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CHAPTER-3

SYNTHESIS AND CHARACTERIZATION

OF MONOMER AND POLYMERS

Scope of the chapter

This chapter gives a brief

description of synthesis and

characterization of bisfuran,

various bismaleimides, Diels-Alder

polyadducts, polyimides and bulk

polymerization products. It

also highlights the synthesis

and characterization of model compounds.

Chapter 3

Chemistry Dept., S. P. Uni., V. V. Nagar 47

3.1. SYNTHESIS AND CHARACTERIZATION OF BISFURAN

3.1.1. Introduction

A bicyclic heterocycle consists of two fused furan rings. DA reaction has been

applied to the furan heterocycle with growing frequency because of its

pronounced dienic character, which makes it particularly suited to intervene in

the DA cycloaddition reaction as the dienic partner. So many bisfuran have been

synthesized by the researchers for the synthesis of various polyimides. Not a

single report was found based on the synthesis of 2,5-bis(furan-2-ylmethyl

carbamoyl)terephthalicacid from pyromellitic dianhydride and furan-2-

ylmethanamine (furfurylamine). Hence, it was planned to undertake the study of

polyimides derived from bisfuran.

3.1.2. Experimental

3.1.2.1. Materials

All the chemicals and solvents used were of laboratory grade. Pyromellitic

dianhydride was purchased from Fluka Analytical-Japan. Furan-2-ylmethan

amine was obtained from local market and redistilled before use.

3.1.2.2. Synthesis of bisfuran

The bisfuran was synthesized by parity condensation of phthalic anhydride and

furan-2-ylmethanamine [1]. Adding drop wise a solution of furan-2-ylmethan

amine (0.2mol) to a stirred solution of pyromellitic dianhydride (0.1mole) and

keeping the temperature of the medium close to 0-5 ˚C for an hour (Figure 3.1),

thus obtained ensuing solution was poured into ice water in which the reaction

product precipitated. The final white precipitates were filtered, washed and

purified by column chromatography.

Figure 3.1: Synthesis of bisfuran

Chapter 3


3.1.2.3. Characterization of bisfuran

Table 3.1: Physiochemical, spectral and thermal parameters of bisfuran

Physiochemical parameters Molecular formula : C20H16N2O8

Molecular weight : 412.35 g.

Melting point : 250–260˚C (uncorrected)

Yield : 65 %

Color : white

Elemental analysis : % C % H % N Calc. 58.25 3.91 6.79

Found 57.87 3.75 6.58

Infrared spectral features (cm–1) 3528 cm–1 : –OH st. acid 3254 cm–1 : –NH st. amide 3123 cm–1 : –C–H st. furan rings 3038, 1627 cm–1 : –CH st. aromatic ring, –C–C– st. aromatic 2954, 2841 cm–1 : –CH st. aliphatic 1714, 1040 cm–1 : C=O st. acid, –C–O st.

1685 cm–1 : O=C–NH free amide 1581, 1465 cm–1 : –COO– asym. st., –COO– sym. st. 1500 cm–1 : backbone st. aromatic ring 1249, 1175 cm–1 : furan in–plane CH deformation

1H NMR spectral features 10.93 δ ppm : s 2H –COOH

8.90 δ ppm : t (J=5.2 Hz) 2H –NH–CO–

8.11 δ ppm : s 2H Ar.H

7.93 δ ppm : d (J=6.4 Hz) 2H H11,11’

7.75 δ ppm : t (J=6.4 Hz) 2H H10,10’

7.50 δ ppm : d (J=6.4 Hz) 2H H9,9’

4.32 δ ppm : d (J=5.2 Hz) 4H –CH2–

13C NMR spectral features 42.27, 117.73, 119.28, 123.47, 126.10, 129.32, 132.67, 135.70, 167.12,

172.73

Thermogravimetric analysis data Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.10 2.00 22.14 33.27 69.57 93.72 98.02

% wt loss due to decarboxylation (180–280˚C): calculated 21.34%. (first step) found 20.9%

Chapter 3


3.1.3. Results and discussion of bisfuran

To the best of our knowledge, 2,5-bis(furan-2-ylmethylcarbamoyl)terephthalic

acid (bisfuran) had not been reported previously. The characterization of the

reaction product provided the first unambiguous proof of the successful

synthesis of bisfuran.

