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Prog. Polym. Sci. 31 (2006) 983–1008

www.elsevier.com/locate/ppolysci

Addition polymers from natural oils—A review

Vinay Sharma, P.P. Kundu�

Department of Chemical Technology, Sant Longowal Institute of Engineering and Technology, Sangrur, Punjab 148106, India

Received 23 January 2006; received in revised form 14 September 2006; accepted 15 September 2006

Abstract

Emerging technological knowledge is leading research into new ventures. One such is the conversion of natural oils to

polymers to augment the use of petroleum products as the source of polymeric raw materials. Natural oils, such as vegetable

oils, now mainly used in the food industry, offer alternatives, and recent research has studied new routes of synthesis of

polymers from natural oils. This review paper discusses the synthesis and characterization of new polymers from different

natural oils such as soybean, corn, tung, linseed, castor, and fish oil. The effects of different levels of unsaturation in the

natural oils and various types of catalysts and comonomers on the properties of copolymers are considered.

r 2006 Elsevier Ltd. All rights reserved.

Keywords: Natural oils; Dynamic mechanical analysis; Cross-linking; Polymerization; Drying oil; Glass transition temperature

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 984

2. Polymers from natural oils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 985

2.1. Soybean oil polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 985

2.1.1. Unmodified soybean oil polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 985

2.1.2. Modified soybean oil polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 992

2.2. Fish oil polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 994

2.3. Corn oil polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 995

2.4. Tung oil polymers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 996

2.5. Linseed oil polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 998

2.5.1. Natural linseed oil polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 998

2.5.2. Epoxidized linseed oil polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1002

2.6. Castor oil polymers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1003

2.7. Polymers from other oils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1004

3. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1005

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1006

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1006

e front matter r 2006 Elsevier Ltd. All rights reserved.

ogpolymsci.2006.09.003

ing author. Tel.: +9116 7283606; fax: +91 16 7283657.

ess: ppk923@yahoo.com (P.P. Kundu).

ARTICLE IN PRESSV. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008984

1. Introduction

In recent years natural oils have attractedrenewed attention as raw materials for the prepara-tion of resins and polymeric materials, to replace oraugment the traditional petro-chemical based poly-mers and resins. Natural oils such as linseed andtung oil have long found various uses in the paintand varnishes industries. These oils have tradition-ally been used in organic coatings either as resins oras a raw material for the preparation of resins.Soybean oil, safflower oil, sunflower oil and canolaoil have also been used in polymerizations.

Natural oils are tri-glyceride esters of fatty acids,the general structure of which is shown in Fig. 1.Triglycerides comprise three fatty acids joined by aglycerol center [1]. Most of the common oil containsfatty acids that vary from 14 to 22 carbons inlength, with 1–3 double bonds. The fatty aciddistribution of several common oils is shown inTable 1 [1]. In addition, there are some oils comprisefatty acids with other types of functionalities (e.g.,

O

O

O

O

O

O

glycerol centerfatty acid chain

three ester bonds

Fig. 1. The triglyceride chain containing three fatty acid chains joined b

42: 1569 r Elsevier Science Ltd., [10].

Table 1

Main fatty acid contents in different oils

Fatty acid [#C: #DB�] Canola oil Corn oil Cotton

Palmitic 16:0 4.1 10.9 21.6

Stearic 18:0 1.8 2.0 2.6

Oleic 18:1 60.9 25.4 18.6

Linoleic 18:2 21.0 59.6 54.4

Linolenic 18:3 8.8 1.2 0.7

a-elaeostearic acid — — — —

Average #DB/triglyceride. — 3.9 4.5 3.9

Reproduced with the permission from J Appl Polym Sci 2001; 82: 703�#C stands for number of carbon atoms in chain and #DB stands fyFish oils tend to contain a high double bond content; for exampl

contained a fatty acid (ethyl ester) composition with 8.90% having no

EPA or DPA and 24.72% (DHA) having six double bonds [29].

epoxies, hydroxyls, cyclic groups and furanoidgroups) [2]. It is apparent that on a molecular level,these oils are composed of many different types oftriglyceride, with numerous levels of unsaturation.In addition to their application in the food industry,triglyceride oils have been used for the productionof coatings, inks, plasticizers, lubricants and agro-chemicals [3–9]. In general, drying oils (these canpolymerize in air to form a tough elastic film) arethe most widely used oils in these industries,although the semi-drying oils (these partially hardenwhen exposed to air) also find use in someapplications. The polymers obtained from naturaloils are biopolymers in the sense that they aregenerated from renewable natural sources; they areoften biodegradable as well as non-toxic.

Some biopolymers obtained from natural oils areflexible and rubbery. Generally, they are preparedas cross-linked copolymers. Bacterial polyesters areobtained from a large number of bacteria whensubjected to metabolic stress. The cross-linkingprocess for unsaturated bacterial polyester is shown

oleic acid chain

linoleic acid chain

linolenic acid chain

y a glycerol center. Reprinted with permission from Polymer 2001;

seed oil Linseed oil Olive oil Soybean oil Tung oil Fish oily

5.5 13.7 11.0 — —

3.5 2.5 4.0 4 —

19.1 71.1 23.4 8 18.20

15.3 10.0 53.3 4 1.10

56.6 0.6 7.8 — 0.99

— — — 84 —

6.6 2.8 4.6 7.5 3.6

r John Wiley and Sons, Inc. [1].

or the number of double bonds in that chain.

e, the composition of a Norway fish oil examined in one study

double bonds, 6.03% having four double bonds, 37.25% having

ARTICLE IN PRESSV. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008 985

in Fig. 2, describing the cross-linking of theunsaturated bacterial polyesters prepared fromsoybean oily fatty acids. It is observed that cross-linking occurs in at least two polyester chain doublebonds. Scheme 1 describes the representativeprocess of cationic copolymerization of the trigly-ceride oil with styrene and divinylbenzene in thepresence of a modified boron trifluoride diethyletherate. Scheme 2 shows the oligomerization of amodified acrylated epoxidized soybean oil (AESO)with reagents selected to stiffen the polymer chain.Scheme 2(a) shows the oligomerization of an AESO

CH CH2 C

O

O CH CH2 C

O

CH CH2 C

O

O CH CH2 C

O

Fig. 2. The cross-linking process of bacterial polyester obtained from so

Bull 2001; 46: 393 r Springer-Verlag, Inc. [24].

CO2

CO2

CO2

CH

CH

CH

CH

CH

CH

+

m

OO

C CO O

CH2

CH HC CH CH

Scheme 1. The proposed process of cross-linking of natural oil with

Reprinted with the permission from J Appl Polym Sci 2003; 90: 1832 r

with cyclohexane dicarboxylic acid. Scheme 2(b)shows the oligomerization with maleic acid, whichintroduces more double bonds in the oligomers.

2. Polymers from natural oils

2.1. Soybean oil polymers

2.1.1. Unmodified soybean oil polymers

Polymers derived from soybean oils have beenextensively investigated by Larock et al. [10–15];soybean oils are biodegradable vegetable oil, readily

O HC CH2 C

O

O

O CH CH2 C

O

O

ybean oily fatty acids. Reprinted with the permission from Polym

+

n

H2C C

O

CH CH

CH CH2

CH CH2

CH

m

styrene and divinylbenzene in presence of modified initiator.

Wiley Periodicals, Inc. [30].

ARTICLE IN PRESS

Scheme 2. The modification of acrylated epoxidized soybean oil (AESO) shown using cyclohexane dicarboxylic anhydride or maleic

anhydride. These AESOs were cured with styrene or other comonomers. Reprinted with the permission from J Appl Polym Sci 2001; 82:

707 r John Wiley and Sons, Inc. [1].

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008986

available in bulk; specification of soybean oils usedby the Larock group are reported in Table 2.Natural soybean oil possesses a triglyceride struc-ture with highly unsaturated fatty acid side chains.The 1H NMR spectra of some example oils areshown in Fig. 3. The unsaturation in these oilsmakes them ideal monomers for the preparation of

various polymers. Cationic copolymerization ofregular soybean oil, low saturated soybean oil orconjugated low saturated soybean oil with styreneand divinylbenzene leads to various copolymers.These copolymers have been characterized byvarious techniques, including dynamic mechanicalanalysis (DMA), thermogravimetric analysis

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Fig. 3. The 1H NMR spectra of different soybean oils. (a) regular soybean oil, (b) low saturated soybean oil and (c) conjugated low

saturated soybean oil. Reprinted with permission from J Appl Polym Sci 2001; 80: 660 r John Wiley and Sons, Inc. [11].

