerization of 1,1,3,3-tetrachloro-1,3-dimethyl-1,3-disilacyclobutane using

chloroplatinic acid or platinumdivinyltetramethyldisiloxane complex as a catalyst.

A new polysilahydrocarbon, viz., chemically crosslinked polysilastyrene

was prepared by Krishnan et al.132 through the dechlorination of a monomer

mixture containing DMDCS and MPDCS in presence of divinylbenzene. The

crosslinked polymer on pyrolysis at 1500°C gave β-SiC.

In recent years, polysilarylenes and polycarbosilarylenes with excellent

thermal stability have been reported.133-135

1.1.4 Polysilazanes and polycarbosilazanes

Polymers with silicon-nitrogen linkages in their backbone are termed

”polysilazanes”.8,136,137 They are generally prepared either by ammonolysis or

aminolysis of organochlorosilanes.

Introduction 13

Verbeek,138,139 in his pioneering work, synthesized polysilazanes by

aminolysis of chlorosilane monomers. Polysilazanes were prepared in a two step

process involving amination of trichloromethylsilane followed by the thermal

condensation of the product tris(N-methylamino)methylsilane.138-140 Aminolysis of

DMDCS and methylamine following a similar procedure as above was carried out

by Winter et al.141 Seyferth and Wisemann142 reported the synthesis of

N-methylpolysilazane from methylamine and dichlorosilanes.

A perhydropolysilazane was synthesized by passing ammonia gas

through a pyridine-dichlorosilane adduct.143 Polysilazanes were also prepared by

reacting trichlorosilane with hexamethyldisilazane [(Me3Si)2NH].4

Seyferth et al.144,145 described in detail the ammonolysis of organodichlorosilanes.

Ammonolysis of MeHSiCl2 resulted in a cyclic silazane (MeSiHNH)3-4 and a linear

polymer (Scheme 1.3).

Scheme 1.3. Synthesis of polysilazane Seyferth et al.144 also reported the preparation of polysilazane free from

carbon by reacting dichlorosilane (SiH2Cl2) with gaseous ammonia in polar

solvents like dichloromethane or diethyl ether.

Burns et al.146 prepared polysilazanes by the ring opening polymerization

of cyclic silazanes prepared by ammonolysis and co-ammonolysis method. In the

first route silacyclobutasilazane was equilibrated with chlorosilane to give a

mixture of chloro end-blocked silazanes, which was ammonolyzed to obtain the

desired substituted silacyclobutasilazane. In the second route, a mixture of

1,1-dichloro-1-silacyclobutane and a chlorosilane was co-ammonolyzed directly.

Ammonolysis of a mixture of MeHSiCl2 and MVDCS or allyldichlorosilane afforded

vinyl- or allyl-functionalized polysilazane.145 The advantage of having a vinyl or

allyl group is that it provides -C=C- functionality which can be crosslinked via.

hydrosilylation reaction.

(MeSiHNH)x MeSiHCl 2 NH 3 Et 2 O/0°C

(ii)CH I 3 (i) KH THF/RT

Polymer

14 Chapter 1

Xu et al.147 synthesized a new kind of polysilazane precursor containing

linear-cyclic structure from the dilithium chloride condensation reaction of

hexamethylcyclotrisilazane lithium salts and 1,3-dichlorotetraorganodisilazanes

[(ClR1R2Si)2NH]. Bao et al.148 prepared a copolysilane-cyclodisilazane precursor

which was then heated to 1650°C to obtain SiC and Si3N4. Kleebe et al.149

prepared different liquid polysilazanes with tailored molecular structures by

ammonolysis of functionalized chlorosilanes. Pyrolysis of the polysilazanes

resulted in the formation of amorphous SiCN ceramics.

Hydrosilylation between 1,1,3,3-tetramethyldisilazane and 1,3-divinyl-

1,1,3,3-tetramethyldisilazane occurs rapidly at 90°C in the presence of Karstedt's

catalyst (Pt-divinyltetramethyldisiloxane) to give large macrocyclic products.

Similar observation was made by Son and Rasul150 when trimethylsilylated or

methylated derivative of 1,3-divinyl-1,1,3,3-tetramethyldisilazane was reacted with

1,1,3,3-tetramethyldisilazane.

Trassl et al.151 prepared polyvinylsilazane, a precursor for SiCN ceramics,

by ammonolysis of functionalized chlorosilanes. Pyrolysis under inert atmosphere

at 1000°C led to the formation of an amorphous SiCN ceramic. A polymeric

precursor for the Si3N4-SiC-Y2O3 ceramic system was synthesized by

Sawai et al.152 by block copolymerization of perhydropolysilazane with hydroxy-

polycarbosilane, followed by chemical modification with yttrium methoxide.

Polycarbosilazanes have alternating silicon, carbon and nitrogen units in

their backbone. A polycarbosilazane was synthesized by heating a polysilazane

obtained from the sodium reduction of a mixture of DMDCS and l,3-dichloro-l,3-

dimethyldisilazane.153 This polymer on pyrolysis gave SiC-Si3N4 mixed non-oxide

ceramics.

1.1.5 Polysilylcarbodiimides

Kienzle et al.154 developed a new class of silicon and nitrogen containing

polymers called “polysilylcarbodiimides”. These polymers were prepared by

reacting organochlorosilane with cyanamide. Polysilylcarbodiimides were also

Introduction 15

prepared by reacting chlorosilanes with bis(trimethylsilyl)carbodiimide.155 These

polysilylcarbodiimides can be transformed into amorphous silicon carbonitride

ceramics with about 65% ceramic yield, by pyrolyzing them in an inert atmosphere

at 1100°C. The advantage with these polymers is that no prior crosslinking is

required before pyrolysis.

1.1.6 Polysiloxanes and polysilsesquioxanes

Polysiloxanes are unique among inorganic polymers.1 They are the most

studied and the most important ones due to their commercial significance. The

Si-O backbone of this class of polymers endows it with a variety of fascinating

properties. The high strength of Si-O bonds is responsible for high thermal stability

of polysiloxanes.

Diorganodichlorosilanes obtained by Rochow’s process, that starts from

elemental silicon, are used for the synthesis of polysiloxanes. This compound with

the general formula R2SiCl2, can be used for the preparation of a wide variety of

polymers having both organic and inorganic character. On hydrolysis, R2SiCl2

gives dihydroxy structures, which readily condense to give basic repeating units

(Scheme 1.4). The nature of the product mostly depends on reaction conditions.

where R = alkyl or aryl Scheme 1.4. Synthesis of polysiloxane

Polysilsesquioxane is an example for highly crosslinked organic-inorganic

hybrid material. Its inorganic cage frame work is made up of silicon and has the

formula of (SiO1.5)n where n = 8, 10 or 12.156,157 This inorganic cage is externally

covered by organic substituents, which enhance their solubility in organic solvents.

They are prepared by hydrolytic condensation (sol-gel process) of trifunctional

organosilicon monomers.158

Si + R2SiCl22RClH2O

Si

R

nO

R

16 Chapter 1

Among various silsesquioxanes, the octaphenylsilsesquioxane (PhSiO1.5)8

(Structure 7), decaphenylsilsesquioxane (PhSiO1.5)10 and dodecaphenyl-

silsesquioxane (PhSiO1.5)12 systems are the most interesting ones because of

their high temperature stability.

Structure 7

Polysiloxanes and silsesquioxane sol-gels were reported as precursors to

ceramics such as siliconoxynitride,159 siliconoxycarbide160-162 and SiC163,164 and

black glass matrices for composite materials.164-166 Since 1987 attempts have

been made to use siloxane polymers as precursors for ceramics and as binders

for sintering of SiC monoliths.167 The properties of these resins which make them

attractive as binders are the following: i) facile synthesis, ii) thermal and aerobic

stability for subsequent processing, iii) compatibility with the ceramic powder, iv)

decomposition into stable ceramics comprising of SiC and C at temperatures

below those required for sintering of SiC (~ 2000°C) and v) sufficient char yield

thereby minimizing the amount of volatiles evolved in the pyrolysis.163,168

White et al.160 reported that heating (PhSiO1.5)x gels to 1500°C produced a

partially crystalline mixture of β-SiC, SiO2 and C as detected by XRD and IR.

Babonneau et al.169 reported NMR evidence for the formation of β-SiC from

(Me2SiO)x (SiO2)1-x.

Porous ceramics with open or closed porosity combine various interesting

properties, like low density, low thermal conductivity and high specific strength.170

Therefore, they are of interest for an increasing number of applications

Si

O

SiOSi

O

OSi

Si O

O

SiO

Si

O

SiO

O

O

O

R

R

R

R

R

R

R

R

where R=Ph

Introduction 17

(e.g., thermal insulation, catalyst support, lightweight structures). Siliconoxy-

carbide ceramics are favorable candidates to meet these requirements. They are

commonly prepared by two techniques. One technique is based on the sol-gel

process171 and the other method uses preceramic polymers such as polysiloxanes

as starting materials. When polysiloxane is used the shrinkage in the 'green body',

the undesired feature of the polymers from the sol-gel process, is avoided. Yet

another advantage is that polysiloxanes are easily mouldable.172

A series of trimethylsilyl end-functionalized aliphatic hyperbranched

polymers were studied to template porosity in polymethylsilsesquioxane fi lms

prepared by heat treatment of a spin cast methylsilsesquioxane precursor.173 By

varying the extent of the functionalization, ceramic foams with controlled pore

sizes were obtained.

A number of polysiloxane resins filled with different oxide, carbide or

metallic powders were investigated as precursors for ceramics.174-180 Thin-walled

(wall thickness: 100–2000 µm) Si-O-C-N mono- and bilayered ceramic tubes were

obtained by centrifugal casting of a suspension of Si and SiC powders in

polyorganosiloxane/triethoxysilane solution.181 After centrifugal casting in a Teflon

tube with a rotational speed of 2000 rpm and subsequent crosslinking at 130°C

and 60 rpm, the tubes were pyrolyzed in argon or in nitrogen at 1400–1600°C.

Bilayered tubes with controlled variation of porosity were obtained by overcasting

the monolayer green tubes with a modified slurry composition.

Philipp182 evaluated polysiloxane formed by the controlled hydrolysis of

tetraethoxysilane (TEOS) as a binder for the formation of an oxide ceramic

compact. At high temperature, the oxide particles are held together via reaction

bonded silicates formed from SiO2 obtained from the pyrolysis of the precursor.

1.2 Boron containing polymers

The key developments in organosilicon chemistry led researchers to work

on novel synthetic approaches leading to the development of innumerable boron

containing polymers and to explore their end-uses in terms of technological

advantages offered by them. Boron forms a number of polymeric materials with

18 Chapter 1

many other elements involving particularly bonds of B with H, C, O, N and P. The

high bond energy of some of these bonds is responsible for their high temperature

stability. Majority of boron containing polymers are derived from borazine,

carborane and decaborane.9,183,184 A few polymers have also been synthesized

from vinylpentaborane and boric acid.

1.2.1 Polymers derived from borazines

A tractable polyborazine which can be used as a precursor for boron

nitride ceramic was first reported by Taniguchi et al.185 Later, Sneddon et al.186,187

synthesized a processable polyborazine (also known as polyborazylene) by the

thermolysis of liquid borazine in vacuum at 70°C (Scheme 1.5).

Scheme 1. 5. Synthesis of Polyborazylene

This polymer was obtained as a white powder in high yield (~90%). It has

molecular weight ( wM ) of 7,600 and has a branched structure. Polyborazylenes

serve as excellent precursors for boron nitride ceramics.188 Boron nitride was

obtained by heating this polymer in either argon or ammonia. Narula et al.189

synthesized poly(borazinylamine), by adding excess ammonia to cold toluene

solution of B-tris(dimethylamino)borazine [(Me2N)BNH]3. Kimura et al.190 studied the ammonolysis of B-tris(diethylamino)borazine in

liquid ammonia at room temperature and obtained a crystalline solid

B,B’,B”-triaminoborazine [(H2N.BNH)3]. This solid undergoes rapid deamination at

120°C forming a slightly soluble polymer. Synthesis of substituted borazines such as B-triamino-N-triphenyl-

borazine, B-triamino-N-trimethylborazine and B-trianiloborazine has also been

reported.191,192

B

N

B N

B

NH

H

H

H

H

H

B

N

B N

B

NH

H

H

H

70°C

n

Introduction 19

Paine et al.193,194 and Paciorek et al.195,196 prepared poly(borazinylamine)

by reacting B,B’,B’’-trichloroborazine with hexamethyldisilazane in ether medium

or in a hydrocarbon solvent. Pyrolysis of this polymer in vacuum at 1200°C

resulted in the formation of turbostatic hexagonal boron nitride [(h)-BN].

Maya197,198 synthesized polyaminoborazines through the condensation of

triethylborane or tris(dimethylamino)borane with polyfunctional amines such as

4,4'-methylenedipyrazole, 1,2-phenylenediamine, 3,3-diaminobenzidine and

diethylenetriamine. These polymers were used as precursor for boroncarbonitride

(BCN) ceramics.

Sneddon et al.199-201 prepared poly(β-vinylborazine) by solution

polymerization of β-vinylborazine with a free radical initiator azobisisobutyronitrile

(AIBN). β-Vinylborazine was obtained through the reaction of borazine with

acetylene in presence of Wilkinson’s catalyst [RhH(CO)PPh3]. Pyrolytic

decomposition of poly(vinylborazine) in ammonia at 1200-1400°C produced white

crystalline h-BN. Preparation of poly(styrene-co-β-vinylborazine) by reacting

β-vinylborazine with styrene in presence of AIBN has also been reported.201

Perdigonmelon et al.202 prepared BN catalyst supports from molecular

precursors and demonstrated the influence of the precursor on the properties of

BN ceramic. Fine powders and foams of boron nitride have been prepared from

various molecular precursors for use as noble metal supports in the catalytic

conversion of methane. A molecular precursor derived from trichloroborazine

(TCB), after reaction with ammonia at room temperature and then thermolysis

up to 1800°C, gave BN. The aminoborazine-derived precursors when thermolyzed

gave BN, expanded like foam.

Toury et al.203 prepared boron nitride fibers from symmetric and

asymmetric alkylaminoborazines. The thermolysis of 2,4,6-[(CH3)2N]3B3N3H3,

2,4-[(CH3)2N]2-6-(CH3HN)B3N3H3 and 2-[(CH3)2N]-4,6-(CH3HN)2B3N3H3 led to

different types of polyborazines. Polyborazine filaments were prepared and

subjected to thermal treatment up to 1800°C to obtain h-BN fibers.