Table 2

The composition of the soybean oils used for the preparation of copolymers

Soybean oil CQQC Fatty acidsb

Type No.a C16:0 C18:0 C18:1 C18:2 C18:3

Regular soybean oil Non-conjugated 4.5 10.5 3.2 22.3 54.4 8.3

Low saturated soybean oil Non-conjugated 5.1 5.0 3.0 20.0 64.0 9.0

Conjugated saturated soybean oil Conjugated 5.1 5.0 3.0 20.0 64.0 9.0

Reproduced with the permission from J Polym Sci: Part B: Polym Phys 2000; 38: 2722 r John Wiley and Sons, Inc. [12].aThe average number of carbon-carbon double bonds was calculated by 1H NMR spectral analysis.bFor example, C18:2 represent the fatty acid (ester) that possesses 18 carbons and 2 CQQC bonds.

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008 987

(TGA), differential scanning calorimetry (DSC),scanning electron microscopy (SEM) and thermalmechanical analysis (TMA).

Cationic polymerization of the soybean oil withdivinylbenzene comonomer initiated by boron tri-fluoride diethyl etherate results in polymers rangingfrom soft rubbers to hard thermosets, depending onthe oil and the stoichiometry employed [10]. It wasfound that the initiator was immiscible with theseoils, but that miscibility was vastly improved whenthe initiator was modified with a norway fish oilethyl ester. The copolymerization of soybean oilwith styrene and norbornadiene or dicyclopenta-diene initiated by boron trifluoride diethyl etherateresulted in polymers with good mechanical proper-ties and thermal stability.

It has been observed that the copolymerization ofsoybean oils with other comonomers results in anetwork, with a gelation time dependent on the

stoichiometry and type of the triglyceride oil used[11]. The gelation time and yield for variouscopolymers prepared from varying concentrationsof the oils, comonomers and modified initiators isreported in Table 3. The yield of the cross-linkedproduct depends on the concentration of the cross-linking agents, such as divinylbenzene, dicyclopen-tadiene, etc. As usual, cross-linking increases theglass transition temperature of the polymer. Poly-mers from different soybean oils show differentproperties, and the cross-linking density of the bulkpolymers considerably affected their thermophysicalproperties [12]. Several copolymers obtained fromcopolymerization of a soybean oil with divinylben-zene were characterized by DMA, TGA and soxhletextraction, with the results shown in Tables 4 and 5.From these results, it was clear that the compositionof the copolymer dictated the properties. Forexample, the oily component of the copolymer

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Table 4

The DMA, TGA, and Soxhlet extraction results for the samples prepared by copolymerization of soybean oil and divinylbenzene in the

presence of modified initiator

Polymer samplea Eroom(Pa)� 108 ne(mol/m3) � 103 Tg(1C) Structure (wt%) TGA (1C)

a1 a2 Cross-linked Free oil Inc. oilb T10 T50

SOY60-DVB35-BFE5 4.0 7.60 27 — 69 31 29 415 490

SOY50-DVB35-(NFO10-BFE5) 5.0 11.6 70 10 77 23 37 425 491

SOY55-DVB30-(NFO10-BFE5) 2.5 6.51 15 5 75 25 40 380 475

SOY60-DVB25-(NFO10-BFE5) 1.7 4.18 20 0 73 27 43 360 470

LSS60-DVB35-BFE5 6.0 10.4 37 - 82 18 42 423 485

LSS50-DVB35-(NFO10-BFE5) 7.0 13.0 70 0 84 16 44 425 486

LSS55-DVB30-(NFO10-BFE5) 3.8 8.35 30 8 80 20 45 405 486

LSS60-DVB25-(NFO10-BFE5) 1.9 4.18 17 0 77 23 47 395 485

CLS50-DVB35-(NFO10-BFE5) 12 18.9 90 - 88 22 48 440 485

CLS55-DVB30-(NFO10-BFE5) 10 11.4 80 - 86 14 51 436 486

CLS60-DVB25-(NFO10-BFE5) 7.8 7.21 68 - 86 14 56 433 483

Reproduced with the permission from Polymer 2001; 42: 1573 r Elsevier Science Ltd., [10].

Eroom ¼ Young’s modulus at room temperature.

ne ¼ Cross-linking density.aHere SOY represents regular soybean oil, LSS—Low saturated soybean oil, CLS—conjugated low saturated soybean Oil, DVB—

divinylbenzene, NFO—Norway Pronova fish oil ethyl ester and BFE —boron trifluoride diethyl etherate. The numerals, such as SOY60

represents 60wt% of soybean oil.bWt% of oil incorporated into the cross-linked network.

Table 3

The results from copolymerization of different soybean oils using different modified initiator system with styrene and divinylbenzene,

norbornadiene or dicyclopentadiene

Original composition (wt%) Gelation time (s) Yield (%) of cross linked

polymer after extractionTriglyceride oil Comonomers Initiators

45% LSS 32%ST+15%DVB 5%SG-I+3%BFE 3.0� 102 83

45% LSS 32%ST+15%DVB 5%SG-II+3%BFE 3.0� 102 82

45% LSS 32%ST+15%DVB 5%SG-III+3%BFE 3.0� 102 83

45% LSS 32%ST+15%DVB 5%NFO+3%BFE 3.0� 102 84

45% SOY 32%ST+15%DVB 5%NFO+3%BFE 2.4� 102 80

45% LSS 32%ST+15%DVB 5%NFO+3%BFE 3.0� 102 84

45% CLS 32%ST+15%DVB 5%NFO+3%BFE 6.6� 102 92

45% CLS 32%ST+15%DVB 5%NFO+3%BFE 6.6� 102 92

45% CLS 32%ST+15%NBD 5%NFO+3%BFE 3.5� 103 89

45% CLS 32%ST+15%DCP 5%NFO+3%BFE 2.1� 105 80

Reproduced with the permission from J Appl Polym Sci 2001; 80: 662 r John Wiley and Sons, Inc. [11].

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008988

induces reduction in the glass transition tempera-ture, stiffness and modulus.

The variation of the storage modulus (E0) and lossfactor (tan d) with temperature is shown in Figs. 4and 5, respectively, for several copolymers preparedfrom regular soybean oil. In Fig. 4, E0 is minimumfor regular soybean oil and maximum for conju-gated low saturated soybean oil. In Fig. 5, thepolymers from these oils exhibited a single loss peak

at temperatures dependent on the oil, e.g., 68 1C forregular soybean oil, 61 1C for low saturated soybeanoil and 76 1C for conjugated low saturated soybeanoil. This single loss peak indicates that the polymershad a homogeneous phase. From these results, it isclear that in all soybean oils used, the conjugatedlow saturated soybean oil gave the highest cross-linking density, glass transition and storage moduli.Copolymers were also prepared from soybean oil

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Table 5

The tensile test results for various soybean oils

Polymer sample Tg (1C) ne (mol/m3)� 102 E (mpa) sb (mpa) eb (%) Toughness (mpa)

SOY45st32-DVB15-(NFO5-BFE3) 68 1.8 71 4.1 57.1 1.67

LSS45st32-DVB15-(NFO5-BFE3) 61 5.3 90 6.0 64.1 2.86

CLS45st32-DVB15-(NFO5-BFE3) 76 22 225 11.5 40.5 4.00

Reproduced with the permission from J Polym Sci: Part B: Polym Phys 2000; 39: 62 r John Wiley and Sons, Inc. [13].

Tg ¼ Glass transition temperature.

ne ¼ Cross-linking density.

E ¼ Young’s modulus.

sb ¼ Ultimate tensile strength.

eb ¼ Elongation at break.

SOY45-ST32-DVB15-(NFO5-BFE3)LSS45-ST32-DVB15-(NFO5-BFE3)CLS45-ST32-DVB15-(NFO5-BFE3)

Temperature (°C)

1. E+10

1. E+09

1. E+08

1. E+07

1. E+06

1. E+05

Stor

age

Mod

ulus

(P

a)

-35 -15 5 25 45 85 105 12565

Fig. 4. The temperature dependence of the storage modulus (E0)

on the copolymers prepared from regular soybean oil (SOY),

Lowsat soy oil (LSS) and conjugated Lowsat soy oil (CLS) with

styrene (ST) and divinylbenzene (DVB), using Norway fish oil

modified initiator. Reprinted with permission from J Polym

Sci: Part B: Polym Phys 2000; 38: 2726 r John Wiley and Sons,

Inc. [12].

-35 -15 5 25 45 85 105 125

Temperature

Tan

δ

SOY45-ST32-DVB15-(NFO5-BFE3)

0

0.5

1

1.5

CLS45-ST32-DVB15-(NFO5-BFE3)LLS45-ST32-DVB15-(NFO5-BFE3)

65

Fig. 5. The temperature dependence of the loss modulus (tan d)for the copolymers prepared from regular soybean oil (SOY),

Lowsat soy oil (LSS) and conjugated Lowsat soy oil (CLS) with

styrene (ST) and divinylbenzene (DVB), using Norway fish oil

modified initiator. Reprinted with permission from J Polym

Sci: Part B: Polym Phys 2000; 38: 2727 r John Wiley and Sons,

Inc. [12].

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008 989

and divinylbenzene, using boron trifluoride diethyletherate, resulting in heterogeneous polymericmaterials [10].

The tensile properties of several soybean oilpolymers ranging from elastomers to hard, ductileand relatively brittle polymers are shown in Fig. 6[13]. Generally, it is observed that the ultimatetensile strength increases and the elongation atbreak decreases with an increase in the degree ofcross-linking. At lower strain (o10%), the increasein stress is rapid, while at higher strain (410%), theregular and low saturated soybean oil polymersexhibit a slow increase in the stress. The conjugated

low saturated soybean oil polymers show a yieldpoint.

The tensile fracture surface of polymer samples(with 35 weight % conjugated low saturatedsoybean oil) was observed under a scanning electronmicroscope and shown to be very similar to those ofepoxies [Fig. 7]. The SEM micrograph of thefracture surface and the mist region of the fracturedsurface are shown in Figs. 7(a) and 7(b), respec-tively, for one sample.

The results for damping properties of severalsoybean oils over a broad range of temperature andfrequency are reported in Table 6 [14]. The high

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0 20 40 60 80

Strain (%)

0

4

8

12

Stre

ss (

MP

a)

SOY45-ST32-DVB15-(NFO5-BFE3)

CLS45-ST32-DVB15-(NFO5-BFE3)LLS45-ST32-DVB15-(NFO5-BFE3)

Fig. 6. The tensile stress-strain curves from three soybean oil

polymers i.e. regular (SOY), low saturated (LSS) and conjugated

low saturated (CLS) soybean oil polymers for same percentage of

oil and comonomers styrene (ST) and divinylbenzene (DVB).

Reprinted with permission from J Polym Sci: Part B: Polym Phys

2000; 39: 63 r John Wiley and Sons, Inc. [13].

Fig. 7. The SEM micrograph of sample CLS35ST39-DVB18-

(NFO5-BFE3) highlighting the mechanically fractured surface of

the sample and the mist region of the mechanically fractured

surface. Reprinted with permission from J Polym Sci: Part B:

Polym Phys 2000; 39: 75 r John Wiley and Sons, Inc. [13].

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008990

damping intensities are ascribed to the contributionfrom the large number of ester groups directlyattached to the soybean oil–styrene–divinylbenzenecopolymer chains. The variation in the glasstransition temperature with cross-linking density isshown in Fig. 8 for several soybean oil polymers.The three soybean oil polymers showed the sameglass transition temperature, but differ in the valueof the loss tangent maxima. The broad dampingregions were attributed to segmental inhomogeneityinduced on cross-linking. However, cross-linkingalso reduced the damping intensities by restrictingthe polymer segmental motions of the homogeneouspolymeric materials. Thus, it is expected thatefficient damping materials (for sound and vibra-tional applications) would result on the chemicalor physical combination of two or more struct-urally dissimilar soybean oil-based polymersto form interpenetrating networks (IPN) with aphase separated morphology. In such a case,broad damping regions would be facilitated byphase microheterogeneity resulting from the forma-tion of IPNs, rather than by the segmentalinhomogeneity [14].

Some soybean oil polymers prepared by cationiccopolymerization show a good shape-memory effect[15]. Shape-memory refers to the ability of some

materials to remember a specific shape on demand,even after very severe deformation. Such materialshave applications in civil construction, mechanicsand manufacturing, electronics and communica-tions, printing and packaging, medical equipment,recreation and sports, and household items.A shape-memory polymer exhibits mechanicalbehavior that includes fixing the deformation ofthe plastics at room temperature and recovering thedeformation as elastomers at relatively high tem-peratures [16–19]. Shape-memory polymers basi-cally consist of two phases: a reversible phase and afixed phase. The reversible phase refers to thepolymer matrix, which has a glass transitiontemperature (Tg) or a melting temperature (Tm)well above the application temperature. The fixedphase is composed of either chemical or physicalcross-links that are relatively stable at a temperaturehigher than the Tg or Tm of the reversible phase.At a temperature above Tg or Tm, the shape-memory polymer achieves a rubbery elastic state in

ARTICLE IN PRESS

υe (mol/m3)

10 100 1000 10000 100000

0

20

40

60

80

100

Tg

(°°C

)

120

SOY45-(ST+DVB) 47-(NFO5-BFE3)LSS45-(ST+DVB) 47-(NFO5-BFE3)CLS45-(ST+DVB) 47-(NFO5-BFE3)

Fig. 8. The dependence of the glass transition temperature (Tg)

on cross-linking density (ne) for different soybean oil polymers.

Reprinted with permission from Polym Adv Technol 2002; 13:

444 r John Wiley and Sons, Ltd. [14].

Table 6

Results for the damping properties of the copolymers prepared from different soybean oils

Polymer sample Tg(1C) ne(mol/m3) (tan d)max (tan d)rt DT at tan d40.3 (1C) TA (K) Half-width (1C)

SOY35st39-DVB18-(NFO5-BFE3) 79 4.7� 102 0.88 0.12 52–115 (63) 37.5 47

SOY45st32-DVB15-(NFO5-BFE3) 68 1.8� 102 0.85 0.32 23–113 (90) 48.4 61

SOY55st25-DVB12-(NFO5-BFE3) 30 1.0� 102 0.84 0.83 �2–65 (67) 36.3 51

LSS35st39-DVB18-(NFO5-BFE3) 80 7.3� 102 0.86 0.11 23–113 (90) 48.4 51

LSS45st32-DVB15-(NFO5-BFE3) 61 5.3� 102 0.89 0.37 19–97 (78) 46.2 52

LSS55st25-DVB12-(NFO5-BFE3) 32 3.9� 102 1.00 0.96 �6–83 (89) 50.1 57

CLS35st39-DVB18-(NFO5-BFE3) 82 3.4� 103 0.94 0.07 58–116 (58) 41.8 42

CLS45st32-DVB15-(NFO5-BFE3) 76 2.2� 103 0.79 0.18 48–120 (72) 43.1 53

CLS55st25-DVB12-(NFO5-BFE3) 38 6.5� 102 1.08 0.80 10–77 (67) 52.9 44

Reproduced with permission from Polymers for Advanced Technologies 2002; 13: 439,441 r John Wiley and Sons, Ltd., [14].

Tg ¼ Glass transition temperature.

ne ¼ Cross-linking density.

(tan d)max ¼ Loss tangent maxima.

(tan d)rt ¼ Loss tangent at room temperature.

TA ¼ tan d area.

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008 991

which it can be easily deformed by an external force.When the polymer is cooled to room temperature,the deformation is fixed due to the frozen microBrownian motion of the reversible phase. Thehardened reversible phase effectively resists elasticrecovery resulting from the tendency of the orderedchains to return to a more random state, but thedeformed shape readily returns to its original shapeupon heating above Tg or Tm. The driving force forthe shape recovery is primarily entropy, especially

the strong relaxations of the oriented polymerchains between the cross-links.

Table 7 shows the shape-memory properties ofseveral soybean oil polymers. It is observed that thetype of soybean oil greatly affects the shape-memory properties of these polymers (e.g., seeNo. 1–3). The polymers from reactive soybean oilshow higher degree of fixed deformation (FD value)and a lower deformability at a temperature higherthan Tg (D value). All of the polymeric materialsshow 100% recovery (R) of fixed deformation uponreheating to Tg plus 50 1C.