20 Chapter 1

1.2.2 Decaborane(14)-based polymers

The reaction of decaborane(14), B10H14, with Lewis bases (ligands, L) was

reported for the first time by Schaeffer in 1957.204 Following this discovery, a

number of such derivatives were prepared using various nitriles, amines,

phosphines, sulfides and other ligands. In the formation of B10H12L2 (Scheme 1. 6),

hydrogen atoms at 6 and 9 position of the B10H14 framework are displaced by

electron pair donor atoms.205

Scheme 1. 6. Formation of B10H12.L2

Incidentally, the ligand, L, in B10H12.L2 can be displaced by another ligand

having a higher bonding strength, thus offering an alternative synthetic route for

the synthesis of bis(ligand adduct)s of decaborane. It is obvious that if a bidendate

ligand is used in place of L for the synthesis of B10H12.L2, a linear polymer can be

obtained. (Scheme 1.7)

B10H14 + L~~~~~~~L [B10H12.L~~~~~~~L]n

Scheme 1.7. Synthesis of decaborane-based polymers

Following the report by Parshall206 on the synthesis of a decaborane-

based linear polymer from P,P,P',P'-tetraethylenediphosphine, various polymers

were synthesized from Lewis bases such as phosphines, nitriles and amines.

Polymeric Lewis base adducts of decaborane can be prepared in organic

solvents such as benzene, hexane, toluene, xylene, diethylether and THF.

Introduction 21

Most of these polymers are soluble in polar solvents such as dimethylacetamide

(DMAc), dimethylformamide (DMF), N-methylpyrolidone (NMP), hexamethyl-

phosphoramide (HMPA) and dimethylsulfoxide (DMSO). The solubility of these

polymers appears to depend on the nature of the bridging ligand.

In general, [B10H12.L~~~~~~~L]n polymers give high char residue

(70-90%) in inert atmosphere. The fact that these polymers lose very little weight

on pyrolysis suggests the presence of "thermolabile functionality".207 In the case of

[B10H12.L~~~~~~~L]n polymers, the acidic bridging B-H-B bonds of the B10H12.L2

cage unit may serve as "thermolabile functionality”. On thermal treatment,

B10H12.L2 cage may be converted into (LH+)2 B10H102-.

Seyferth and Rees207 reported that decaborane-based polymers undergo

degradation in DMAc. Packirisamy et al.208, 209 studied the effect of various polar

solvents on the stability of these polymers using 11B-NMR spectroscopy. 11B-NMR

spectra of the decaborane-based polymers were recorded in DMF and DMSO.

It was found that the polymer has undergone degradation in these solvents

resulting in the formation of more than one degradation products. One of the main

degradation products is B10H102-. Studies revealed that there is no salt formation

during the synthesis, but on standing the complex incorporates oxygen resulting in

the formation of small amount of the salt. Polar solvents favor proton transfer from

B10H12 cage of a B10H12L2 complex to the ligand and in a less polar solvent such a

proton transfer is less favored. The proton transfer mechanism which is operative

in polar solvents is shown below:

B10H12.L2 ↔ B10H12.L + L

B10H12.L + Base → B10H11- + [Base.H]+ + L

B10H11- + Base → B10H102- + [Base.H]+

Packirisamy et al.9,208,209 synthesized B and Si containing polymer which is

the first decaborane polymer reported soluble in THF (less polar solvent compared

to DMAc, DMF and DMSO) through the reaction of decaborane with

1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane and evaluated it as an atomic

oxygen (AO) resistant coating for low earth orbit space structures.

22 Chapter 1

Decaborane-based polymers serve as precursors for boron nitride and

boron carbide ceramic materials9,210-213 and as atomic oxygen resistant

coatings.9,208,209 Ambadas122 synthesized B and Si containing polymers through

the reaction of decaborane with different types of aminosiloxanes, namely,

3-aminopropyl- triethoxysilane (APTEOS), 3-aminopropylmethyldiethoxysilane

(APMDEOS) and aminopropyl terminated polydimethylsiloxane (APPDMSiO).

New decaborane-based, single-source molecular and polymeric

precursors to B4C were developed by Sneddon et al.214 that enable the formation

of boron carbide in processed forms, including nanofibers, nanocylinders and

nanoporous materials. Sneddon et al.215,216 reported the synthesis,

characterization and ceramic conversion of a polyborosilazane that can be

prepared via the reaction of commercially available polysilazane, namely

CERASET®, with decaborane. Depending on the pyrolysis conditions, these new

polymers can serve as excellent precursors to SiC/BN ceramic compositions.

Forsthoefel and Sneddon217 obtained metal boride precursors by

dispersing metal oxides in decaborane-dicyanopentane polymer. Pyrolysis of the

metaloxide/polymer dispersions gave metal borides, including TiB2, ZrB2 and HfB2

in high yield. Metal-boride/nitride composites including TiB2/TiN and HfB2/HfN

materials were also readily obtained by pyrolysis of metal dispersions in

polyborazylene, (B3N3H4)x. The high ceramic yield of metal boride/nitride systems

(~ 98%) enables their use for the controlled formation of shaped monolithic

TiB2/TiN or HfB2/HfN materials on pyrolysis. Better results were obtained when

polyhexenyldecaborane polymer was used. Boron-containing ceramics, in

particular, ceramic fibers were obtained by heat treatment of precursor fibers

drawn from decaborane-amine and decaborane-phosphine polymers in inert

atmosphere.218-221

1.2.3 Polymers derived from vinylpentaborane

2-(Vinylpentaborane) when heated at 125°C gets converted to

poly(vinylpentaborane).222,223 A crosslinked polymer was obtained when

poly(vinylpentaborane) was heated to 140°C, where B-B linkages were formed by

Introduction 23

the loss of hydrogen and the crosslinked polymer on pyrolysis in argon at 1200°C

gave B4C in 77% yield.

1.2.4 Polymers derived from boric acid

Wada et al.224 reported the conversion of borate esters synthesized from

boric acid and 1,2,3-propanetriol to ceramics in 1985, though the synthesis and

properties of this polymer was reported as early as 1964.225 A glassy, colorless

transparent product was formed which showed spinnability on heating. Pyrolysis of

this polymer at 1200°C yielded B2O3 regardless of the gas used and duration of

heating. When the polymer was heated above 1300 °C in nitrogen, BN and B4C

were formed, whereas B4C was formed when the polymer was heated in argon at

1400°C. The crystallinity of the ceramics increased with increase in heat treatment

temperature and heating time. Wada et al.226 studied the reaction between boric

acid and diethanolamine as well as triethanolamine as a means of preparing

precursors for BN ceramics. A glassy polymer obtained on pyrolysis under

nitrogen at 1400°C gave BN and small amount of B4C.

Mondal et al.227 used the borate ester synthesized by condensation of

boric acid and triethanolamine to obtain a hard, carbon coating with boron nitride

and carbonitride on glass fiber which was used for filtration of molten aluminum.

Tian et al.228 synthesized crystalline hexagonal B(N1-xCx) and cubic B-C-N

ceramics from a precursor produced from melamine and boric acid by application

of high temperature and high pressure. A low temperature synthetic route for

boron carbide was developed by Mondal and Banthia.229 A polymeric precursor

was synthesized by the reaction of boric acid and polyvinylalcohol which on

pyrolysis at 400°C and 800°C gave B4C. X-ray diffraction shows that B4C obtained

by this method has orthorhombic crystal structure.

1.3 Boron and silicon containing polymers

Synthesis of boron and silicon containing polymers has gained importance

due to their superior thermo-chemical properties.230,231 These polymers on

pyrolysis at higher temperatures give non-oxide ceramics such as silicon boride,

24 Chapter 1

SiC-B4C and borosilicon carbonitride. Ceramics derived from boron and silicon

containing precursors are found to remain amorphous even up to 2000°C.232

Boron and silicon containing ceramic, when exposed to oxidizing

environment at high temperature, forms a protective borosilicate glassy layer on

the surface, which prevents further oxidation of the ceramic. Boron and silicon

containing polymers are mainly prepared by the following four synthetic methods:

(i) by reacting functional monomers of boron with functional monomers of silicon,

(ii) by reacting functional monomers containing both boron and silicon with

functional monomers of silicon, (iii) by chemical modification of organosilicon

polymers with boron compounds and (iv) through the reaction of single source

precursor containing both boron and silicon with suitable comonomers.

1.3.1 From functional monomers of boron with functional monomers of

silicon

Borosiloxane oligomers/polymers synthesized from boric acid/borate

esters with functional monomers of silicon fall under this category. As the present

thesis deals with borosiloxane oligomers, the literature on this topic is dealt with in

a separate section.

Synthesis of boron and silicon containing polymers reported by Ricitiello

et al.233-235 involves the dehalogenation of borontrichloride and

dialkyldichlorosilane such as DMDCS or MVDCS in presence or absence of

methyliodide in hydrocarbon solvents. Gutenberger et al.236 synthesized

poly(borodiphenylcarbosilane) free of oxygen by reacting DPDCS,

dibromomethane and phenyldichloroborane or borontribromide with sodium.

Sundar and Keller237 synthesized acetylinic polymers by reacting

1,4-dilithiobutadiyne with phenylboron dichloride and DMDCS. The incorporation

of silicon and boron into the diacetylinic polymer was found to enhance the

oxidation stability of the polymer. They also reported238 the synthesis of

borocarbosilicate polymer containing diacetylinic functionalities with improved

thermal properties, by reacting DPDCS and 1,4-dilithiobutadiyne with

Introduction 25

phenylboronic acid. Boron and silicon containing polymers having acetylinic units

in the backbone were also synthesized by reacting bis(dimethylchlorosilyl) -

benzene with phenylboronic acid.239

1.3.2 From functional monomers of boron and silicon with functional monomers of silicon

Poly(carborane-siloxanes)s synthesized from functional monomers of

boron and silicon with functional monomers of silicon represent another class of

boron and silicon containing polymers. Poly(carborane-siloxane)s marketed under

the trade name "Dexsil" contain carborane units along with siloxane units in the

backbone (Structure 8). Dexsil polymers are prepared by the condensation

polymerization of bis(methoxydimethylsilyl)-m-carborane with alkylchlorosilane or

alkylchlorosiloxane or bis(chlorosilyl)-m-carborane derivatives in presence of a

catalyst240-245

Structure 8. Structures of different poly(carborane-siloxane)s

Dexsil 202 is a viscous liquid and consists of m-carborane cage attached

to a dialkyl or diarylsiloxane unit with a small amount of 1-vinyl-o-carbonyl side

group to enhance the crosslinking. Dexsil polymer serves as a precursor for boron

and silicon containing ceramics.246,247 The incorporation of carborane units

prevents the degradation of polysiloxanes by ring forming depolymerization and

n Dexsil 100 crystalline polymer

CH 3

Si B 10 H 10 C C Si O

CH 3

CH 3

CH 3

n Dexsil 200 elastomer

Si B 10 H 10 C C Si O Si O

CH 3

CH 3

CH 3

CH 3

CH 3

CH 3

n

Dexsil 300 elastomer

Si B 10 H 10 C C Si O Si O

CH 3

CH 3

CH 3

CH 3

CH 3

CH 3

Si

CH 3

CH 3

26 Chapter 1

enhances the resistivity towards high temperature degradation particularly in inert

atmosphere. Pyrolysis of these polymers in nitrogen atmosphere led to the

degradation of carborane cage at around 700°C leaving an amorphous

borosiliconoxycarbide (BSiOC), which got converted to β-SiC and B4C on further

heating to 1300°C by the carbothermal reduction of BSiOC phase.

A highly functionalized carborane-siloxane polymer was synthesized by

Kulig et al.248 from l,7-bis(hydroxydimethylsilyl)-m-carborane and methyltriacetoxy-

silane. The polymer formed has one acetoxy crosslinking site per repeat unit. This

polymer has a molecular weight of 6,000 and is soluble in THF and toluene. This

polymer was evaluated as an AO resistant coating for low earth orbit space

structures.248,249

1.3.3 Chemical modification of organosilicon polymers

Niebylski250,251 synthesized organoborosilazane polymers by reacting

trialkoxy, triaryloxy or tri(arylalkoxy)boroxine with polysilazane. Chemical

modification of hydridopolysilazane was performed by reacting it wi th liquid

borazine at low temperatures to obtain boron and silicon containing

polymers.252,253 Chemical modification of hydridopolysilazanes with

monofunctional boranes such as pinacolborane (Me2CO)2BH, l,3-dimethyl-l,3-

diaza-2-borocyclopentane (CH2NMe)2BH and 2,4-diethylborazine (Et2B3N3H4) has

also been reported.254

Chemical modification of silazanes with borane-dimethylsulfide was

studied by Seyferth et al.255 In this method oligomeric silazane (CH3SiHNH)n was

treated with BH3.S(CH3)2 to obtain a crosslinked polyborosilazane. The polymer

obtained as a low melting white solid has molecular weight of 800.

Polyborosilazane was also derived from perhydropolysilazane and

trimethylborate.256 Polyborosilazane with low oxygen content was synthesized by

reacting perhydrosilazane with tris(dimethylamino)borane.257

The synthesis and thermal behavior of boron-modified polysilazanes

{B[C2H4Si(R)NH]3}n and polysilylcarbodiimides {B[C2H4Si(R)NCN]3}n were reported

by Aldinger and Weinmann (Scheme 1. 8).258

Introduction 27

Si

BCHR

R'CH3

ClX

CH2H

NH3

R=H,CH3,ClR'=C2H4Si(R)Cl2

X=NH,N=C=NR=H,CH3,X0.6 R=H,CH3

R'=C2H4Si(R)H2

Me3SiN=C=NSiMe3

X=NH,N=C=NR'=C2H4SI(R)X

Si-B-C-N

Cl

R

Si

Si

Si

C

R

R

R

BR'

R' CHCH3

H H

or BH3-SMe2 NH3,[nBuLi]

CH

CH3BR'

R'

R=H,CH3,X0.6

Ceramization

ceramic

n

12

3

nX

Scheme 1. 8. Synthesis of boron-modified silazanes

These Si-B-C-N ceramic precursors were obtained by treating vinyl

substituted polysilylcarbodiimides [(H2C=CH)(R)-SiNCN]n with borane-dimethyl-

sulfide BH3.S(CH3)2. The polysilylcarbodiimides themselves were synthesized via

treatment of vinyl-substituted chlorosilanes (H2C=CH)(R)SiCl2 with cyanamide,

H2N-C≡N, in the presence of pyridine, or via the reaction of the vinyl-substituted

chlorosilanes with bis(trimethylsilyl)carbodiimide, (H3C)3SiN=C=N-Si(CH3)3.