The time for gelation and vitrification of varioussoybean oil polymer systems has been investigatedover a range of isothermal curing temperatures [20].All the fully cured thermosets were first made atroom temperature and then subjected to post-curingat elevated temperatures. The thermal stability anddynamic mechanical behavior of the resultingthermosets were not particularly sensitive to thecuring conditions. However, varying the curing timeat low and high temperatures did affect thestructural characteristics of the polymer backbone,affecting the shape-memory and tensile mechanicalproperties. The isothermal time–temperature–trans-formation (TTT) cure diagram, developed to studythe epoxy systems [21–23], is a very useful tool forinvestigating the cure process of the soybean oilsystems. The cure temperatures between Tg,gel, (Tg

at which the system gels and vitrifies simulta-neously) and TgN (maximum Tg of fully curedsystem), where gelation precedes vitrification, are ofpractical importance. It was observed that gelation

ARTICLE IN PRESS

Fig. 9. The 1H NMR spectra of acrylated epoxidized soybean oil (AESO). Reprinted with the permission from J Appl Polym Sci 2001;

82: 710 r John Wiley and Sons, Inc. [1].

Table 7

Shape memory properties of soybean oil polymers

Polymer sample Tg (1C) ne (mol/m3) Shape memory results (%)

D FD R

SOY45ST32-DVB15-(NFO5-BFE3) 68 1.8� 102 100 80 100

LSS45ST32-DVB15-(NFO5-BFE3) 61 5.3� 102 86 96 100

CLS45ST32-DVB15-(NFO5-BFE3) 76 2.2� 103 77 98 100

SOY45ST32-(DVB5-NBD5-DCP5)-(NFO5-BFE3) 42 9.8� 10 100 63 100

(SOY22.5-LSS22.5)-ST32-(DVB5-NBD5-DCP5)-(NFO5-BFE3) 43 1.3� 102 100 74 100

(SOY15-LSS15-CLS15)-ST32-(DVB5-NBD5-DCP5)-(NFO5-BFE3) 44 2.7� 102 100 75 100

SOY45ST20-(DVB9-NBD9-DCP9)-(NFO5-BFE3) 68 3.1� 102 100 97 100

(SOY22.5-LSS22.5)-ST20-(DVB9-NBD9-DCP9)-(NFO5-BFE3) 70 3.7� 102 100 98 100

(SOY15-LSS15-CLS15)-ST20-(DVB9-NBD9-DCP9)-(NFO5-BFE3) 74 5.2� 102 100 99 100

Reproduced with permission from Journal of Applied Polymer Science 2002; 84: 1539 r John Wiley and Sons, Ltd., [15].

Tg ¼ Glass transition temperature.

ne ¼ Cross-linking density.

D ¼ Deformability of the material at temperature higher than Tg.

FD ¼ Degree to which the deformation is fixed at ambient temperature.

R ¼ Final shape recovery.

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008992

occurs at approximately 15% conversion of thereactants, and the yield of cross-linked polymerscontinued to increase following gelation. However,only about 50% of the soybean oil reactants wereconverted into cross-linked polymers when thesystem vitrified. Thus, in order to obtain fully curednetworks, the materials were subsequently post-cured at elevated temperatures.

2.1.2. Modified soybean oil polymers

Several types of functionalization can be obtainedat various active sites within the triglyceridestructure, such as the double bond, the ester group,the allylic carbons, and the carbons a to the ester

group. Various chemical pathways for functionali-zation of these triglycerides have been studied.LaScala and Wool et al. [1] analyzed optimizationof the effect of chemical functionalization on themechanical properties and thermal stability of someresins. The viscoelastic properties of resin samplesmade of AESO and cured at room temperature withvarying amounts of styrene were studied. The 1HNMR spectra of AESO are shown in Fig. 9. Sometriglyceride-based monomers prepared from acrylicacid are shown in Fig. 10. It was found that both E0

and Tg increased with increasing styrene content inthe copolymers. The styrene content at 33.3wt%, ora 2:1 AESO to styrene ratio, was considered optimal

ARTICLE IN PRESS

O

O

O

O

O

OO

O

OH

O

O

OH

O

O

OH

O

O

OH

O

O

O

O

O

O

C

OOH

O OH

O

O

O

O

O

O

OH OH

OH

O O

O

HO

O O

O

OH

OO

O

OH

OH

O O

O

OH

Acrylated Epoxidized Soybean Oil (AESO)

Maleinated Soybean Oil Monoglyceride (SOMG/MA)

Maleinated Hydroxylated Soybean Oil (HSO/MA)

Fig. 10. Different triglyceride-based acrylic monomers. Reprinted with the permission from J Appl Polym Sci 2001; 82: 706r John Wiley

and Sons, Inc. [1].

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008 993

with respect to the properties. The variations ofdamping peak (tan d) of AESO–styrene copolymerwith temperature are shown in Fig. 11. The differentcompositions of the AESO–styrene copolymerswere used to study the dynamic mechanicalbehavior of the copolymers. The copolymer with50% AESO showed a very sharp loss tangent peak,which broadened with the increasing contents ofAESO.

Baki Hazer and co-workers [24] reported that thesoybean fatty acid and poly(hydroxy alkanoate)(PHA) reacted under UV irradiation to form across-linked biopolyester. It is believed that in the

prevailing conditions, the esterification reactionproceeds along with cross-linking via a free radicalmechanism. A bacterial polyester containing olefinicgroups in the side chains was prepared by feedingpseudomonas oleovorans with soybean fatty acids.The structure of PHA with unsaturated side chainssoybean fatty acids is shown in Fig. 12. After cross-linking, the biopolyester became a smooth and lesssticky elastomeric film. The cross-linked biopoly-ester, obtained thermally at 60 1C with benzoylperoxide initiation, exhibited the highest cross-linking density. The cross-linking was determinedby sol–gel analysis. The swelling properties of these

ARTICLE IN PRESSV. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008994

biopolyesters were studied and the number averagemolecular weights were also calculated using theFlory-Rehner equation [25]. The cross-link densitycan be increased by irradiation with shorterwavelength. It was also reported that while poly-merization of the soybean oil is difficult, thebiopolyester from soybean oil fatty acids is morereactive than the relative oil for polymerization.

2.2. Fish oil polymers

Fish oil is biodegradable and is readily availableas a byproduct in the production of fishmeal. Fishoils have a triglyceride structure with a highpercentage of polyunsaturated omega 3 fatty acidside chains, which can contain as many as 5–6 non-conjugated carbon–carbon double bonds per ester

100% AESO0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1-150 -100 -50 0 50 100 150 200

80% AESO60% AESO50% AESO

Temperature (°C)

Tan

δ

Fig. 11. Plot of dynamic mechanical properties of AESO–styrene

copolymers against temperature using different compositions

(AESO 50–100%) of the copolymers. Reprinted with the

permission from J Appl Polym Sci 2001; 82: 714 r John Wiley

and Sons, Inc. [1].

O CH CH2

C

O

O CH

CH2

CH3

CH2

CH

HC

CH2

HC

CH

CH3

x

Z

PHA-Soybean

Fig. 12. The structure of poly(hydroxy alkanoate) (PHA) containing un

the permission from Polymer Bulletin 2001; 46: 391 r Springer-Verlag

side chain [26]. Fish oils find use in industry in theproduction of protective coatings, lubricants, sea-lants, inks, animal feed and surfactants [27].Regular and conjugated fish oils prove to becationically polymerizable monomers [26]. Polymersfrom fish oil have been prepared with divinylben-zene, dicyclopentadiene and norbornadiene como-nomers [26]. The polymers obtained from fish oilwere found to be typical thermosetting materials[26]. Three distinct decomposition states were foundby TGA, corresponding to the evaporation ofunsaturated free oil present in the bulk polymer,carbonization of the cross-linked polymer andsubsequent oxidation of the carbons [26].