Alternatively, these compounds were synthesized via hydroboration of vinyl-

substituted chlorosilanes with borane-dimethylsulphide, borane-trimethyl-amide or

borane-triethylanhydride yielding tris[(chlorosilyl)ethyl]boranes initially.

The synthesis by a novel reaction pathway and the polymer-to-ceramic

conversion of boron-containing polysilylcarbodiimides were reported by

Weinmann et al.155,259 Polysilylcarbodiimides were prepared by reaction of

tris(hydridosilylethyl)boranes with different amounts of cyanamide in THF.

28 Chapter 1

Thermolysis of such compounds in an argon atmosphere delivers Si-B-C-N

ceramics in 65-85% yield.

Polysilazanes with polymerizable pendant groups were synthesized by

Weinmann et al.260 These pendant groups enable crosslinking thereby minimizing

depolymerization during ceramization.

A new kind of polyborosilazane was synthesized by Zeng et al.261 from

hexamethylcyclotrisilazane by exposure to borontrichloride. It was observed that

the boron content of the precursor increased as the exposure time was increased

whereas the C/Si ratio remained constant. The pyrolysis of the precursor was

carried out at 1250°C, 1600°C and 1800°C in nitrogen. Heat treatment of the

polymer at 1800°C resulted in BN crystals.

Schiavon et al.262,263 synthesized poly(borosilazanes) with Si/B molar

ratios of 3 and 9, via hydroboration, of vinyl-substituted cyclotrisilazane,

[CH2=CH(CH3)SiNH]3, with borane-trimethylamine adduct, BH3.N(CH3)3.

The polyborosilazanes were pyrolyzed up to 1000°C under argon atmosphere,

which resulted in amorphous silicon boron carbonitride (SiBCN) glasses. The

SiBCN glass with B/Si= 3 was amorphous up to 1700°C and at this temperature,

β-SiC and β-Si3N4 were formed. At 2000°C, β-SiC and BN were formed. These

ceramics have a number of advantages when compared to the corresponding

B-free Si-C-N system, which include higher thermal stability, oxidation resistance,

crystallization temperature and ceramic yield.

1.3.4 From single source precursors

Baldus et al.264,265 synthesized polyborosilazane by reacting a single

source precursor, viz., chlorosilylaminodichloroborane [Cl3Si-NH-BCl2] with

methylamine to obtain a processable polymer in 80% yield. The polyborosilazane

consists of [Si3NCH3]3 six membered ring connected via. HN-B- and -N(CH3)-B-

units respectively. This polymer has an average molecular weight of 2,500 and

melts at 140°C. Prolonged heating at temperatures above 180°C caused further

crosslinking and the polymer became infusible. Pyrolysis of this polymer in argon

or nitrogen at 1650°C led to the formation of amorphous borosiliconcarbonitride

Introduction 29

[Si-B-N-C] ceramic in 70% yield and the ceramic obtained did not crystallize on

heating in nitrogen up to 1900°C. This polymer was also used for coating and for

infiltration of woven carbon fibers, carbon fiber composites and porous ceramic

materials.265

Riedel266 explored the hydroboration of MVDCS with borane-

dimethylsulfide [(CH3)2S.BH3]. Addition of (CH3)2S.BH3 to MVDCS in toluene

resulted in the formation of a precursor tris(dichloromethylsilylethyl)borane. This

organosilylboron was subsequently polycondensed with ammonia at 0°C in

tetrahydrodfuran to obtain a polyorganoborosilazane in 80% yield. Pyrolysis of this

polymer in argon at 1000°C resulted in the formation of SiBCN ceramic in 62%

yield. The crystallization of this ceramic commenced at 1700°C and the

crystallization was completed above 2000°C.

The requirement of high pyrolysis temperature for carbothermal reduction

of silicon oxide components has led to the development of oxygen free carborane-

silicon compounds. Zheng et al.247 synthesized several oxygen free boron and

silicon containing monomers. These molecules were volatile compounds due to

their low molecular weight.

The high temperature properties of poly(carborane-siloxane)s were

improved by incorporating acetylinic units in the polymer backbone. Henderson

and Keller267,268 synthesized poly(carborane-siloxane-acetylene) polymers by

reacting equal amount of 1,4-dilithiobutadiyne and 1,7-bis(chlorotetramethyl-

disiloxane)-m-carborane. A linear polymer soluble in common organic solvents

and having molecular weight wM of 4,900 was obtained in 97% yield.

The incorporation of acetylinic units in the polymer backbone has the

added advantage that they remain dormant during ambient temperatures, but can

be used for crosslinking at higher temperatures. The linear poly(carborane-

siloxane-acetylene) can be readily converted to a thermoset by thermal

crosslinking, where additional polymerization reaction occurs with out the

formation of volatile by-products. Pyrolysis of this polymer yielded a black solid

ceramic in 85% yield.

30 Chapter 1

Bucca and Keller269 investigated the possibility of incorporating boron

and silicon in arylacetylenic compounds. These monomers can be converted

to thermally stable thermosets, which on pyrolysis give ceramic like

materials. When these materials were exposed to oxidizing environment at

elevated temperatures protective inorganic oxides were formed on the surface.

These inorganic oxide layers act as a barrier to protect the interior from

degradation. Of late, they reported270 that boron and silicon containing acetylinic

monomer viz., l,7-bis(4-phenylethylphenyltetramethyl-disiloxy)-m-carborane can

be copolymerized with l,2,4,5-tetrakis(phenylethynyl)-benzene to obtain thermo-

sets and chars having outstanding thermooxidative properties.

Jansen and Kroschel271 synthesized an amorphous ceramic, SiBNC,

obtained from 1,1-dichloro-N-(trichlorosilyl)boraneamine and N-methyl polyboro-

silazane. The pyrolysis proceeds in three clearly divided steps, which can be

assigned to completion of the polycondensation (200-350°C), fragmentation (580-

620°C) and elimination of residual hydrogen (1000-1300°C).

1.4 Polyborosiloxanes

Polysiloxanes undergo degradation by forming cyclics by back-biting

mechanism. This problem has been overcome through the incorporation of

borosiloxane and metallosiloxane linkages. Polyborosiloxanes have been an

exploration target because of their thermodynamically stable backbone linkage,

despite their high susceptibility to hydrolysis. They cannot be used themselves as

high temperature polymers but show interesting properties and can be used as

precursors for ceramic binders, additives and coatings. They are also investigated

in sol-gel chemistry as precursor sols and/or as precursors for borosilicate

glasses. Several methods have been described for the synthesis of polymers

containing -Si-O-B-O-linkages using di- and trifunctional silicon compounds272,273

as the source of silicon, and boric acid, borontrioxide, borontrichloride, boron

tribromide and borate esters as the source of boron. The literature on

borosiloxanes is presented in this thesis under the following four categories: (i)

borosiloxanes from boric acid, (ii) borosiloxanes from borate esters, (iii) sol-gel

process and (iv) organically modified SiO2-B2O3 gels.

Introduction 31

1.4.1 Borosiloxanes from boric acid

Boric acid reacts with chlorosilane, alkoxysilane or silanol as shown below

resulting in the formation of borosiloxane linkage.274, 275

3R3SiCl + B(OH)3 (R3SiO)3B + 3HCl

3R3SiOR’ + B(OH)3 (R3SiO)3B + 3R’OH

3R3SiOH + B(OH)3 (R3SiO)3B + 3H2O

Dimethyldiethoxysilane reacts with boric acid to give viscous liquid soluble

in organic solvents. When methyltriethoxysilane is used, infusible and insoluble

solids are formed. Polyborosiloxanes obtained by the reaction of boric acid with

diethyldiethoxysilane are more stable to hydrolysis. In these cases, the side

reaction to form triethoxyborane is controlled.

Ambadas et al.276 prepared borosiloxane oligomers through the

condensation of boric acid with PTMOS and VTEOS in diglyme at 150-160°C. These oligomers give ceramic residue in the range of 68-85%. Borosiloxane

oligomer containing vinyl group gives higher ceramic residue compared to the one

containing phenyl group and this is attributed to the crosslinking of vinyl groups.

Yajima et al.273 synthesized poly(borodiphenylsiloxane) by reacting boric acid with

DPDCS in n-butylether under nitrogen atmosphere for 18 h at 300°C

(Scheme 1.9).

Scheme 1. 9. Synthesis of poly(borodiphenylsiloxane)

The above polymer was obtained in 92% yield and found to be far more

moisture resistant than its analog prepared from boric acid and DMDCS.

Poly(borodiphenylsiloxane) softens at 100°C and is stable up to 500°C when

heated in air. The use of this polymer as a catalyst for the thermal conversion of

PDMS to polycarbosilane has been discussed in the section on polysilanes.

Ph

+Cl ClSi

Ph

B(OH)3Cl Si

Ph

Ph

Ph

O B Si OO

n

n-butylether

300°C

32 Chapter 1

Kobayashi277 reported the preparation of borodiphenylsiloxanol by the

condensation reaction of boric acid and diphenylsilanediol and then

polycondensing the borodiphenylsiloxanol to obtain borosiloxanes with wM

ranging from 800-5000.

Hoshii et al.278-280 synthesized borodiphenylsiloxane oligomers by reacting

diphenylsilanediol with boric acid (in different mole ratios) at 300°C in nitrogen

atmosphere in presence of dibutylether and N-methyl-2-pyrrolidone. The

oligomers have molecular weight ( nM ) in the range of 510 to 610 and gave a

ceramic residue of 59-70% when pyrolyzed at 1000°C.

1.4.2 Polymers from borate esters

Among the borate esters tris(trialkylsiloxy)boranes, (R3SiO)3B (R= Me, Et)

and bis(tri-t-butoxysiloxy)-n-butoxyborane have been reported as model

compounds for preparation of polyborosiloxanes.274 The reaction of chlorosilanes

or silanols with trialkoxyboranes277 results in the formation of polyborosiloxanes.

Partially hydrolyzed tetraethoxysilane reacts with trialkoxyborane, followed by further hydrolytic polycondensation to give borosilicate via sols and borosiloxane gels.281

Since polyborosiloxanes formed in a sol-gel process are unstable and

could not be isolated, heterofunctional polycondensation of tetraacetoxysilane and

tri-n-butoxyborane has been investigated to prepare and characterize the

polymers.281 The reaction provides only a low molecular weight polymer

( nM = 300-400). However, polyborosiloxanes of nM more than 5000 (HPBS),

which show good spinnability, were obtained by controlled alkoxylation, followed

by partial hydrolysis and final condensation in a sealed flask (Scheme 1.10). Dry

spinning of polymers (HPBS) provides SiO2-B2O3 precursor fibers.282

Scheme 1. 10. Preparation of polyborosiloxanes and/or SiO2-B2O3 gels

Si(OAc) 4 B(OBu n ) 3

THF Reflux BS

TAS TBB

Alkoxylation with EtOH Partial hydrolysis PBS

PBS HPBS Condensation/60 C

+

Introduction 33

Polyborosiloxanes and gel fibers were more easily prepared by reacting silicic acid and tributylborate in various molar ratios as shown in Scheme 1.11. The solution was concentrated in vacuum and then allowed to stand in a sealed flask at room temperature or at 60°C for a certain time to form a viscous solution from which gel fibers could be drawn just before gelation.

Scheme 1.11. Preparation of polyborosiloxanes from silicic acid Beckett et al.283 reported the synthesis of alkali-free borosilicate gel from

Si(OEt)4 and (MeO)3B3O3 in non-aqueous solvents. The formation of the gel proceeds via rapid transesterification/oxygen transfer with elimination of B(OR)3 followed by removal of volatiles from the gel and then drying at 60°C and subsequent heating in air at 600°C resulted in alkali-free borosilicate glass.

Synthesis of borosiloxanes through the reaction of borontrialkoxide with dialkyldiacetoxysilane or tetraacetoxysilane was reported by Kasgoz et al.284,285

These polymers were investigated as precursors for preparation of homogeneous borosiloxane gels.

Pillot et al.286 prepared polyborosiloxanes by the condensation of polychlorosilane and an alkylborate, B(OR)3, in presence of a catalyst. This polymer on nitridation followed by pyrolysis gave crystalline boron and silicon oxynitride ceramics.

1.4.3 Sol-gel process

It involves the preparative techniques heavily based on chemical reactions, for example, the generation of ceramic type materials by the hydrolysis of an organometallic compound. The sol-gel name applied to this approach comes

HO Si O H

OH

B(OBun)3

OH n

Mn=1000

Mn=6000

nOH

HO

OH

OSi B O

OBun

Bun

x

nOH

HO

OBun

OSi B O

OBun

Bun

x

nBuOH/Conc.

34 Chapter 1

from the fact that, in at least some of these synthesis, a dispersion of particles called a sol is produced and these particles can aggregate into gels as intermediates to final ceramic like materials. The most important reaction of this type involves the catalytic hydrolysis of tetraethoxysilane (TEOS).287 Hydrolysis and condensation reactions in an anhydrous sol-gel system comprising TEOS, boric acid and ethanol were studied by Zha et al.288 Boric acid is able to hydrolyse TEOS directly, and subsequent condensation reactions form borosiloxane and siloxane linkages whereas in an aqueous system, borosiloxanes are unstable to hydrolysis and are formed only upon heat treatment of the gel. The anhydrous mixture is stable indefinitely against gelation, but can be readily gelled by addition of NaOH in ethanol and this system is useful for preparing borosilicate glasses at lower temperatures with good homogeneity.

Borophosphosilicate glass–ceramics has been synthesized by Li et al.289

by sol–gel process using boric acid, phosphoric acid and TEOS as starting

precursors. The borophosphosilicate glass–ceramics can be sintered below 950°C

in air. It was found that the SiO2 glass phase wraps up BPO4 crystallites and

Si3(PO4)4 crystallites exist when the SiO2 content is decreased. The glass

ceramics show good potential as dielectric materials in super high frequency multi-

layer chip inductors (MLCI).

Different precursors were synthesized through the sol-gel process using

tetraethoxysilane, triethylborate and polydimethylsiloxane by polycondensation

between the Si(OH) groups from the hydrolyzed tetraethoxysilane and the

polydimethylsiloxane.290 Mixed vitreous oxycarbide glasses containing silicon and

boron were prepared by pyrolysis of the hybrid precursors in nitrogen at 1100°C.

The spectral studies indicate that boron is not incorporated into the network until

pyrolysis of the precursors that form the oxycarbides. The oxycarbides were

porous made of spherical interconnected particles and the porosity and mean pore

size of the glasses increased with increase in triethylborate content.

Sodium silicate solutions were mixed with boric acid in order to form

sodium borosilicate gels and the gelation process was studied by Boschel and

Roggendorf.291 The effect of composition and temperature on the gel point was

studied in detail.

Introduction 35

A patent literature292 discloses a process for the borosilicate glass

formation. Silicontetraalkoxide and borate ester were combined with water in

excess of that required for hydrolysis of alkoxide groups and the alkanol and water

formed were removed by fractional distillation from the reaction product to obtain

borosilicate glass.

1.4.4 Organically modified SiO2-B2O3 gels

Preparation of binary SiO2-B2O3 gels as precursor for borosilicate glasses

has been reported by several authors293-298 using sol-gel process. Sol-gel process

was chosen with the aim of preparing, via cocondensation reactions between

TEOS and triethylborate or boric acid, a more homogenous network compared to

the traditional melting route.

SiO2-B2O3 gels, have been extensively studied as precursors for

borosilicates or oxynitride glasses. It is found that the boron atoms are present in

the silica matrix as a separate B2O3 and/or B(OH)3 phase.296,297 This is probably

due to the well known reactivity of the B-O-Si bonds towards hydrolysis. The

borosiloxane linkages that might form in the early stages of the sol-gel process are

consumed at the end when increasing amount of water is produced via

condensation.298 Soraru et al.299 have recently shown that if a modified silicon

alkoxide, such as RSi(OEt)3, where R = Me, Et or Vi is cohydrolyzed with

tetraethylborate, then a large amount of trigonal BO3 units are incorporated in the

hybrid siloxane-network via B-O-Si bridges, leading to borosiloxane gels. The

resulting gels appear homogeneous, clear and no evidence of the formation of a

crystalline B(OH)3 can be detected. The retention of B-O-Si bonds in the hybrid

borosilicate gels is partly due to: (i) the low hydrolysis ratio used in the sol-gel

synthesis (H2O)/Si = 1.5), (ii) the in situ protection that the hydrophobic organic

groups bonded to silicon provide against water attack and (iii) the higher electron

density at the silicon atoms in the organically substituted gels which strengthen

the Si-O bonds.

In a modification of the above approach, the production of homogenous

borosilicate gels were tried by a new process in which the modified silicon

36 Chapter 1

alkoxides are directly reacted with boric acid without any external addition of

water.300 Here the hybrid borosilicate gels were synthesized according to a new

route, by adding boric acid to the liquid silicon alkoxide and by stirring until its

complete dissolution. The clear solutions were then cast in plastic test tubes that

were left open for gelation. Wet gels were dried for at least 10 days at 60°C. 11B-MAS NMR spectroscopic studies showed the formation of homogeneous

borosilicate gels and the incorporation of boron atoms into the siloxane network

via B-O-Si bridges. On the other hand, when a conventional tetrafunctional silicon

alkoxide such as TMOS or TEOS is reacted with boric acid the expected

borosilicate gels are not formed. The homogeneous borosilicate, obtained from

boric acid and alkoxysilanes, on pyrolysis results in the formation of homogeneous

amorphous borosilicon oxycarbide (BSiOC) glasses.301

The structural conversion of silicate gel to glass was investigated by Yang

and Woo302 in the temperature range of 150-850°C by using solid-state 1H- and 29Si-NMR spectroscopy. The conversion process is continuous and dependent on

the stabilization temperature. The silicate gel to glass conversion process is

completed at 850°C. The incorporation of boron in silicate backbone provides the

formation of ≡Si-O-B= bonds which results in the formation of borosilicate gels.

1.4.5 Applications of borosiloxanes

The end uses of preceramic polymers are dealt in detail in next section.

As the present thesis deals mainly with borosiloxane oligomers, specific end uses

of polyborosiloxanes are dealt in some detail in this sub section.

Polyborosiloxanes find end-uses as catalysts for the conversion of

polydimethylsilane to polycarbosilane, binders for making SiC components and

precursors for SiC-B4C ceramics and thermal protection coatings.272,276,303-315

Polyborosiloxanes synthesized by sol-gel process, are used for preparing

borosilicate bulk bodies, powders, thin films and fibers with high purity and

molecular homogeneity under mild conditions.284,316,317 Borosilicates are known to

be especially useful as cladding material for wave guides. Since they have a lower

refractive index than pure fused silica, low attenuation in glass fibers is more

Introduction 37

easily achieved.318-320 They have also been used as passivation layers for

microelectronic devices and as heat-resistant inorganic fibers.321-323

Polyborosiloxanes serve as binders, coatings and heat-resistant paints for

far infrared ray irradiators80, exhaust systems of cars and electric wires.324,325 A

metal plate can be coated to a thickness of 5 µm with a polyborosiloxane layer

containing metal oxides to form a solar collector.326

A patent literature explains a process for producing a heat-resistant

ceramic sintered body, which comprises preparing polycarbosilane containing

siloxane bonds by addition of polyborosiloxane containing phenyl groups with a

part of the side chain of Si and skeletal structure B, Si and O attached to

polysilane and heating the reaction mixture in an inert atmosphere. The

polycarbosilane obtained was mixed with a ceramic powder from the group

consisting of oxides, carbides, borides and silicides and sintering the mixture at a

temperature from 800 to 2000°C.327

Polyborosiloxane find wide variety of end-uses such as adhesive for

joining two substrates,328 curing agents for epoxy resins,329-331 and as heat curable

polymers.332

1.5 End uses of preceramic polymers

Preceramic polymers find wide range of applications as high temperature

polymers, high temperature rubbers, thermal protection systems, and oxidation

resistant coatings, matrix resins for ceramic matrix composites, precursors for

ceramic fibers, binders for making ceramic components and precursors for

obtaining ultra-fine ceramic powders. End-uses of some of the preceramic

polymers whose synthesis were dealt with in the preceding sections are discussed

in this section.

1.5.1 Protective coatings

Organometallic polymers find application as protective coatings for a

variety of substrates including carbon/carbon composites, carbon/graphite fibers,

ceramic fibers, ceramic matrix composites, metals and metal oxides.333-339

Protective coatings derived from organometallic polymers offer potential

38 Chapter 1

advantages over the conventional methods. The advantages include short

processing time, processing flexibility, ability to form coating on complex shaped

objects, processing at low temperature enabling ceramic formation under milder

conditions, high purity of the final ceramic, precise control of ceramic composition,

ability to apply multiple coating with relative ease and tailoring the coating

chemistry to obtain desired properties.336 A detailed discussion on various

preceramic polymer systems used as coatings is made in chapter 3.5.

Besides their end-uses as high temperature resistant materials,

precursors for ceramics and oxidation resistant coatings for carbon-based

substrates, inorganic and organometallic polymers find utility as atomic oxygen

(AO) resistant coatings for low earth orbit (LEO) space structures.208 A

comprehensive account of different polymeric systems used as AO resistant

coatings is given in Chapter 3.7.

1.5.2 Ceramic fibers

Preparation of ceramic fibers from organosilicon polymers was first

reported by Yajima et al.2,339,340 SiC fiber was obtained by a process which starts

from DMDCS and involves the synthesis of polysilane and its conversion to

polycarbosilane by heat treating it in an inert atmosphere under pressure around

450°C or in presence of borodiphenylsiloxane catalyst at 350°C. Green fibers (10-

20 µ m diameter) were obtained by melt spinning the precursor. They were made

infusible by surface oxidation and then subjected to pyrolysis at 1400°C to get SiC

fibers. The presence of oxygen in the final ceramic fibers is a draw back

associated with this process.

Silicon carbide fibers with low oxygen content (<2%) were prepared by

suitably modifying the spinning or curing process of green fibers followed by

pyrolysis.341 SiC fiber with low oxygen content was also obtained by pyrolyzing the

green fibers drawn from a blend of polycarbosilane and hydroxy-terminated

polybutadiene.342 Hasegawa and Okamura343 observed that the incorporation of

hetero atoms such as titanium, zirconium or vanadium into the precursor polymer

Introduction 39

enhanced the thermal stability of the ceramic fibers formed. Meyer et al.344

explored the use of silylene-acetylene polymer as a precursor for preparing SiC

fibers. Preparation of silicon oxynitride fibers by pyrolysis of polycarbosilane fibers

in ammonia345 and silicon carbonitride fibers by pyrolysis of polysilazane fibers in

inert atmosphere were reported.139,140 Silicon nitride ceramic fibers were also

prepared by heating the polymeric fibers derived from perhydropolysilazane.346

Various other preceramic polymers have been prepared and evaluated as

precursors for SiC fibers.347-353 Fibers made of SiBNC were derived from a single

source precursor, Cl3Si(NH)BCl2 and it retained the mechanical strength, as

measured by creep resistance and tensile strength, up to 1400°C.354 A variety of

borylborazine-based polymers were successfully converted into BN fibers via the

preceramic polymer route.355 Recently, Sneddon et al.214 developed new

decaborane-based polymeric precursors to B4C nanofibers.

1.5.3 Binders for ceramics

Current techniques of preparing ceramic components are based on

pressureless sintering of green body. The major drawback associated with this

process is that the voids often remain in the final structure and these voids have a

deleterious effect on the structural properties of ceramic. When preceramic

polymer is used for making green body, the void that would have formed during

organic binder burn-out would be replaced by a polymer-derived ceramic.356 The

first reported literature in this field was by Yajima et al.357 where a three

dimensional polycarbosilane was used as a binder for SiC sintered bodies.

Following this invention, Yajima et al.304 studied borodiphenylsiloxane as binders

for SiC and Si3N4 sintered bodies. Polysilastyrene358 was used as a binder for

making SiC components from β-SiC powder, and polycarbosilane and

polysilazane were used as binders for making injection moulded silicon nitride

parts.359,360 Sawai et al.152 reported that the compaction of SiC ceramic

was improved when polycarbosilane containing organofluoric groups was used

as a binder.

40 Chapter 1

1.5.4 Matrix resins for CMC

CMCs are tough materials and show a high failure stress when the fiber-

matrix bonding is either too strong or too weak. The bonding strength is usually

obtained through the use of the fiber coating referred to as the interphase. CMCs

are used as thermostructural materials under severe service conditions like high

temperatures under load and in corrosive atmospheres. The most common CMCs

used are non-oxide CMCs mainly C-SiC and SiC-SiC, the fibers being specified

first. There are three constituents in a CMC, which are the reinforcement, a matrix

and generally an interphase. The nature, volume fraction and arrangement of the

constituents depend on a number of factors including the function of the part to be

fabricated, the service conditions and the cost.

Ceramics by themselves have low fracture toughness and they fail

catastrophically. Reinforcing them with fibers increase their fracture toughness

thereby preventing catastrophic failure of the composite. Incorporation of fibers,

whiskers or particles into a ceramic matrix can result in a tough material. The

introduction of the reinforcement into the matrix results in energy-dissipating

phenomenon such as debonding at the fiber-matrix interface, crack deflection,

fiber bridging and fiber pullout.361 In this regard, proper control of the interface

region characteristics assumes great importance. The ratio of the moduli of the

reinforcement to that of the matrix is generally between 10-100 for a polymer or

metal matrix composite, while for CMC it can frequently be equal to or lower than

unity. The high ratio in polymer or metal matrix composites allows an efficient load

transfer from the matrix to the fibers through the strong interface. In a CMC, the

low modulus ratio infers that the fibers and the matrix are not much different in

their load bearing capacity. Thus, the role of the fiber reinforcement is to enhance

the toughness and strength of the composite by bridging the matrix cracks. This

requires a relatively weak interphase between the matrix and the fibers, so that

the matrix cracks induce interfacial debonding rather than failure of the fiber as the

cracks traverse the specimen’s cross-section. Accordingly, the interphase has a

key role in CMC eventhough its volume fraction is extremely low. This thin coating

which is deposited on fibers or formed in situ during composite processing serves

the functions of load transfer, crack deflection and diffusion barrier in reactive fiber

Introduction 41

matrix systems. The best interphase materials are pyrocarbon (PyC), hexagonal

BN or a layered microstructure like (SiC-PyC)m. The interphase coatings are

usually obtained by CVD process using suitable gases.361 Of late, preceramic

polymers are also used for getting interphase coatings.362 CMCs can be

processed either by conventional powder processing techniques used for

processing polycrystalline ceramics such as cold pressing and sintering, hot

pressing and reaction bonding or by newer techniques such as infiltration,

chemical vapor infiltration (CVI), sol-gel process and polymer impregnation and

pyrolysis.

Among these methods the most widely used one is the polymer infiltration

and pyrolysis. Because of the generally high cost of processing CMCs, polymer

infiltration is an attractive processing route due to its relatively low cost.

This approach allows near-net-shape molding and fabrication technology that is

able to produce nearly fully dense composites.363-367 Here, the fibers are infiltrated

with an organic polymer, which is heated to fairly high temperatures and pyrolyzed

to form a ceramic matrix. Due to the relatively low yield of polymer to ceramic,

multiple infiltrations are used to densify the composite. Polymeric precursors for

ceramic matrices allow one to use conventional polymer composite fabrication

technology that is readily available and to take advantage of processes used to

make polymer-matrix composites.364,365 By processing and pyrolyzing at lower

temperatures (compared to sintering and hot pressing) one can avoid fiber

degradation and the formation of unwanted reaction products at the fiber/matrix

interface. A detailed discussion on this topic is made in chapter 3.5.

1.5.5 Ceramic foam

There is considerable interest shown on ceramic foams which possess a

number of favorable properties such as low density, low thermal conductivity,

thermal stability, high specific strength and high resistance to chemical attack and

are suitable for industrial applications such as high temperature thermal insulation,

hot gas particulate filters, hot metal filters, catalyst supports and cores in high

temperature structural panels.368-371 The following processing routes have been

reported for the preparation of ceramic foams: (i) direct foaming of ceramic

slurries, sol-gel solutions372 or preceramic polymers (ii) chemical vapour deposition

42 Chapter 1

of various refractory materials on foamed carbon skeletons373 (iii) sintering of

hollow spheres374 and (iv) replication of polyurethane foam with ceramic

slurries.375 Of these methods, the first and the fourth one are mostly used for

making ceramic foams.

1.6 Objective and scope of the present investigation

The survey of pertinent literature on preceramic polymers presented

above reveals that the interest on these speciality polymers is ever growing. This

trend is attributed to their potential application as precursors for ceramic fibers,

ceramic coatings and ceramic foams, binders for ceramics and matrix resins for

ceramic matrix composites. Though a large amount of work has already been

done in the area of preceramic polymers and their applications, there still exists

enormous scope for developing cost effective synthetic approaches for the

preparation of novel precursors for ceramics, capable of giving high ceramic

residue. Thus, the present investigation envisages to synthesize certain speciality

oligomers/polymers containing silicon and both silicon and boron and evaluate

them as precursors for ceramics.