Both regular oil and conjugated fish oils can beused to produce hard and stiff polymers havingmoduli comparable to those of the conventionalplastics [28]. In Fig. 13, fish oil polymers arecompared with commercially available polymers.The glass transition temperature of the conjugatedfish oil (CFO) polymer is nearly 110 1C, which ishigher than Tg for polystyrene. The thermosettingnature of the fish oil polymers results in animprovement in thermal stability at higher tempera-tures (T4200 1C) as compared to the thermoplasticpolymers. The conjugated fish oil resulted inpolymeric materials with better thermal stabilityand mechanical properties as compared to theregular fish oil polymers. However, regular fish oilpolymers were observed to have relatively goodcreep resistance properties [28]. These polymerswere found to have high cross-linking densities. Thebulk polymer was mainly composed of insolublesubstances (65–80wt%). The homopolymerizationof regular fish oil ethyl ester initiated by borontrifluoride diethyl etherate (BFE) resulted in a

CH2

C

Oy

Saturated units:x = 2 for hexanoate.x = 4 for octanoate.x = 6 for decanoate.

Unsaturated units:y = 0 for -ene.y = 1 for -diene.y = 2 for -triene.z = 1-3.

saturated side chains of fatty acids, PHA–soybean. Reprinted with

, Inc. [24].

ARTICLE IN PRESS

Temperature (°°C)

Stor

age

Mod

ulus

(P

a)

Tan

δ

1e+10

1e+9

1e+8

1e+7

1e+6

50

CFO-DVB-38

Polystyrene

Polyethylene

Polystyrene

CFO-DVB-38

Epoxy

Polyethylene

Epoxy

100 150 200 250

0.0

0.2

0.4

0.6

0.8

1.0

Fig. 13. The comparison of the storage modulus (E0) and loss

factor (tan d) for conjugated fish oil (CFO-DVB-38) and some

commercially available polymers. Reprinted with the permission

from Polymer 2000; 41: 7935 r Elsevier Science Ltd., [25].

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008 995

viscous oil and they did not gel at all at roomtemperature or above. However, conjugated fish oilis more reactive than regular fish oil and the simplehomopolymerization of conjugated fish oil results ina soft and solid material. The addition of alkenecomonomers, such as divinylbenzene, norborna-diene, dicyclopentadiene, etc., facilitated gelation ofregular fish oil ester system. The gel time varies from1min to a few hours at room temperature depend-ing upon the oil and comonomer contents. Regularand conjugated fish oil ethyl ester form polymerswith divinylbenzene in the presence of BFE.Regular fish oil resulted in soft to hard thermosetsdepending upon the amount of divinylbenzene,whereas conjugated fish oil resulted in very hardthermosets.

Many other alkene comonomers, such as furfural,benzoquinone, p-mentha-1, 8-diene, furan, vinylacetate, etc., were also examined in BFE-initiatedcopolymerizations [29]. Copolymerization of thesealkene comonomers with fish oil or conjugated fishoil generated soft to hard polymers in the presenceof divinylbenzene, norbornadiene or dicyclopenta-diene comonomers. A wide range of alkene como-nomers resulted in viable solid plastic materials, butneither copolymerizing fish oil nor conjugated fishoil could be copolymerized with p-mentha-1, 8-diene, methyl methacrylate, isoprene, methyl croto-nate, phenol, linalool, furfural, bisphenol A, etc.Among various Lewis acids, boron trifluoride

diethyl etherate proved to be the most effectiveinitiator for copolymerization.

A number of fish oils have also been polymerizedwith styrene and divinylbenzene cationically in thepresence of boron trifluoride diethyl etherate asinitiator [30]. In addition to the good thermalstability, and physical and mechanical properties,the polymeric products also showed even morepromising and valuable properties, such as gooddamping and shape-memory properties. The tensilefractured surfaces of the fish oil polymers have beenstudied to obtain SEM micrographs of the fracturedsurfaces of fish oil polymers such as those shown inFig. 14. It is observed that Norway fish oil (NFO)polymers have smooth surfaces even at highermagnifications, whereas triglyceride fish oil (TFO)polymer results in rough surfaces.

2.3. Corn oil polymers

Corn oil is one of the cheapest commerciallyavailable vegetable oils and finds use in food andlivestock feed as well as in the production ofethanol, which is utilized as a fuel. It has atriglyceride structure, with approximately 4.1 car-bon–carbon double bonds per molecule in fatty acidside chains [31]. The fairly high degree of unsatura-tion present in corn oil makes it possible tocopolymerize this oil with other monomers. Other-wise, corn and soybean oils have similar chemicalstructures, with three fatty acid chains composed ofoleic acid, linoleic acid and linolenic acid [32].

Polymers have been prepared by cationic poly-merization of corn oil, styrene and divinylbenzene inthe presence of boron trifluoride diethyl etherate[31]. Corn oil and conjugated corn oil wereeffectively copolymerized with comonomers. Thecopolymers obtained with conjugated corn oilshowed better mechanical properties and thermalstability than the corresponding simple corn oilpolymers. The polymers possess a wide variety ofmechanical properties, such as tensile, flexural andcompressive strengths, ranging from elastomers totough and rigid plastics. The dynamic mechanicalproperties of several corn oil polymers are shown inFig. 15.

Fig. 16 shows the dependence of the weightpercent of cross-linked polymers on the cure timeand the corn oil contents in the copolymers.Fig. 16(a) shows that the conjugated corn oilresulted in polymers with higher cross-linked con-tents in comparison to the polymers from regular

ARTICLE IN PRESS

Fig. 14. The SEM micrograph of the mechanically fractured surfaces of samples NFO49ST33-DVB15-BFE3, CFO49ST33-DVB15-BFE3

and TFO49ST33-DVB15-BFE3. Reprinted with the permission from Polymer 2001; 42: 10144 r Elsevier Science Ltd. [29].

1.0E+10

1.0E+9

Stor

age

Mod

ulus

(P

a)

COR35-ST39-DVB18-(NFO5-BFE3)

1.0E+8

1.0E+7

1.0E+6

1.0E+5

0.6

0.4

0.2

0-50 0 50 100 150 200

COR45-ST32-DVB15-(NFO5-BFE3)COR55-ST25-DVB12-(NFO5-BFE3)

Temperature (°C)

Los

s F

acto

r (t

an δ

)

Fig. 15. The temperature dependence of the storage modulus (E0)

and loss factor (tan d) for corn oil polymers prepared from

different concentrations of corn oil, keeping the styrene and

divinylbenzene contents in same ratio (3:2). Reprinted with the

permission from J Appl Polym Sci 2003; 90: 1833 r Wiley

Periodicals, Inc. [30].

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008996

corn oil. Fig. 16(b) indicates that the systemunderwent a slow increase in the yield of cross-linked polymer after gelation. It is also observedthat with the same curing time, only a 5 1C increasein the cure temperature made an appreciabledifference in the yields of cross-linked polymers(shown in Fig. 16(b)). A plot of the shape recoveryproperties of the conjugated and regular corn oilcopolymers at different temperatures is reported inFig. 17. It is observed that 50% shape recovery ofdeformations was reached at 42 and 44 1C forconjugated and regular corn oil polymers, respec-tively, and attained complete recovery for conju-gated corn oil polymer at 75 1C and 96% recoveryfor regular corn oil polymer at the same tempera-ture. Regular corn oil copolymer is found to possesssuperior damping characteristics when compared toconjugated corn oil copolymer. This is attributed tothe high reactivity of conjugated oil, leading todensely cross-linked polymers.

2.4. Tung oil polymers

Tung oil is one of the oldest known drying oilsand finds numerous applications in the paintindustry. It is extracted from the seeds of the tung

ARTICLE IN PRESS

35°C

40°C

0 100 200

Cure Time (min)

Wt

% o

f cr

oss-

linke

d po

lym

er

0

20

40

60

80

100

(a)

COR-ST-DVB CCOR-ST-DVB

0 20 40 60 80 100

Corn Oil Contents (%)

0

20

40

60

80

100

(b)

400300

Fig. 16. (a) show the dependence of the weight percent of the cross-linked polymer obtained from COR45ST32-DVB15-(NFO5-BFE3) on

cure time at 35 and 45 1C and; (b) the weight percentage of cross-linked polymers prepared from conjugated and simple corn oil versus

corn oil contents. Reprinted with the permission from J Appl Polym Sci 2003; 90: 1833 r Wiley Periodicals, Inc. [30].

Rec

over

y (%

)

Temperature (°°C)

COR45-ST32-DVB15-(NFO5-BFE3) CCOR45-ST32-DVB15-(NFO5-BFE3)

100

80

60

40

20

0

20 40 60 80 100

Fig. 17. The study of the shape-recovery results for the polymer

from conjugated and regular corn oil for sample with composi-

tion OIL45ST32-DVB15-(NFO5-BFE3) at different tempera-

tures. Reprinted with the permission from J Appl Polym Sci 2003;

90: 1836 r Wiley Periodicals, Inc. [30].

Fig. 18. The structure of a-elaeostearic acid. Reprinted with the

permission from Biomacromolecules 2003; 4: 1018 r American

Chemical Society [34].

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008 997

tree, with its main constituent a glyceride ofelaeostearic acid with a conjugated triene structure(Fig. 18). This highly unsaturated, conjugatedsystem is largely responsible for the rapid polymer-ization and outstanding drying properties of the oil[33]. Tung oil has been polymerized by both freeradical and cationic polymerizations. Larock andcoworkers [34,35] studied the cationic and thermalpolymerization of tung oil in detail. Tung oil iscationically copolymerized with divinylbenzene inthe presence of boron trifluoride diethyl etherate,resulting in hard plastics [34]. The cationic copoly-merization of tung oil is found to be very reactive. Itwas observed that tung oil is very sensitive to thecationic initiator boron trifluoride diethyl etherate,

and forms an irregular polymeric solid within a fewseconds after the addition of this initiator at roomtemperature. The gel time ranged from a fewseconds to 1min depending, on the oil and othermonomer compositions. The addition of a lessreactive oil, such as soybean oil, increases the geltime from second to minutes or hours, againdepending upon the oil and other monomercompositions. The level of conversion of the startingmaterial into a cross-linked product depends on thecomposition of the material. Tung oil polymerspossess very good dynamic mechanical properties aswell as thermal stability at room temperature. Theseare thermally stable upto 200 1C and 10% weightloss was recorded at around 400 1C.

Tung oil can also be copolymerized with styreneand divinylbenzene by thermal polymerization [35].The 1H NMR spectra of the tung oil, styrene,divinylbenzene and extracted soluble contents fromthe sample with 50% tung oil is reported in Fig. 19[35]. These results are used to calculate the oilcontent in a particular sample. The thermal poly-merization of tung oil was reported to involveprimarily the dimerization of the elaeostearic acid,producing monocyclic dimeric fatty acid groups at

ARTICLE IN PRESS

Fig. 19. The 1H NMR spectra of (a) tung oil (TUN), (b) styrene

(ST), (c) divinylbenzene (DVB) and (d) the extracted soluble

substances from the sample TUN50ST20-DVB30 bulk polymer.

Reprinted with the permission from Biomacromolecules 2003; 4:

1021 r American Chemical Society [34].

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008998

200 1C or above [36–37]. When polymerized at hightemperatures (in a range of 200–300 1C), the resultingproducts ranged from viscous oils to weak rubberyfilms. Aromatic comonomers have been introducedto produce viable polymeric materials. A widevariety of viable transparent polymeric materials

ranging from elastomers to tough and rigid plasticshave been prepared from thermal copolymerizationof the tung oil, styrene and divinylbenzene [35]. Thestoichiometry and the addition of catalysts greatlyaffected the thermophysical and mechanical proper-ties of the polymers. The addition of metalliccatalysts proved to be a very effective means toaccelerate the thermal copolymerization leading tohigh cross-link densities and improved properties ofthe bulk polymers. However, varying the oxygenuptake and the addition of various peroxides had noeffect on the resulting polymers.

Trumbo and Mote [38] reported the synthesis ofcopolymers from tung oil and diacrylate by Diels-Alder reaction and studied the properties of thefilms produced from these copolymers using 1,6-hexanediol diacrylate and 1,4-butanediol diacrylate.The copolymers produced were completely soluble.The molecular weight distributions of the copoly-mers were broad and multimodal. The films of thecopolymers were readily prepared and when cured,exhibited good solvent resistance, high hardness andgood gloss.

2.5. Linseed oil polymers

2.5.1. Natural linseed oil polymers

Linseed oil, obtained from the linseed seed, is afatty acid ester triglyceride and is composed of about53% linolenic acid, 18% oleic acid, 15% linoleic acid,6% palmitic acid and 6% stearic acid [39]. It istraditionally used as a drying oil for surface-coatingapplications. To make it a superior drying oil interms of film properties, different olefinic monomers,such as styrene have been copolymerized with linseedoil [40–42]. Linseed oil is polymerized by cationic,thermal, free radical polymerization, as well as byoxidative polymerization [43]. The process of auto-oxidative curing of linseed oil with initiation,propagation and termination steps is shown inScheme 3. It is observed that in the initiation step,naturally occurring hydroperoxides decompose toform free radicals. This step can be catalyzed eitherby the inclusion of driers (pigments used as catalysts)or the application of heat. These free radicals reactwith antioxidants and after consuming the antiox-idants, react with the fatty acid chains of the dryingoil. The propagation then proceeds by the abstrac-tion of the hydrogen atoms present between doublebonds of the methylene groups, which result in thefree radical 1. Radical 1 is resonance stabilized, andcan react with oxygen to form radical 2, as shown inScheme 3. The peroxy free radical may be conjugatedor non-conjugated. This can regenerate free radical 1by abstracting hydrogen from methylene groups.After this termination, cross-linking proceeds.The termination results in the formation of structures3, 4 and 5. Cobalt, lead and zirconium-2-ethylhex-anoates are generally used as catalysts for oxidativepolymerization of linseed oil. It is found thatcobalt-2-ethylhexanoate was active during the oxida-tive step and lead and zirconium catalysts actedduring the polymerization step. Cobalt–zirconiumcomplex gave the best results, and under specifiedconditions, zirconium catalyst was more efficientthan lead.

Soucek et al. [44] used DSC to study the auto-oxidative curing of linseed oil, catalyzed by variousmetal catalysts. A manganese drier was used tocatalyze the reaction at the coating surface (topdrier) and a zirconium drier was used to catalyze thereaction throughout the entire film thickness(through drier). It is a common practice to use acombination of top and through driers. Fig. 20shows the DSC scans for linseed oil using differentdrier systems at 130 1C.

ARTICLE IN PRESS

Scheme 3. The autoxidation process for the curing of linseed oil showing initiation, propagation and termination steps of the reaction.

Reprinted with the permission from Prog Org Coat 1998; 33: 220 r Elsevier Science S. A. [42].

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008 999

Linseed oil has been styrenated for use inpolymerizations to obtain some desired film proper-ties [45]. There are two methods of styrenation ofoils, dependent on the mode of generation of freeradicals: the classical method and the macromermethod. In the classical method, free radicals areformed by thermolysis, either in the absence (forconjugated oils) or in the presence (for non-conjugated oils) of an initiator, such as benzoylper-oxide. The degree of conjugation and unsaturationhas a crucial effect on the formation of free radicalson the oil molecules. The process of styrenation oflinseed oil proceeds through different stages, de-

picted in Scheme 4, showing the process ofstyrenation of linseed oil and castor oil. The oilsare first interesterified and then the macromer isprepared from the reaction of interesterified productand acrylic acid. Finally, the macromers are reactedwith styrene. The macromonomers of linseed oilwere prepared by transesterification of methyl-methacrylate (MMA) with partial glycerides [46].Styrenation was achieved via a free radical mechan-ism using benzoylperoxide as the initiator. Scheme 5shows the detailed mechanism for the preparationof partial glycerides and their styrenation. In themacromer method, the macromer was obtained

ARTICLE IN PRESS

O

O

O

O

O

O

+

Interes

O

O

O

O

O

O

OH

OH

O

O

O

O

O

O

+

++

OH

O

O

OH

OH

OH

O

O

OHO

Acrylic Acid (CH2=CH-COOH)-H2O

O

O

O

O

O

O

O

O

OH

O

OHO

StyreneO

O

O

O

O

O

SMacromer

Interesterification Produ

Linseed Oil

Scheme 4. Styrenation of the linseed oil and castor oil through intere

styrene to form styrenated oil. Reprinted with the permission fromMacr

0 20 40 60 80 100

Time (min)

Exotherm

LIN-Mn (0.1) @ 130°C LIN-TIA (0.5) @ 130°C LIN-TIP (0.5) @ 130°C

Fig. 20. Differential scanning calorimetric isothermal exotherms

for linseed oil cured with three different metal catalysts,

manganese drier, titanium (di-isopropoxide) bis (acetyl-aceto-

nate) (TIA) and titanium (IV) isopropoxide (TIP) at 130 1C.