Among the preceramic polymers boron and silicon containing

polymers/oligomers have gained importance as they offer certain advantages

when compared to polymers which contain only boron or silicon. The ceramics

derived from such polymers remain amorphous even at temperatures exceeding

1500°C and hence, have better mechanical properties at these temperatures

compared to simple non-oxide ceramics which undergo extensive crystallization.

While several synthetic approaches are reported for the preparation of boron and

silicon containing preceramic polymers, cost effective and simple method to

prepare these polymers is by alkoxysilanes with boric acid, a cheap source of

boron. Though considerable literature is available on the synthesis of

borosiloxanes by sol-gel process there appears to be very limited information on

the synthesis of these polymers by non-aqueous sol-gel process. Thus, the main

objective of the present investigation is to synthesize novel borosiloxane

oligomers by non-aqueous sol-gel process, evaluate them as precursors for

ceramics and study their end-uses for space applications.

Introduction 43

While designing a preceramic oligomer/polymer, one should bear in mind

that it should be processable, i.e., soluble in organic solvents and/or meltable and

should give ceramic residue in high yield. To achieve this objective, it is required

to carryout a systematic investigation on the synthesis of borosiloxanes by using

different alkoxysilanes, varying the monomer feed ratios and experimental

conditions. To begin with attention has been focused on synthesizing borosiloxane

oligomers by reacting boric acid with phenyltrimethoxysilane (PTMOS) and

phenyltriethoxysilane (PTEOS). As PTEOS is much cheaper than PTMOS

emphasis has been laid on synthesizing borosiloxane oligomers from the former.

Synthesis of borosiloxane oligomer from boric acid and

vinyltriethoxysilane (VTEOS) has been reported by Ambadas.122 The choice of

VTEOS is justified from the fact that vinyl group present in the oligomer would

undergo crosslinking and hence would give high ceramic residue. The oligomer

synthesized from VTEOS is reported to give a ceramic residue of ~85% at 900°C

in inert atmosphere. However, a detailed study on the effect of monomer feed ratio

on the thermal stability and ceramic residue has not been reported. Thus, in the

present investigation attention has been focused on this aspect. As the presence

of vinylsiloxy units is expected to improve the ceramic residue, it would be of

interest to study the feasibility of synthesizing borosiloxane oligomers using a

mixture of VTEOS with other alkoxysilanes. The advantage of this approach is that

processable borosiloxane oligomers with improved ceramic residue can be

obtained. A detailed study has therefore been undertaken to synthesize

borosiloxane oligomers using mixtures of VTEOS with PTEOS and PTMOS.

Epoxy resins have gained significance due to their versatility and they find

extensive application as adhesives, matrix resins, potting compounds and coating.

Considerable amount of work has been done on epoxy-functionalized siloxane

resins. However, there is very little information on borosiloxanes containing epoxy

functional group. The advantage of such a resin is that unlike vinyl-functionalized

borosiloxanes which require high temperatures (above 150°C) for curing, epoxy

functionalized borosiloxanes can be cured at room temperature. This advantage

can be exploited for infiltrating porous ceramic matrix composites (CMCs) and

then curing the infiltrated resin thereby preventing the resin ooze-out from the

44 Chapter 1

composite. Keeping in view of this, in the present work efforts have been directed

towards preparing epoxy-functionalized borosiloxane oligomers by reacting boric

acid with glycidyloxypropyltrimethoxysilane (GPTMOS). As GPTMOS contains

aliphatic linkages, it is expected that the overall thermal stability and ceramic

residue of such oligomers would be lower than the ones synthesized from other

alkoxysilanes. This disadvantage could probably be overcome by incorporating

vinylsiloxy units in addition to the epoxy functional group. In view of this,

borosiloxane oligomers have been synthesized using different mole ratios of boric

acid, VTEOS and GPTMOS and characterized.

Besides other end-uses borosiloxanes are also useful as precursors for

glass coating. Such glass coatings are expected to find application as overlay

coating to seal the cracks in SiC coating applied to C-C composite. For this

purpose it is desirable to synthesize borosiloxane oligomers devoid of carbon. If

this is difficult to achieve, then the oligomers are to be designed in such a way that

the organic groups should be knocked off completely during pyrolysis much before

the formation of glass. To achieve this objective borosiloxane oligomer has to be

synthesized by reacting boric acid with alkoxysilane having no organic

substituents. One such monomer is tetraethoxysilane (TEOS). When boric acid is

reacted with TEOS, ethanol would be formed as a by-product and hence the

product obtained should contain only B, Si and O. If some unreacted ethoxy group

is present it is likely to be knocked off well before 1000°C. In the present

investigation, attempts have been made to synthesize borosiloxane oligomers by

reacting boric acid with TEOS.

For the synthesis of borosiloxane oligomers, diglyme or 1,4-dioxane has

been used as solvent. As they are high boiling solvents, it becomes difficult to

remove them and quite often the oligomers undergo gelation while attempting to

remove the solvents. Thus, it would be advantageous to synthesize borosiloxane

oligomers, particularly the functionalized ones, by solventless process. In this

approach, boric acid and alkoxysilane would be reacted directly without using any

solvent. The by-product, alkyl alcohol, formed by the reaction of B-OH and -OR

would serve as solvent for the reaction. The advantage of the solventless process

is that the viscosity and the molecular weight of the product obtained can be

Introduction 45

controlled by controlling the amount of alkyl alcohol distilled out from the reaction

mixture. Yet another advantage is that the resin synthesized can be directly used

for infiltration without any further processing. As alkyl alcohol is low boiling, it can

be removed easily. In view of these advantages, attempts have been made to

synthesize borosiloxane oligomers, particularly vinyl- and epoxy-functionalized

ones, by reacting boric acid with alkoxysilanes without using any solvent.

As discussed earlier, borosiloxane oligomers are expected to have better

thermooxidative stability compared to other preceramic polymers. Prior to finding

out suitable end-uses of borosiloxane oligomers, it is imperative to study their

ceramic conversion. In the present study, selective systems have been subjected

to pyrolysis at 900°C followed by sintering at 1400 and 1600°C. The ceramic

conversion studies gain significance due to the fact that the presence of boron is

expected to suppress the crystallization or in other words increase the

crystallization temperature. Borosiloxane oligomers synthesized from boric acid

are expected to have 2-6% boron and so it would be interesting to find out the

effect of increasing the boron content in borosiloxane oligomers. This can be

achieved only by using caged boron compounds. For this purpose, an oligomer

containing higher boron content has been synthesized by reacting decaborane(14)

with 3-aminopropylmethyldiethoxysilane followed by reaction with boric acid. The

ceramic conversion studies of this oligomer have been carried out.

In the present investigation, the possibility of using borosiloxane oligomers

as oxidation resistant coatings for carbon-carbon (C/C) composites, precursors for

high temperature glass coating and matrix resin for carbon fiber reinforced CMC

has also been studied.

Polysilahydrocarbons belong to a new class of silicon containing polymers

in which the polymer backbone consists of Si-(C)x-Si units, where x is more than

one. In recent years, a great deal of work has been carried out in the area of

polysilahydrocarbons focusing mainly on the synthesis, microstructure and

mechanism of formation and thermal stability.111-118,120-123 However, the thermal

degradation kinetics of such polymers and their end-uses have not been studied.

46 Chapter 1

Thus, in addition to the investigation on borosiloxane oligomers, the present thesis

focuses on the thermal degradation behavior of polysilahydrocarbons and their

evaluation as atomic oxygen (AO) resistant coating for low earth orbit space

structures.

The thermal degradation kinetics of polysilahydrocarbons obtained

through the dechlorination of diorganodichlorosilanes with styrene has been

carried out using four different equations. Attempts have been made to correlate

the activation energy and pre-exponential factor with the structure of the

copolymers. Similar investigation has been carried out on the polycarbosilanes

obtained by heat treatment of polysilahydrocarbons at different temperatures.

Attempts have been made to correlate the thermal behavior of polycarbosilanes

with the structural changes that take place in polysilahydrocarbons during heat

treatment.

The atomic oxygen formed by the photodissociation of molecular oxygen

in the upper atmosphere. AO can react with most of the spacecraft materials

causing surface erosion which eventually brings down the performance of these

materials drastically. Thus, it becomes essential to develop spacecraft materials

which are resistant to AO attack or apply AO resistant coatings on the spacecraft

materials which are susceptible to AO attack. When inorganic polymers or

organometallic polymers are used as protective coatings, they form a metal oxide

layer on the surface due to the interaction of the oxidation of the polymer by AO.

This oxide layer prevents further interaction of the polymer with AO, thus offering

protection to the substrate which is otherwise susceptible to AO attack. As

polysila-hydrocarbons contain disilyl linkages, these linkages can trap oxygen

forming siloxane linkages which on further reaction with AO would result in the

formation of SiO2 layer. Keeping in view of the above advantage, in the present

work polysilahydrocarbons have been evaluated as AO resistant coatings. The

performance of these polymers has been compared with other AO resistant

materials developed in the Preceramic Polymers Laboratory of VSSC and also

with phosphazene-containing polymers.

Introduction 47

References

1. E. James Mark, R. Harry Allcock and Robert West in Inorganic Polymers, Prentice-Hall Inc., New Jersey, 1992.

2. S. Yajima, J. Hayashi and M. Omori, Chem. Lett., 4 (1975) 931.

3. R. West, J. Organomet. Chem., 300 (1986) 327.

4. R. Baney and G. Chandra in Ency. Polym. Sci. Eng., F. G. A. Stone and W. A. G. Graham (Eds.), Wiley, New York, 13, 1988, p. 312.

5. R. D. Miller and J. Michl, Chem. Rev., 89 (1989) 1359.

6. R. H. Baney, M. Itoh, A. Sakakibara and T. Suzuk, Chem. Rev., 95 (1995) 1409.

7. R. M. Laine and F. Babonneau, Chem. Mater., 5 (1993) 260.

8. M. Birot, J. Pillot and J. Dunogues, Chem. Rev., 95 (1995) 1443.

9. S. Packirisamy, Prog. Polym. Sci., 21 (1996) 707.

10. F. S. Kipping, J. Chem. Soc., 119 (1921) 830.

11. F. S. Kipping, J. Chem. Soc., 125 (1924) 2291.

12. C. A. Burkhard, J. Am. Chem. Soc., 71 (1949) 963.

13. K. S. Mazdiyasni, R. West and L. D. David, J. Am. Ceram. Soc., 61 (1978) 504.

14. R. West, L. D. David, P. I. Djurovich, K. L. Stearley, K. S. V. Srinivasan and H. Yu, J. Am. Chem. Soc., 103 (1981) 7352.

15. R. West, L. D. David, P. I. Djurovich, H. Yu and R. Sinclair, Ceram. Bull., 62 (1983) 899.

16. R. West, in Ultrastructure Processing of Ceramics, Glasses and Composites, L. L. Hench and D. R. Ulrich (Eds.), Wiley, New York, 1984, p. 235.

17. R. West, Y. H. Zhang, P. I. Djurovich and H. Stuger in Sci. Ceram. Chem. Proc., L. L. Hench and D. R. Ulrich (Eds.), Wiley, New York, 36, 1986, 337.

18. M. Fujino and H. Isaka, J. Chem. Soc., Chem. Commun., 8 (1989) 466.

19. S. Gauthier and D. J. Worsfold, Macromolecules, 22 (1989) 2213.

20. R. G. Jones, R. E Banifield, R. H. Cragg, A. C Swain and S. J. Webb, Macromolecules, 26 (1993) 4878.

21. K. Matyjazewski, D. Greszta, J. S. Hrkach and H. M. Kim, Macromolecules, 28 (1995) 59.

48 Chapter 1

22. R.G. Jones, U. Budnik, S. J. Holder and W. K. C. Wong, Macromolecules, 29 (1996) 8036.

23. C. L. Schilling Jr., Brit. Polym. J., 8 (1986) 355.

24. C. L. Schilling Jr., ONR Technical Report TR 83-3 (1983).

25. C. L. Schilling Jr. and T. C. Williams, ONR Technical Report TR 83-1 (1983).

26. R. Shankar, A. Saxena and A. S. Brar, J. Organomet. Chem., 650 (2002) 223.

27. S. Hayase, R. Horiguchi, Y. Onishi and T. Ushirogouchi, Macromolecules, 22 (1989) 2933.

28. K. D. Safa and M. Babazadeh, Eur. Polym. J., 40 (2004) 1659.

29. C. L. Schilling Jr., J. P. Wesson and T. C. Williams, Am. Ceram. Soc. Bull., 62 (1983) 912.

30. D. Seyferth, T. G. Wood, H. J. Tracy and J. L. Robisoe, J. Am. Ceram. Soc., 74 (1991) 1300.

31. Z. Zhang, F. Babonneau, R. M. Laine, Y. Mu, J. F. Harrod and J. A. Rahn, J. Am. Ceram. Soc., 74 (1991) 670.

32. T. Kobayashi, T. Sakakura, T. Hayashi, M. Yumura and M. Tanaka, Chem. Lett., 21 (1992) 1157.

33. F. I. Hurwitz, T. A. Kacik, X. Bu, J. Masnovi, P. J. Heimann and K. Beyene, J. Mater. Sci., 30 (1995) 3130.

34. Y. Mu, R. M. Laine and J. F. Harrod, Appl. Organomet. Chem., 8 (1994) 95.

35. B. Boury, N. Bryson and G. Soula, Chem. Mater., 10 (1998) 297.

36. B. Boury, N. Bryson and G. Soula, Appl. Organomet. Chem., 13 (1999) 419.

37. P. Czubarow, T. Sugimoto and D. Seyferth, Macromolecules, 31 (1998) 229.

38. M. F. Gozzi, M. D. C. Calves and I. V. P. Yoshida, J. Mater. Sci., 34 (1999) 155.

39. Z. Zhang, C. S. Scotto and R. M. Laine, Ceram. Eng. Sci. Proc., in Ceramic Fibers and Coatings: Advanced Materials for the 21st century, Committee on Advanced Fibers for High Temperature Ceramic Composites, 15 (1994) 152.