Reprinted with the permission from Progress in Organic Coatings

1996; 28: 254 r Elsevier Science S. A. [43].

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–10081000

through reaction of hydroxyl-containing oil speci-mens with vinyl monomer and then this macromerwas homopolymerized or copolymerized with styr-ene [47]. Semidrying and non-conjugated oils weremixed with conjugated drying oils to producehomogeneous styrenated products [48]. When clas-sical and macromer methods were compared, it wasfound that macromer technique resulted in homo-geneous products in high yield.

The effect of cobalt-2-ethylhexanoate drier on theoxidative polymerization of linseed oil was investi-gated [49]. It was found that the cobalt catalystsaccelerated all of the oxidation reactions involved inthe process, and improved the formation of a solidfilm at the surface, but a viscous oil remained underthis surface film. The addition of cobalt drier onlyinfluenced the kinetics, but did not alter the reactionproducts.

O

O

O

O

O

O OH

OH

OH

terification

OH

+

+ Other possible isomers

O

O

O

O

O

O

O

OH

OH

O

O

O

O

OH

O

CH CH CH2

CHn

tyrenated Oil

ct (IP)

Castor Oil

sterification of oils which react with acrylic acid and finally with

omol Mater Eng 2000; 283: 17rWiley–VCH Verlag GmbH [44].

ARTICLE IN PRESS

O

O

O

O

O

O

Triglyceride OilGlycerol

OH

OH

OH+ +

O

OH

O

OO

OH

OH

O

O

Mixture of Partial Glyceride

+O

OH

O

O

O

OH

OH

O

O

H2C

CH3

CC

O CH3

O-CH3OH

+

O

O

O

OCCO

O

O

OCH

2

CH2

CH2

CH2

C

CH3CH

2

CH3

CH3

CH3

HC CHH2C

H3C

CH2

CH2

CH2

CH2

CH2

CH

CH2

CH

H3C

H3C

H3C

CH2

CH3

CO

O

CCO

O

O

O

O

OCCO

O

HCH2C

Benzoyl peroxide

O

O

O

O

CO

O

n

O

OCCO

O

CCO

O

Benzoyl peroxide

n

n

O

O

CO

O

CO

O

Styrenated Oil

Scheme 5. The process of preparation of the partial glyceride and then the styrenation of the partial glyceride through free radical

mechanism in presence of benzoylperoxide. Reprinted with the permission from J Appl Polym Sci 2003; 88: 2374–75 r Wiley Periodicals,

Inc. [45].

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008 1001

For films cured with the cobalt drier, thequantification of the oxidation product shows lowerconcentrations of carboxylic acids, ketones andalcohols [49]. The efficiency of peroxide decomposi-tion by the cobalt, zirconium and calcium/zirco-nium drier was compared by measuring thevariations of peroxide value as a function ofoxidation time. The influence of different catalystsand anhydride hardeners on the curing of polymernetworks based on epoxidized linseed oil has beenstudied [50]. Generally, tertiary amines and imida-zoles were used as catalysts. The variation of loss

factor and storage modulus with temperature forepoxidized linseed oil—cis-1,2,3,6-tetrahydrophtha-lic anhydride (ELO—THPA) system is depicted inFig. 21. A wide range of temperature from �140 to+220 1C was used for the study. On using imidazolecatalysts, the epoxidized linseed oil was cured to amaximum extent, leading to high conversion ofanhydrides (nearly double) and increased stiffness.By using tertiary amine as a catalyst, lower stiffnesswas observed in comparison to that with theimidazole catalyst. When the catalyst contentwas increased, the conversion of anhydride was

ARTICLE IN PRESSV. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–10081002

observed to be low due to the fast gelling of thesystem. On decreasing the catalyst concentration, itwas observed that the anhydride conversion ismaximum leading to good thermal stability andmechanical properties, such as flexural and Young’smoduli, Tg, etc.

2.5.2. Epoxidized linseed oil polymers

A series of epoxynorbornane-modified linseed oilswere prepared as a function of the norbornanecontent and were characterized by various methods

0.2

10

0.15

0.1

0.05

0

100

1000

10000 0.4

0.35

0.3

E’

(MP

a)

-140 - 80 20 40 100 160

0.25

1

Temperature (°C)

Tan

δ

Fig. 21. The temperature dependence of loss factor (tan d) andstorage modulus (E0) at a frequency of 1Hz for an epoxidized

linseed oil—cis-1,2,3,6-tetrahydrophthalic anhydride (ELO–

THPA) system. Reprinted with the permission from Polymer

2000; 41: 8609 r Elsevier Science Ltd., [49].

+4

7

7 7O

O

O

O

OO

7

0.76-0. 90 MPa

250 °C

O

O

O

O

OO

47

7 7

7NLO--25

NLO--50

NLO--100

[a]

Scheme 6. The reaction process of the preparation of the norbornan

Reprinted with the permission from J Polym Sci: Part A: Polym Chem

of analysis, such as FTIR, NMR, etc. [51]. Thecationic photopolymerization of epoxynorbornanelinseed oil and epoxidized linseed oil was studied byvarious methods of characterization. The prepara-tion of epoxynorbornane linseed oil and norbor-nane linseed oil is detailed in Scheme 6. The 1HNMR spectra of linseed oil, norbornane linseed oiland epoxynorbornane linseed oil are shown in Fig.22. Figs. 23 and 24 show the effect of the reactiveand non-reactive diluents on the rate of polymeriza-tion [51]. The addition of reactive or non-reactivediluents reduced the viscosity of the formulationsand was found to have significant effect on epoxyconversion and the rate of polymerization ofepoxidized norbornane linseed oil. It was reportedthat the photopolymerization of epoxides wasaccelerated due to the presence of vinyl ether[52,53]. This was attributed to the generation of alarge number of propagating cationic species via aredox reaction between the vinyl ether and thephotoinitiator diaryliodonium salt. The mechanismfor the photoinitiated cationic polymerizationof epoxynorbornane linseed oil is depicted inScheme 7.

Soucek and coworkers [54] have studied theproperties of UV-curable hybrid films derived fromepoxynorbornane linseed oil. Different levels ofepoxynorbornane linseed oil and tetraethylortho-silane (TEOS) were used in the study. The organic–

O

O

O

O

OO

7

7

7

74

H2O

2/Tungstate

60 °C

O

O

O

O

OO

O O

O

O

O

O

7

7

7

74

NLO--25

NLO--50

NLO--100

ENLO--25

ENLO--50

ENLO--100[b]

e linseed oil (NLO) and epoxynorbornane linseed oil (ENLO).

2003; 41: 3444 r Wiley Periodicals, Inc. [50].

ARTICLE IN PRESS

Fig. 22. The 1H NMR spectra of (a) linseed oil, (b) norbornane linseed oil and (c) epoxynorbornane linseed oil. Reprinted with the

permission from J Polym Sci: Part A: Polym Chem 2003; 41: 3446 r Wiley Periodicals, Inc. [50].

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008 1003

inorganic hybrid films are formed either from theinorganic phase formation within the organic filmor a simultaneous polymerization of both organicand inorganic reactive groups. It was also observedthat the incorporation of TEOS oligomers improvedthe performance of films and enhanced tensilestrength, fracture toughness, thermal stability andgeneral coating properties of epoxynorbornanelinseed oil.

Turri et al. [55] studied the polymerization oflinseed oil via calorimetry. They observed that all ofthe pigments such as minium (Pb3O4), chromiumyellow (PbCrO3) and red earth (based on ironoxides) accelerate the polymerization reaction oflinseed oil and therefore have a catalytic action.Kundu and Larock prepared a variety of newpolymers from conjugated linseed oil, styrene anddivinylbenzene by thermal polymerization [56]. Theresulting polymeric material was opaque and con-tained 35–85% of cross-linked materials. Thesecopolymers exhibited a major thermal degradation

of 72–90% at 493–500 1C. The thermogravimetricbehavior of some samples is shown in Fig. 25. All ofthe samples exhibited stability up to 100 1C, and thedegradation of the samples usually started around350 1C, with the whole mass degraded to char at500 1C and completely burned off at 650 1C.