40. M. Scarlet, I. S. Butler and J. F. Harrod, Chem. Mater., 6 (1995) 1214.

41. T. Iseki, M. Narisawa, K. Okamura, K. Oka and T. Dohmaru, J. Mater. Sci. Lett., 18 (1999) 185.

42. K. W. Chew, A. Sellinger and R. M. Laine, J. Am. Ceram. Soc., 82 (1999) 857.

Introduction 49

43. Z. Zhang, C. S. Scotto and R. M. Laine, J. Mater. Chem., 8 (1998) 2715.

44. P. Czubarow and D. Seyferth, J. Mater. Sci., 32 (1997) 2121.

45. M. F. Gozzi and I. V. P. Yoshida, Macromolecules, 28 (1995) 7232.

46. F. C. Schilling, T. W. Weidman and A. M. Joshi, J. Am. Chem. Soc., 113 (1991) 6711.

47. G. D. Soraru, F. Babonneau and J. D. Mackenzie, J. Mater. Sci., 25 (1990) 3886.

48. R. J. P. Corriu, D. Leclercq, P. H. Mutin, J. Planeix and A. Vioux, Organometallics, 12 (1993) 454.

49. H. J. Wu and L. V. Interrante, Polym. Prep., 32 (1991) 588.

50. Q. Liu, H. J. Wo, R. Lewis, G. E. Maciel and L. V. Interrante. Chem. Mater., 11 (1999) 2038.

51. A. T. Hemida, M. Birot, J. P. Pillot, J. Dunogues and P. Pailler, J. Mater. Sci., 32 (1997) 3457.

52. T. Iseki, M. Narisawa, Y. Katase, K. Oka, T. Dohmaru, and K. Okamura, Chem. Mater., 13 (2001) 4163.

53. H. Sakurai, A. Hosomi and M. Kumada, J. Chem. Soc. Chem. Commun., 8 (1968) 930.

54. K. J. Gon, M. D. Soo and D. P. Kim, J. Mater. Sci. Lett., 19 (2000) 303.

55. M. Narisawa, K. Okamura, T. Iseki, K. Oka, and T. Dohmaru, Advanced SiC/SiC ceramic composites: Developments and Applications in Energy Systems, Ceramic Transactions, 144 (2002) 141.

56. M. Narisawa, T. Yoshida, T. Iseki, Y. Katase, K. Okamura, K. Oka and T. Dohmaru, Chem. Mater., 12 (2000) 2686.

57. E. Hengge and G. Litscher, Angew Chem., 88 (1976) 414.

58. E. Hengge and G. Litscher, Montash Chem., 109 (1978) 1217.

59. E. Hengge and W. Kalchauer, Montash Chem., 121 (1990) 793.

60. M. Ishifune, S. Kashimura and Y. Kogai, J. Organomet. Chem., 611 (2000) 26.

61. S. Kashimura, M. Ishifune, H. Bu, M. Takebayashi and S. Kitajima, Tetrahedron Lett., 38 (1997) 4607.

62. M. Elangovan, A. Muthukumaran, M. Anbukulandainathan, Eur. Poly. J., 41 (2005) 2450.

63. H. K. Kim and K. Matyjazewski, Polym. Prep., 29 (1988) 168.

64. H. K. Kim and K. Matyjazewski, J. Am. Chem. Soc., 110 (1988) 3321.

50 Chapter 1

65. P. Boudjouk, B. H. Han and K. R. Anderson, J. Am. Chem. Soc., 104 (1982) 4992.

66. Z. J. Peng, W. J. Si, S. W. Lin, H. Z. Miao, H. J. Fu, M. N. Xie, H. Ma, H. M. Zeng and Z. S. Su, Eur. Polym. J., 38 (2002) 1635.

67. O. V. Mukbaniani, T. N. Tatrishvili and M. G. Karchkhadze, J. Appl. Polym. Sci., 85 (2002) 1047.

68. D. Vyprachticky and V. Cimrova, Macromolecules, 35 (2002) 3463.

69. O. Minge, N. W. Mitzel and H. Schmidbaur, Organometallics, 21 (2002) 680.

70. J. Chojnowski, M. Cypryk and J. Kurjata, Prog. Polym. Sci., 28 (2003) 691.

71. Y. Hatanaka, J. Organomet. Chem., 685 (2003) 207.

72. A. Watanabe, J. Organomet. Chem., 685 (2003) 122.

73. M. S. Cho, B. H. Kim, J. I. Kong, A. Y. Sung and H. G. Woo, J. Organomet. Chem., 685 (2003) 99.

74. D. Bratton, S. J. Holder, R. G. Jones and W. K. C. Wong, J. Organomet. Chem., 685 (2003) 60.

75. X. M. Liu, T. Lin, J. Huang, X. T. Hao, K. S. Ong and C. He, Macromolecules, 38 (2005) 4157.

76. T. Iwamoto, Bull. Chem. Soc. Jpn., 78 (2005) 393.

77. S. J. Holder, M. Achilleos and R. G. Jones, Macromolecules, 38 (2005) 1633.

78. S. Yajima, M. Omori, J. Hayashi, K. Okamura, T. Matsuzawa and C. F. Liaw, Chem. Lett., 5 (1976) 551.

79. S. Yajima, Y. Hasegawa, J. Hayashi and M. Imura, J. Mater. Sci., 13 (1978) 2569.

80. S. Yajima, Ceram. Bull., 62 (1983) 893.

81. S. Yajima, J. Hayashi and K. Okamura, Nature, 266 (1977) 521.

82. W. Habel, C. Naver and P. Satori, Chem. Ztg., 114 (1990) 305.

83. T. L. Smith Jr., US Patent 4631179 (1986).

84. E. Bacque, J. Pillot, M. Birot and J. Dunogues, Macromolecules, 21 (1988) 30.

85. H. J. Wu and L. V. Interrante, Chem. Mater., 1 (1989) 564.

86. D. Seyferth and H. Lang, Organometallics, 10 (1991) 551.

87. J. P. Pillot, E. Bacque, J. Dunogues and P. Orly, Ger. Patent 3717450 (1987).

88. B. Van Aefferdan, W. Habel and P. Satori, Chem. Ztg., 115 (1991) 1336.

Introduction 51

89. C. K. Whitmarsh and L. V. Interrante, Organometallics, 10 (1991) 1336.

90. W. Habel, B. Harnek, C. Nover and P. Sartori, J. Organomet. Chem., 464 (1994) 13.

91. W. Habel, L. Mayer and P. Sartori, J. Organomet. Chem., 474 (1994) 63.

92. C. L. Schilling Jr., J. P. Wesson and T. C. Williams, Org. Coat. Appl. Polym. Sci. Proc., 46 (1981) 137.

93. C. L. Schilling Jr., J. P. Wesson and T. C. Williams, J. Polym. Sci., Polym. Symp., 70 (1983) 121.

94. W. Habel, A. Oelscchlager and P. Sartori, J. Organomet. Chem., 486 (1995) 267.

95. R. Corriu, C. Guerch, B. Henner, A. Jean, F. Garner and A. Yassar, Chem. Mater., 2 (1990) 351.

96. I. S. Maghsoodi and T. Barton, Macromolecules, 23 (1990) 4485.

97. W. Habel, A. Oelschlager and P. Sartori, J. Organomet. Chem., 494 (1995) 157.

98. W. Uhlig, Prog. Polym. Sci., 27 (2002) 2255.

99. T. Ogawa, S. D. Lee and M. Murakami, J. Polym. Sci., Polym. Chem. Ed., 40 (2002) 416.

100. W. Uhlig, Polym. Adv. Tech., 10 (1999) 513.

101. L. V. Interrante, I. Rushkin and Q. Shen, Appl. Organomet. Chem.,12 (1998) 695.

102. W. Uhlig, Polym. Adv. Tech., 12 (2001) 607.

103. G. Kwak and T. Masuda, Kobunshi Ronbunshu, 59 (2002) 332.

104. P. Amoros, D. Beltran, C. Guillem and J. Latorre, Chem. Mater., 14 (2002) 1585.

105. M. Tsumura and T. Iwahara, Polymer, 31 (1999) 452.

106. S. Okuzaki, Y. Iwamoto and H. K. Koichi, J. Mater. Res., 14 (1999) 1353.

107. S. Okuzaki, Y. Iwamoto, S. Kondoh, H. K. Koichi and I. Shin, J. Mater. Res., 14 (1999) 189.

108. F. Cao, X. D. Li, J. H. Ryu and D. P. Kim, J. Mater. Chem., 13 (2003) 1914.

109. L. Interrante and N. Lu, US Patent 6809041 (2004).

110. L. V. Interrante, K. Moraes, Q. Liu, N. Lu, A. Puerta and L. G. Sneddon, Pure & Appl. Chem., 74 (2002) 2111.

111. C. L. Schilling Jr. and T. C. Williams, ONR Technical Report TR 83-2 (1983).

52 Chapter 1

112. V. B. Van Aefferden, W. Habel and P. Sartori, Chem. Ker. Zeitung, 14 (1990) 259.

113. S. Packirisamy in Polyimides and Other High Temperature Polymers, M. J. M. Abadie and B. Silion (Eds.), Elsevier Science Publishers, Amsterdam, 1991, p. 255.

114. M. Rama Rao, S. Packirisamy, P. V. Ravindran and P. K. Narendranath, Macromolecules, 25 (1992) 5165.

115. S. Packirisamy, G. Ambadas, K. N. Ninan, Inter. J. Plastics Tech., 6 (2003) 112.

116. S. Packirisamy, M. Rama Rao, P. K. Narendranath and P. V. Ravindran in Macromolecules Current Trends, S. Venkatachalam, V. C. Joseph, R. Ramaswamy and V. N. Krishnamurthy (Eds.), Allied Publishers, New Delhi, 1995, p. 92.

117. G. Ambadas, S. Packirisamy, T. S. Radhakrishnan and K. N. Ninan, J. Appl. Polym. Sci., 91 (2004) 3774.

118. S. Packirisamy, G. Ambadas, M. Rama Rao and K. N. Ninan in Macromolecules: New Frontiers, (Proc. IUPAC Int. Symp. Adv. Polym. Sci. Tech., Jan. 1998, Chennai) KSV Srinivasan (Ed.), Allied Publishers, New Delhi, 1998,p. 1003.

119. D. Devapal, G. Ambadas, S. Packirisamy, T. S. Radhakrishnan and K. N. Ninan, Thermochimica Acta, 409 (2004) 151.

120. S. Packirisamy, G. Ambadas, M. Rama Rao, V. P. Balagangadharan and K. N. Ninan, Macromolecules (to be communicated).

121. G. Ambadas, S. Packirisamy and K. N. Ninan, Macromolecules (to be communicated).

122. G. Ambadas. Ph.D Thesis, Kerala University, Thiruvananthapuram, 2000.

123. S. Packirisamy, G. Ambadas, M. Rama Rao and K. N. Ninan, Eur. Polym. J., 39, (2003) 1077

124. T. Adrain, W. Habel and P. Sartori, J. Prakt. Chem., 335 (1993) 288.

125. V. B. Van Aefferdan, W. Habel and P. Sartori, Chem. Ztg., 114 (1990) 309.

126. S. Packirisamy, G. Sundarajan, G. Ambadas and K. N. Ninan (manuscript under preparation).

127. G. J. Chen, C. E. Snyder Jr and K. C. Eapen, US Patent 6278011 (2001).

128. R. Corriu, B. Boury and C. Carpenter, Eur. Patent 3000862 (1989).

129. B. Boury, J. P. Robert, R. Corriu and W. E. Douglas, Chem. Mater., 3 (1991) 288.

Introduction 53

130. B. Boury, R. Corriu, D. Leclecq, D. Mutin, J. M. Planeix and A. Viour, Organometallics, 10 (1991) 1452.

131. H. J. Wu and L. V. Interrante, Macromolecules, 25 (1992) 1840.

132. V. Krishnan, R. Bindu, V. Chandrasekhar and V. S. R. Murthy, J. Am. Ceram. Soc., 85 (2002) 504.

133. K. Yoon and D. Y. Son, Macromolecules, 32 (1999) 5210.

134. J. Ohshita, A. Shinpo and A. Kunai, Macromolecules, 32 (1999) 5998.

135. Y. Li and D. Y. Son, Macromolecules, 32 (1999) 8768.

136. D. Seyferth, G. H. Wisemann, J. M. Schwark, Y. F. Yu and C. A. Poutase in Inorganic and Organometallic Polymers, M. Zeldin, K. J. Wynne and H. R. Allcock (Eds.), ACS Symp. Series, 360, 1988, p. 143.

137. D. Seyferth in Silicon-Based Polymer Science: A comprehensive Resourse, J. M. Zeigler and F. W. Gordon Fearon (Eds.), Advances in Chemistry Series 224, Am. Chem. Soc., Washington DC, 1990, p. 565.

138. W. Verbeek, Ger. Patent 2218960 (1973).

139. W. Verbeek, US Patent 3853567 (1974).

140. W. Verbeek, G. Winter and M. Mansmann, Ger. Patent 2243527 (1974).

141. G. Winter, W. Verbeek and M. Mansmann, US Patent 3892583 (1975).

142. D. Seyferth and G. H. Wisemann, Polym. Prep., 25 (1984) 10.

143. O. Funayama, T. Isoda, H. Kaya, T. Suzaki and Y. Tashiro, Polym. Prep., 32 (1991) 542.

144. D. Seyferth, G. H. Wisemann and C. Prudhomme, J. Am. Ceram. Soc., 66 (1983) C-13.

145. D. Seyferth and G. H. Wisemann, J. Am. Ceram. Soc., 67 (1984) C-132.

146. G. T. Burns, C. K. Saha, G. A. Zank and H. A. Freemann, J. Mater. Sci., 27 (1992) 2131.

147. C. Xu, C. Liu, Z. Zheng, Y. Li, Z. Zhang, S.Yang, and Z.Xie, J. Appl. Polym. Sci., 82 (2001) 2827.

148. X. Bao, P. P. Carpenter, M. J. Edirisinghe and D. D. Hall, Phil. Mag. Lett., 79 (1999) 453.

149. H. C. Kleebe, H. J. Franke and R. Riedel, J. Eur. Ceram. Soc., 20 (2000) 1355.

150. T. Rasul and D. Y. Son, J. Organomet. Chem., 655 (2002) 115.

151. S. Trassl, D. Suttor, G. Motz, E. Rossler and G. Ziegler, J. Eur. Ceram. Soc., 20 (2000) 215.

54 Chapter 1

152. Y. Sawai, Y. Iwamoto, S. Okuzaki, Y. Yasutomi, K. Kikuta and S. I. Hirano, J. Ceram. Soc. Jpn., 107 (1999) 1001.

153. E. Bacque, J. P. Pillot, M. Birot, J. Dunogues, G. Bougeois and M. Petraud, J. Organomet. Chem., 481 (1994) 167.

154. A. Kienzle, A. Obermayer, A. Simon, R. Riedel and F. Aldinger, Chem. Ber., 126 (1993) 2569.

155. M. Weinmann, R. Haug, J. Bill, F. Aldinger, J. Schuhmacher and K. Muller, J. Organomet. Chem., 541 (1997) 345.

156. D. A. Loy and K. J. Shea, Chem. Rev., 95 (1995) 1431.

157. G. Zhi, L. H. Cho, L. Wang, H. Toghiani and C. U. Pittmann Jr., J. Polym. Sci., Polym. Chem. Ed., 43 (2005) 355.

158. S. G. Kim, J. Choi, R. Tamaki and R. M. Laine, Polymer, 46 (2005) 4514.

159. K. Kamiya, O. Makoto and T. Yoko, J. Non-Cryst. Solids, 83 (1986) 208.

160. D. A. White, S. M. Oleff, R. D. Boyer, P. A. Budinger and J. R. Fox, Adv. Ceram. Mater., 2 (1987) 45.

161. A. Schiavon, S. U. A. Redondo, S. R. O. Pina and I. V. P. Yoshida, J. Non-Cryst. Solids, 304 (2002) 92.

162. F. I. Hurwitz, P. Heimann and S. C. Farmer, J. Mater. Sci., 28 (1993) 6622.

163. C. G. Wei, C. R. Kennedy and L. A. Harris, Am. Ceram. Soc. Bull., 63 (1984) 1054.

164. G. T. Burns, R. B. Taylor, Y. Xu, A. Zangvil and G. A. Zank, Chem. Mater., 4 (1992) 1313.

165. G. M. Renlund, S. Prochaska, R. H. Doremus, J. Mater. Res., 6 (1991) 2716.

166. G. M. Renlund, S. Prochaska, R. H. Doremus, J. Mater. Res., 6 (1991) 2723.

167. W. H. Atwell, G. T. Burns and C. K. Saha, US Patent 4888376 (1989).

168. K. J. Negita, J. Am. Ceram. Soc., 69 (1986) C308.

169. F. Babonneau, K. Thorne and J. D. Mackenzie, Chem. Mater., 1 (1989) 554.

170. P. Colombo and M. Modesti, J. Sol-Gel Sci. Tech., 14 (1999) 103.

171. G. D. Soraru, G. D. Andrea, R. Campostrini, F. Babonneau and G. Mariotto, J. Am. Ceram. Soc., 78 (1995) 379.

172. E. Radovanovic, M. F. Gozzi, M. C. Goncalves and I. V. P. Yoshida, J. Non-Cryst. Solids, 248 (1999) 37.

173. C. J. Plummer, L. Garamszegi, T. Q. Nguyen and M. Rodlert, J. Mater. Sci., 37 (2002) 4819.

Introduction 55

174. A. Kaindl, W. Lehner, P. Greil and D. J. Kim, Mater. Sci. Eng. A, 260 (1999) 101.

175. O. Dernovsek, J. C. Bressiani, A. H. A. Bressiani, W. Acchar and P. Greil, J. Mater. Sci., 35 (2000) 2201.

176. T. Michalet, M. Parlier, A. Addad and R. Duclos, Ceram. Int., 27 (2001) 315.

177. R. Melcher, P. Cromme, M. Scheffler and P. Greil, J. Am. Ceram. Soc., 86 (2003) 1211.

178. Q. We, E. Pippel, J. Woltersdorf, M. Scheffler and P. Greil, J. Mater. Chem., 73 (2002) 281.

179. V. Belot, R. J. P. Corriu, D. Leclercq, P. H. Mutin and A. Vioux, J. Polym. Sci., Polym. Chem. Ed., 30 (1992) 613.

180. J. Marchi, A. H. A. Bressiani and J. C. Bressiani, Mater. Res., 4 (2001) 231.

181. R. Melcher R. P. Cromme, M. Scheffler and P. Greil, J. Am. Ceram. Soc., 86 (2003) 1211.

182. W. H. Philipp, NASA TM-102489, 1990.

183. R. T. Paine and C. K. Narula, Chem. Rev., 90 (1990) 73.

184. C. K. Narula, R. T. Paine and R. Schaeffer in Inorganic and Organometallic Polymers, M. Zeldin, K. J. Wynne and H. R. Allcock (Eds.), ACS Symp. Series 360, Am. Chem. Soc., Washington DC, 1988, p. 378.

185. T. Taniguchi, Y. Kimura and K. Yamamoto, Ger. Offen DE 3528394 (1986).

186. P. J. Fazen, J. S. Beck, A. T. Lynch, E. E. Remsen and L. G. Sneddon, Chem. Mater., 2 (1990) 96.

187. L. G. Sneddon, M. G. L. Mirabelli, A. T. Lynch, P. J. Fazen, K. Su and J. S. Beck, Pure & Appl. Chem., 63 (1991) 407.

188. R. T. Paine and L. G. Sneddon in Inorganic and Organometallic Polymers II, P. W. Neilson, H. R. Allcock and K. J. Wynne (Eds.), ACS Symp. Series 572, Am. Chem. Soc., Washington DC, 1994, p. 358

189. C. K. Narula, R. Schaeffer, A. Datye and R. T. Paine, Inorg. Chem., 28 (1989) 4053.

190. Y. Kimura, Y. Kubo and N. Hayashi, J. Inorg. Organomet. Polym., 2 (1992) 231.

191. K. J. L. Paciorek, D. A. Harris and R. H. Kratzer, J. Polym. Sci., Polym. Chem. Ed., 24 (1986) 173.

192. B. A. Bender, R. Rice and J. R. Spann, J. Am. Ceram. Soc., 70 (1987) C-58.

193. C. K. Narula, R. Schaeffer and R. T. Paine, J. Am. Chem. Soc., 109 (1987) 5556.

56 Chapter 1

194. R. T. Paine, J. Inorg. Organomet. Polym., 2 (1992) 183.

195. K. J. L. Paciorek, W. K. Schidt, D. H. Harris, R. H. Kratzer and K. J. Wynne in Inorganic and Organometallic Polymers, J. Zeldin, K. J. Wynne, H. J. Allcock (Eds.), ACS Symp. Series 360, Am. Chem. Soc., Washington DC, 1988, p. 392.

196. K. J. L. Paciorek, S. R. Masud and R. H. Kratzer, Chem. Mater., 3 (1991) 88.

197. L. Maya in Better Ceramics Through Chemistry, C. J. Brinker, D. E. Clark and D. R. Ulrich (Eds.), Mater. Res. Soc. Symp. Proc., 121, Pennsylvania, 1988, p. 455.

198. L. Maya, Appl. Organomet. Chem., 10 (1996) 175.

199. A. T. Lynch and L. G. Sneddon, J. Am. Chem. Soc., 109 (1987) 5867.

200. A. T. Lynch and L. G. Sneddon, J. Am. Chem. Soc., 111 (1989) 620.

201. K. Su, E. E. Remsen, H. M. Thompson and L. G. Sneddon, Polym. Prep., 32 (1991) 481.

202. J. A. Perdigon-Melon, A. Auroux, J. M. Guil and B. Bonnetot, Stud. Surf. Sci. Catal.,143 (2002) 227.

203. B.Toury, P. Miele, D. Cornu, H. Vincent and J. Bouix, Adv. Funct. Mater., 12 (2002) 228.

204. R. Schaeffer, J. Am. Chem. Soc., 79 (1957) 1006.

205. L. Barton, T. Onak, R. J. Rammel and S. G. S. Gmel in Hand book of Inorganic Chemistry 54, K. Niedenzu and K. C. Buschbeek (Eds.), Springer Verlag, Berlin, 1979, p. 122.

206. G. W. Parshall, US Patent 3035949 (1962).

207. D. Seyferth and W. S. Rees Jr., Chem. Mater., 3 (1991) 1106.

208. S. Packirisamy, D. Schwam and M. H. Litt, J. Mater. Sci., 30 (1995) 308.

209. S. Packirisamy, D. Schwann and M. H. Litt, Polym. Prep., 34 (1993) 197.

210. R. E. Johnson, US Patent 4810436 (1986).

211. J. R. Reiner and H. A. Schroeder, US Patent 3141856 (1964).

212. D. Seyferth and W.S. Rees Jr., Mater. Res. Soc. Symp. Proc., 121 (1988) 449.

213. W. S. Rees Jr. and D. Seyferth, J. Am. Ceram. Soc., 71 (1988) C194.

214. M. J. Pender, K. M. Forsthoefel and L. G. Sneddon, Pure & Appl. Chem., 75 (2003) 1287.

215. W. K. Seok and L. G. Sneddon, Bull. Korean Chem. Soc., 19 (1998) 1398.

216. L. G. Sneddon and J. Mark, US Patent 6478994 (2002).

Introduction 57

217. K. Forsthoefel and L. Sneddon, J. Mater. Sci., 39 (2004) 6043.

218. R. E. Johnson, US Patent 4810436 (1989).

219. R. E. Johnson, US Patent 4832895 (1989).

220. R. E. Johnson, US Patent 4946919 (1990).

221. D. Seyferth and W. S. Rees, US Patent 4871826 (1989).

222. M. G. L. Mirabelli and L. G. Sneddon, J. Am. Chem. Soc., 110 (1988) 3305.

223. M. G. L. Mirabelli, A. T. Lynch and L. G. Sneddon, Solid State Ionics, 32/33 (1988) 655.

224. H. Wada, S. Ito, K. Kurado and C. Kato, Chem. Lett., 6 (1985) 691.

225. H. Steinberg, Organoboron Chemistry, Vol. 1, Boron-Oxygen and Boron-Sulphur Compounds, Interscience, New York, 1964, Chapter 5.

226. H. Wada, K. Nojima, K. Kuroda and C. Kato, Yogyo Kyosaishi, 95 (1987) 130.

227. S. Mondal, D. Bhattacharya and A. K. Banthia, Mater. Lett., 44 (2000) 113.

228. Y. J. Tian, J. L. He, D. L. Yu, D. C. Li, G. T. Zou, X. R. Jia, L. X. Chen and O. Yanagisawa, Radiation Effects and Defects In Solids, 157 (2002) 245.

229. S. Mondal and A. K. Banthia, J. Eur. Ceram. Soc., 25 (2005) 287.

230. R. Riedel in Materials Science and Technology: A Comprehensive Treatment, R. W. Cahn, P. Haasen and E. J. Kramer (Eds.), Advanced Ceramics from Inorganic Polymers Vol. 17B, VCH Verlagsgesell Schaft mbh, Federal Republic of Germany, 1996, Chap. 11.

231. R. Riedel, J. Bill and A. Kienzle, Appl. Organomet. Chem., 10 (1996) 241.

232. R. Riedel, A. Kienzle, W. Dressler, L. Ruwisch, J. Bill and F. Aldinger, Nature, 382 (1996) A796.

233. S. Ricitiello, M. S. Hsu and T. Chen, US. Patent 4676962 (1987).

234. M. T. S. Hsu, T. S. Cha and S. R. Riceitiello, J. Appl. Polym. Sci., 42 (1991) 851.

235. M. T. S. Hsu, T. S. Cha and S. R. Riceitiello, Polym. Prep., 27 (1986) 261.

236. V. P. Gutenberger, W. Habel, C. Novers and P. Sartori, J. Organomet. Chem., 453 (1993) 1.

237. R. A. Sundar and T. M. Keller, Polym. Prep., 37 (1996) 301.

238. R. A. Sundar and T. M. Keller, Macromolecules, 29 (1996) 3647.

239. K. L. J. Henderson Jr. and T. M. Keller, Macromolecules, 27 (1994) 1660.

240. R. N. Grimes, Carboranes, Academic Press, New York, 1970.

241. T. L. Heying, S. Papetti and O. G. Schaffling, US Patent 3388090 (1968).

58 Chapter 1

242. S. Papetti, B. B. Schaeffer, A. P. Grey and T. L. Heying, J. Polym. Sci., Polym. Chem. Ed., 4 (1966) 1623.

243. T. L. Heying, S. Papetti and O. G. Schaffling, US Patent 3388091 (1968).

244. T. L. Heying, S. Papetti and O. G. Schaffling, US Patent 3388092 (1968).

245. H. Beall in Boron Hydride Chemistry, E. L. Muetterties (Ed.), Academic Press, New York, 1975, p. 338.

246. B. E. Walker Jr., R. W. Rice, P. F. Becher, B. A. Bender and W. S. Coblenz, Am. Ceram. Soc. Bull., 62 (1983) 916.

247. H. Zheng, K. Thorne, J. D. Mackenzie, X. Yang and M. F. Hawthorne, Mater. Res. Soc. Symp. Proc. 249 (1992) 15.

248. J. Kulig, G. Jefferis and M. H. Litt, Polym. Mater. Sci. Eng., 61 (1989) 219.

249. J. Kulig, D. Schwam and M. H. Litt in Inorganic and Metal Containing Polymeric Materials, J. Sheats (Ed.), Plenum Press, New York, 1990, p. 225.

250. L. M. Niebylski, US Patent 4910173 (1990).

251. L. M. Niebylski, US Patent 4921925 (1990).

252. K. Su, E. E. Remsen, G. A. Zank and L. G. Sneddon, Chem. Mater., 5 (1993) 547.

253. K. Su, E. E. Remsen, G. A. Zank and L. G. Sneddon, Polym. Prep., 34 (1993) 334.

254. T. Wideman, E. Cortz, E. E. Remsen, G. A. Zank, P. J. Carrol and L. G. Sneddon, Chem. Mater., 10 (1998) 2218.

255. D. Seyferth, H. Pleino, W. S. Rees Jr. and K. Buhner in Fronteirs of Organosilicon Chemistry, A. R. Bassindale and P.P. Gaspar (Eds.), Royal Society of Chemistry, Cambridge, 1991, p. 15.

256. O. Funayama, T. Kato, Y. Tahiro and T. Isoda, J. Am. Ceram. Soc., 76 (1993) 717.

257. O. Funayama, I. Aoki and T. Isoda, J. Ceram. Soc. Jpn., 104 (1996) 355.

258. M. Weinmann and F. Aldinger in Precursor-Derived Ceramics, J. Bill, F. Wakai and F. Aldinger (Eds.), Wiley-VCH, Wemheitn, Germany, 1999, p. 83.

259. M. Weinmann, M. Horz, F. Berger, A. Muller, K. Muller and F. Aldinger, J. Organomet. Chem., 659 (2002) 29.

260. M. Weinmann, H. J. Seifert and F. Aldinger in Contemporary Boron Chemistry, M. G. Davidson, A. K. Hughes, T. B. Marder and K. Wade (Eds.), The Royal Society of Chemistry, Cambridge, 2000, p. 88.