2.6. Castor oil polymers

Epoxidized castor oil has been used for thepreparation of interpenetrating polymer networks(IPN), and these were characterized for theirdynamic mechanical behavior [57]. It was observedthat the cross-linked IPNs from the epoxidized oiland adducts of tung oil with maleic anhydride hadvery good compatibility. The hydroxyl groups ofepoxidized castor oil form hydrogen bonds with thecarbonyl groups in tung oil. These hydroxyls aremore reactive towards tung oil adducts thanepoxidized cottonseed oil. Yagci and coworkers

ARTICLE IN PRESS

Neat ENLO-1001% DEGDVE in ENLO-100 5% DEGDVE in ENLO-100 20% DEGDVE in ENLO-100

Irradiation Time (sec.)500 100 150 200 300250

Epo

xy C

onve

rsio

n (%

)

70

60

50

40

30

20

10

0

-10

Fig. 23. The effect of the reactive diluents, diethylene glycol

divinyl ether (DEGDVE), on the epoxy ring-opening polymer-

ization of sample ENLO-100 in the presence of 4 weight percent

(4-octyloxyphenyl) phenyl iodonium hexafluoroantimonate

(OPPI) as a function of the irradiation time. Reprinted with the

permission from J Polym Sci: Part A: Polym Chem 2003; 41: 3451

r Wiley Periodicals, Inc. [50].

Epo

xy C

onve

rsio

n (%

)

Neat ENLO-100

2 % DEGDEE in ENLO-100 6 % DEGDEE in ENLO-100 20 % DEGDEE in ENLO-100

70

60

50

40

30

20

10

0

-10

Irradiation Time (sec.)

500 100 150 200 300250

Fig. 24. The effect of non-reactive diluents, di-(ethylene glycol)

diethyl ether (DEGDEE), on the epoxy ring-opening polymeriza-

tion of sample ENLO-100 in the presence of 4 weight percent

(4-octyloxyphenyl) phenyl iodonium hexafluoroantimonate

(OPPI) as a function of the irradiation time. Reprinted with the

permission from J Polym Sci: Part A: Polym Chem 2003; 41: 3451

r Wiley Periodicals, Inc. [50].

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–10081004

prepared styrenated castor oil and linseed oil by themacromer technique [45].

Kumar and co-workers [58] oligomerized castoroil over molybdenum oxide on a silica–aluminasupport. They directly converted the methylricinole-

ate fatty acid ester into esters of dimer and oligomeracids. A fixed bed reactor was used for theoligomerization of dehydrated methylricinoleate.The product was characterized by infrared, 1H-NMR and mass spectroscopy. The kinetics of theoligomerization of methyl ester of dehydratedcastor oil fatty acid was compared with the thermaloligomerization process [59]. The catalytic reactionfollowed second-order kinetics, whereas the thermalprocess followed first-order kinetics.

Schwank et al. [60] reported the copolymerizationof dehydrated castor oil with styrene. The poly-merization was carried out in benzene and theproduct was isolated for characterization. It wasobserved that the copolymerization was verydifficult when the concentration of dehydratedcastor oil is more than 20%. Ashraf and coworkers[61] prepared a blend of dehydrated castor oil andepoxy resin. The miscibility of the two componentswas examined by viscometric and ultrasonic techni-ques. Ashraf and coworkers [62] also studied themiscibility of the blends of epoxidized dehydratedcastor oil and poly (methyl methacrylate). Thecompatibility was investigated by differential scan-ning calorimetry and SEM.

2.7. Polymers from other oils

Drying and semidrying oils such as sesame,sunflower, safflower, walnut oil have also beeninvestigated for the preparation of polymer bydifferent methods. Homopolymerization is notfavored due to the steric hindrance of the bulkyoil moieties. Triglyceride oil-based macromers ofsunflower oil were prepared in two successive steps[46]. First, a partial glyceride was prepared byglycerolysis of sunflower oil in the presence ofcalcium oxide (CaO). Subsequently, a macromerwas prepared by transesterification of the partialglyceride with methylmethacrylate in the presence ofthe same catalyst. The prepared macromer wascopolymerized with styrene in the presence ofbenzoyl peroxide, yielding a styrenated product. Inthis case, a product with longer polystyrenesegments was obtained.

Kusefoglu and coworkers [63] studied the poly-merization of high oleic sunflower oil with differentcomonomers. The effect of simultaneous addition ofbromine and acrylate to the fatty acid triglycerideswas studied. The yield for bromoacrylation ofsunflower oil was 55%. The copolymers of sun-flower oil and styrene were formed via free radical

ARTICLE IN PRESS

Photolysis of Photoinitiator

Ar 2I + X + [Ar

2I +X+] + ArI* + X*

ArI* + X* ArI + R + H*X*

Initiation

+ O

H+

H+

+O

O+

H

Propagation

O +

O+

O

HOO O

OO Homopolymer (I)

[g]

[b]

[c]

[d]

[f]

[a]

[e]

O + H O+

H O+

H O+

H O

HO

O

HO

O O+

O+

O

HO

O

OO O

Homopolymer (II)

[L]

[h]

[i]

[ j]

Scheme 7. The mechanism for the photoinitiated cationic polymerization of the epoxynorbornane linseed oil (ENLO). Reprinted with the

permission from J Polym Sci: Part A: Polym Chem 2003; 41: 3454 r Wiley Periodicals, Inc. [50].

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–1008 1005

mechanism. They also studied the polymerization ofacrylamide derivatives of fatty acid compounds [64].The acrylamide functionality on the triglyceride ofsunflower oil was introduced by the Ritter reaction.

3. Conclusion

In recent years, natural oils have become thecenter of attraction for their potential use as startingmaterials for the preparation of polymers. This is an

alternate route, which has the potential to augmentthe use of petroleum-based polymers. These trigly-ceride oils mostly comprise unsaturated fatty acids,and provide a wide scope for polymerization using avariety of techniques. The unsaturation present inthese oils makes them ideal for the preparation ofbio-based polymers. Polymers prepared fromsoybean oil have properties comparable with thoseof conventional polymers. The mechanical proper-ties of these polymers depend on the degree of

ARTICLE IN PRESS

0 100 200 300 400 500 600 700

0

20

40

60

80

100

Wei

gh

t lo

ss (

%)

C87

LIN30-ST28-DVB42 (S1)

C87

LIN40-ST24-DVB36 (S2)

C87

LIN50-ST20-DVB30 (S3)

C87

LIN60-ST12-DVB28 (S4)

C87

LIN70-ST08-DVB22 (S5)

Temperature (°C)

Fig. 25. The temperature dependence of the weight loss during

the thermogravimetric analysis of different samples prepared

from 87% conjugated linseed oil (C87LIN), styrene (ST)

and divinylbenzene (DVB). Reprinted with the permission

from Biomacromolecules 2005; 6: 805 r American Chemical

Society [55].

V. Sharma, P.P. Kundu / Prog. Polym. Sci. 31 (2006) 983–10081006

cross-linking; increased cross-linking increases theultimate strength and decreases the elongation atbreak. The dynamic mechanical properties of somenatural oil polymers suggest that they are idealreplacements for petroleum-based polymers, i.e.,some natural oil derived polymers possess very gooddamping and shape-memory properties over a widerange of temperature. The fatty acid ester groupsdirectly attached to the polymer backbone arepresumed to be responsible for damping properties.Damping materials have numerous applications inthe aircraft, automobile, and machinery industriesfor the reduction of unwanted noise as well as theprevention of vibrational fatigue failure. Shape-memory materials have applications in civil con-struction, mechanics and manufacturing, electronicsand communications, printing and packaging,medical equipment, recreation and sports, andhousehold items.

The polymerization of these oils is carried out viafree radical and cationic polymerization reactions.Different research groups in the world are studyingthe properties of natural oils and their compositesfor utilization as polymers, resins, varnishes andpaints. The fossil-based monomers are harmful toenvironment. These are non-renewable as they arederived mainly from petroleum-based materials.The fossil-based feedstocks are depleting veryrapidly. Thus, the main goal for the researchers incoming years is to produce viable polymers from thenatural resources.

Acknowledgements

The authors are thankful to the chief editors ofthis journal for their kind suggestions and editorialcorrections.

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