261. Y. C. Zeng, X. F. Chun, C. S. Yong, D. L. Xiao and Y. X. Jia, J. Appl. Polym. Sci., 94 (2004) 105.

Introduction 59

262. M. A. Schiavon, G. D. Soraru, I. Valeria and I. V. P. Yoshida, J. Non-cryst. Solids, 348 (2004) 156.

263. M. A. Schiavon, G. D. Soraru, I. Valeria and I. V. P. Yoshida, J. Non-cryst. Solids, 304 (2002) 76.

264. H. P. Baldus and G. Passing in Advanced Structural Fibers and Composites, P. Vincenzini (Ed.), Techna, 1995, p. 125.

265. H. P. Baldus, M. Jansen and O. Wagner, Key. Eng. Mater., 89 (1994) 75.

266. R. Riedel, Naturwissenschaften, 82 (1995) 12.

267. L. J. Henderson Jr. and T. M. Keller in Inorganic and Organometallic Polymers II, P. Wisien Neilson, H. R. Allcock and K. J. Wynne (Eds.), ACS Symp. Series 572, American Chemical Society, Washington, 1994, p. 416.

268. L. J. Henderson Jr. and T. M. Keller, Macromolecules, 27 (1994) 1660.

269. D. Bucca and T. M. Keller, J. Polym. Sci., Polym. Chem. Ed., 35 (1997) 1033.

270. D. Bucca and T. M. Keller, J. Polym. Sci., Polym. Chem. Ed., 37 (1999) 4356.

271. R. Jansen and M. Kroschel, Zeitschrift Fur Anorganische Und Allgemeine Chemie, 626 (2000) 1634.

272. M. F. Lappert and G. J. Leigh in Developments in Inorganic Polymer Chemistry, Elsevier Publishing Company, 1962, p. 225.

273. S. Yajima, K. Okamura, J. Hayashi and T. Shishido, US Patent 4152509 (1979).

274. M. G. Voronkov and N. V. Zgonik, Zhur. Obshchei Khim., 27 (1957) 1476.

275. I. Kijima, T. Yamamoto and Y. Abe, Bull. Chem. Soc. Jpn., 44 (1971) 3193.

276. G. Ambadas, S. Packirisamy and K. N. Ninan, J. Mater. Sci. Lett., 21 (2002) 1003.

277. H. Kobayashi, US Patent 4228270 (1980).

278. S. Hoshii, A. Kojima, M. Shimoda, S. Otani, T. Satou, Y. Nakaido and Y. Hasegawa, Tanso, 161 (1994) 23.

279. S. Hoshii, A. Kojima, H. Endou, S. Otani, T. Satou, Y. Nakaido and Y. Hasegawa, Tanso, 156 (1993) 29.

280. S. Hoshii and A. Kojima, J. Mater. Res., 11 (1996) 2536.

281. B. E. Yoldas, J. Mater. Sci., 12 (1977) 123.

282. A. Kasgoz and M. Kuramata, J. Ceram. Soc. Jpn., 97 (1989) 1432.

60 Chapter 1

283. M. A. Beckett, P. Martin, R. Hankey and K. S. Varma, Chem. Commun., (2000) 1499.

284. A. Kasgoz, M. Kuramata, T. Misono and Y. Abe, J. Polym. Sci., Polym. Chem. Ed., 32 (1994) 1049.

285. A. Kasgoz , M. Kuramata and Y. Abe, J. Mater. Sci., 34 (1999) 6137.

286. J. P. Pillot, M. Birot, J. Dunogues, Y. Lurent, P. L. Haridon and L. Bois, US Patent 6180809b1 (2001).

287. J. E. Mark, Heterogeneous Chem. Rev., 3 (1986) 307.

288. C. Zha, G. R. Atkins and A. F. Masters, J. Sol-Gel Sci. Tech., 13 (1998) 103.

289. B. Li, Z. Yue, J. Zhou, Z. Gui and L. Li, Mater. Lett., 54 (2002) 25.

290. R. P. Alonso, J. Rubio, F. Rubio and J. L. Oteo, J. Sol-Gel Sci. Tech., 26 (2003) 195.

291. D. Boschel and H. Roggendorf, J. Sol- Gel Sci. Tech., 25 (2002) 191.

292. I. M. Thomas, US Patent 4030938 (1977).

293. M. Nogami and Y. Moriya, J. Non-Cryst. Solids, 48 (1982) 359.

294. N. Tohge, A. Matsuda and T. Minami, J. Am. Ceram. Soc., 70 (1987) 13.

295. M. A. Villegas and J. M. F. Navarro, J. Mater. Sci., 23 (1988) 2464.

296. A. D. Irwin, J. S. Holmgren, T. W. Zerda and J. Jonas, J. Non-Cryst. Solids, 89 (1987) 191.

297. A. D. Irwin, J. S. Holmgren, T. W. Zerda and J. Jonas, J. Non-Cryst. Solids, 101 (1988) 249.

298. Y. Abe, T. Gunji, K. Kimata, M. Kuramata, A. Kasgoz and T. Misono, J. Non-Cryst. Solids, 121 (1988) 21.

299. G. D. Soraru, N. Dallabona, C. Gervais and F. Babonneau, Chem. Mater., 11 (1999) 910.

300. G. D. Soraru, F. Babonneau, C. Gervais and N. Dallabona, J. Sol-Gel Sci. Tech., 18 (2000) 11.

301. C. Gervais, F. Babonneau, N. Dallabona and G. D. Soraru, J. Am. Ceram. Soc., 84 (2001) 2160.

302. K. H. Yang and A. J. Woo, Bull. Korean Chem. Soc., 17 (1996) 696.

303. S. Packirisamy, G. Ambadas, P. K. Narendranath and K. N. Ninan, Indian Patent Appl. No. 798/MAS/99.

304. S. Yajima, T. Shishido and M. Hamada, Nature, 266 (1977) 522.

305. S. Yajima, K. Okamura and Y. Hasegawa, Ger. Often 284652 (1979).

306. H. Hashimoto, A. Ishiyama and M. Yoda, Jpn.Patent 3147206 (1991).

Introduction 61

307. Y. Okamura, K. Kumagai and S. Mori, Jpn.Patent 2088443 (1990).

308. G. T. Burns and G. A. Zank, Eur. Patent 0437934 (1991).

309. S. Yajima, K. Okamura, T. Shishido and Y. Hasegawa, US Patent 4242487 (1980).

310. K. Sunada, Jpn. Patent 2004277204 (2004).

311. W. Kalchauer, W. Graf and B. Pachaly, US Patent 5098747 (1992)

312. S. Yajima, K. Okamura and T. Shishido, US Patent 4361679 (1982).

313. M. Morita, E. Hosokawa and K. Arahara, US Patent 4405687 (1983).

314. E. Hosokawa and H. Hashimoto, US Patent 4735858 (1988).

315. L. M. Niebylski, US Patent 4970282 (1990).

316. A. Kasgoz, M. Kuramata, T. Misono and Y. Abe, Nippon Seramikkusu Ronbun-Shi, 97 (1989) 1432.

317. H. Dislich, J. Non-Cryst. Solids, 73 (1985) 599.

318. W. G. French and A. D. Pearson, Appl. Phys. Lett., 23 (1973) 338.

319. S. H. Wemple and D. A. Pinnow, J. Appl. Phys., 44 (1973) 5432.

320. D. Kato, J. Appl. Phys., 47 (1976) 2050.

321. Y. J. Misawa, J. Electrochem. Soc., 131 (1984) 1862.

322. Y. J. Misawa, J. Electrochem. Soc., 131 (1984) 2618.

323. Nichias Co. Jpn Kokai Tokkvo Koho, JP 60 167 924 [85 167 924].

324. K. Tomida, N. Miyashita and H. Hashimoto, Showa Electric Wire & Cable LTD's Review, 39 (1989) 321.

325. Y. Kiuchi and N. Sukegawa, Showa Electric Wire & Cable LTD's Review, 41 (1991) 79.

326. Y. Fukuda, Y. Kaneko and M. Maki, Jpn. Kokai, Tokkyo Koho, JP 60 188 758 [85 188 758].

327. S.Yajima, K. Okamura and T. Shishido, US Patent 4248814 (1981).

328. C. R. Bearinger, R. C. Camilletti, G. Chandra, T. E. Gentle and L. A. Haluska, US Patent 5904791 (1999).

329. K. Hiroshi, Jpn. Patent 54088247 (1979).

330. K. Hiroshi, Jpn. Patent 54083100 (1979).

331. S. Tatsuki, S. Inubushi and M. Yoshikawa, Jpn. Patent 61231020 (1989).

332. R. Lagarde and N. Bouverot, US Patent 4690967 (1987).

333. S. Packirisamy, G. Ambadas and K. N. Ninan, Prog. Org. Coat. (to be communicated).

62 Chapter 1

334. K. J. Wynne and R. W. Rice, Annu. Rev. Mater., 14 (1984) 297.

335. R. West and J. Maxka in Inorganic and Organometallic Polymers , ACS Symp. Series 360, M. Zeldin and K. J. Wynne (Eds.), Am. Chem. Soc., Washington DC, 1988, p. 66.

336. S. Yajima, K. Okumara, T. Shishido and Y. Hasegawa, Ger. Patent 2945650 (1980).

337. M. R. Mucalo and N. B. Milestone, J. Mater. Sci., 29 (1994) 5934.

338. M. R. Mucalo, N. B. Milestone, I. C. Vickridge and M. V. Swain, J. Mater. Sci., 29 (1994) 4487.

339. S. Yajima, K. Okumara and J. Hayashi, Chem. Lett., 4 (1975) 1209.

340. S. Yajima, Y. Hasegawa and M. Imura, J. Mater. Sci., 13 (1978) 3567.

341. W. Toreki, G. J. Choi, C. D. Batich, M. D. Sacks and M. Saleem, Ceram. Eng. Sci. Proc., 13 (1992) 198.

342. Y. Yang, Y. Liu, Z. Tan, S. Yang, Y. Lu and C. Feng, J. Mater. Sci., 26 (1991) 5167.

343. Y. Hasegawa and K. Okamura, J. Mater. Sci., 18 (1983) 3633.

344. M. K. Meyer, M. Akine, S. I. Maghsoodi, X. Zhang and T. J. Barton, Ceram. Eng. Sci. Proc., 12 (1991) 1019.

345. K. Okumara, M. Sato, Y. Hasegawa and T. Amano, Chem. Lett., 13 (1984) 2059.

346. O. Funayama, H. Nakahama, M. Okada, M. Okumara and T. Isoda, J. Mater. Sci., 30 (1995) 410.

347. M. Narisawa, M. Nishioka and K. Okamura, K. Oka and T. Dohmaru, Advanced SiC/SiC ceramic composites: Developments and Applications in Energy Systems, Ceramic Transactions, 144 (2002) 173.

348. M. Takeda, A. Urano, J. I. Sakamoto and Y. Imai, J. Nuc. Mater., 258 (1998) 1594.

349. A. Idesaki, M. Narisawa, K. Okamura, M. Sugimoto, T. Seguchi and M. Itoh, Key Eng. Mater., 159 (1999) 107.

350. X. Li, C. Feng, Y. Wang, Y. Zhao and Y. Song, High Tech. Lett., 8 (1998) 41.

351. M. Narisawa, T. Hasegawa, K. Okamura, M. Itoh, T. Apple, K. V. Moraes and L. V. Interrante, J. Mater. Res., 17 (2002) 214.

352. W. Yifei, Z. Peng, S. Yongcai and F. Chunxiang, Aerospace Materials and Technology, 31 (2001) 24.

353. F. Cao, D. P. Kim and X. D. Li, J. Mater. Chem., 12 (2002) 1213.

Introduction 63

354. M. Jansen, J. M. Jaschke and T. Jaschke in High Performance Non-Oxide Ceramics I, Structure and Bonding, Springer-Verlag, Berlin, M. Jansen (Ed.) 101, 2002, p. 137.

355. P. Miele, B.Toury, D. Cornu and S. Bernard, J. Organomet. Chem., 690 (2005) 2809.

356. G. Zeigler, Macromol. Chem., Macromol. Symp., 50 (1991) 107.

357. S. Yajima, T. Shishido, H. Kayano, K. Okamura, M. Omori and J. Hayashi, Nature, 264 (1976) 238.

358. K. Nihara, T. Yamamoto, J. Arima, R. Takemoto, K. Sugama, R. Watanabe, T. Nishikawa and M. Okkamura in Ultrastructure Processing of Advanced Ceramics, J. D. MacKenzie and D. R. Ulrich (Eds.), Wiley Interscience Publication, 1988, p. 547.

359. S. T. Schwab, C. R. Blanchard and R. C. Graef, J. Mater. Sci., 29 (1994) 6320.

360. S. R. Su in Synthesis and Processing of Ceramics: Scientific Issues, W. E. Rhine, T. M. Shaw, R. J. Gottschall and Y. Chen (Eds.), Mater. Res. Soc., 249 (1992) 383.

361. K. K. Chawla, Ceramic Matrix Composites, Chapman and Hall, London (1993).

362. R. Gadow and F. Kern, Adv. Eng. Mater., 14 (2002) 883.

363. P. Greil, J. Am. Ceram. Soc., 78 (1995) 835.

364. J. E. French, in Handbook of Continuous Fiber Ceramic Composites, American Ceramic Society, 269, 1996.

365. F. I. Hurwitz, J. Z. Gyekenyesi, and P. J. Conroy, Ceram. Eng. Sci. Proc., 10 (1989) 750.

366. K. Sato, H. Morozumi, A. Tezuka, O. Funayama, and T. Isoda, High Temperature Ceramic Matrix Composites II, A. G. Evans and F. W. Zok, (Eds.), Am. Ceram. Soc., 199, 1995.

367. M. F. Gonon, G. Fantozzi, M. Murat, and J. P. Disson, J. Eur. Ceram. Soc., 15 (1995) 185.

368. R. W. Rice, Porosity of ceramics, Marcel Dekker Inc., (1998).

369. J. S. Woyansky, C. E. Scott and W. P. Minnear, Am. Ceram. Soc. Bull., 71 (1992) 1674.

370. E. J. A. E. Williams and J. R. G. Evans, J. Mater. Sci., 31 (1996) 559.

371. P. Sepulveda and J. G. P. Binner, J. Eur. Ceram. Soc., 19 (1999) 2059.

372. L. E. Kolaya and N. Lewis, 21st Annual Conference and Expo on Composites, Advanced Ceramics, Materials and Structures, Am. Ceram. Soc., Cocoa beach, Florida, 1997, p. 9.

64 Chapter 1

373. H. Q. Ly, R. Taylor and R. J. Day, J. Mater. Sci., 36 (2001) 4027.

374. M. Kotani, T. Inoue, A. K. K. Okamura and Y. Katoh., Comp. Sci. & Tech., 62 (2002) 2179.

375. K. Schwartzwalder, H. Somers and A. V. Somers, US Patent 3090094 (1963).