1H NMR spectrum indicated the doublet peak at 4.32 δppm corresponded to

methylene group, doublet peak at 7.50 δppm, triplet at 7.75 δppm, doublet at

7.93 δppm and singlet at 8.11 δppm were attributed to six protons of furan ring

on H9,9’, H10,10’, H11,11’ and two protons of phenyl ring on H1,1’ respectively (Figure

3.2). The singlet at 10.93 δppm was ascribed to the protons of carboxylic acid

group and a triplet at 8.90 δppm attributed to the –NH proton of amide group,

which was further confirmed by 13C NMR values. In DEPT–135 spectrum of

bisfuran (Figure 3.3), the inverted peak at 42.24 δppm indicated the methylene

bridge between the amide and furan ring. Peaks due to substituted carbon of

aromatic rings and carbonyl carbon were not observed while the peaks due to

unsubstituted aromatic carbon were observed at 117.78, 119.24, 123.46 and

129.33 in DEPT–135 spectra, which were in favor of the proposed structure.

The FTIR spectrum of bisfuran showed the most relevant peaks of the furan ring

and 1,2,4,5–tetra substituted benzene ring (Figure 3.4), other than the typical

absorptions arising from the band at 3528 cm-1 and 1714 cm-1 for carboxylic

acid and 3254 cm-1 and 1685 cm-1 for O=C–NH group.

TGA data of bisfuran (Figure 3.5) indicated that, the degradation occurred into

two steps. First stage of degradation started from 180 ˚C to 280 ˚C might be

attributed to decarboxylation of bisfuran. The value of wt. loss 20.91% was

consistent with the theoretical value 21.34%. The second major stage at about

300˚C to 700˚C was attributed to the monomer decomposition/pyrolysis. The 3–

4% char residue remained at 700 ˚C.

The expected structure was thus clearly verified by this spectroscopic and

thermal analysis which indicated moreover the absence of any detectable

impurity, particularly of the two reagents used to prepare bisfuran. This was

additionally confirmed by elemental analysis (Table 3.1).

Chapter 3


Figure 3.2: 1H NMR of bisfuran

Figure 3.3: DEPT-135 of bisfuran

Chapter 3


Figure 3.4: FT–IR of bisfuran

Figure 3.5: Thermogram of bisfuran

Chapter 3


3.2. SYNTHESIS OF BISMALEIMIDES

3.2.1. Introduction

Bismaleimides (BMIs) are a class of compounds with two maleimide groups

connected by the nitrogen atoms via a linker, and are used as crosslinking

reagents in polymer chemistry. BMIs are a leading class of thermosetting

polyimides. Their excellent processability and balance of thermal and mechanical

properties have made them extremely popular in advanced composites and

electronics [2–3].

BMIs used in commercially available resin formulations are of lower molecular

weights and are based on cheap aromatic diamines which are crystalline

materials with high melting points.

A wide variety of BMIs has been synthesized with the aim of achieving unique

properties in resins and adhesives, for which they are mainly used. Almost every

aromatic amine (diamine) can be converted into the corresponding maleimide

(BMI).

3.2.2. Experimental

3.2.2.1. Materials

All the chemicals and solvents used were of laboratory grade. Maleic anhydride

was obtained from Merck laboratory ltd.-Mumbai. Various diamines viz., (1)

ethane-1,2-diamine (2) propane-1,3-diamine (3) butane-1,4-diamine (4) pentane

-1,5-diamine (5) hexane-1,6-diamine (6) 2-methylpentane-1,5-diamine (7) 2,2,4-

trimethylhexane-1,6-diamine (8) 3-(aminomethyl)-3,5,5-trimethylcyclohexan

amine (9) benzene-1,3-diamine (10) benzene-1,4-diamine (11) 4,4'-methylenedi

aniline (12) 4,4'-sulfonyldianiline (13) 4,4'-oxydianiline (14) 4,4'-methylenebis

(2-methylaniline) (15) 4,4'-methylenebis(2-ethylaniline) (16) 4,4'-methylenebis

(2-ethyl-6-methylaniline) (17) 4,4'-methylenebis(2,6-diethylaniline) used for the

preparation of bismaleimides were obtained from local market and used without

purification. Solvents were used of laboratory grade and distilled before use,

according to the standard procedures.

Chapter 3


3.2.2.2. Synthesis of bismaleimides

The synthesis of bismaleimides was developed originally by Searle [4–5].

Generally, bismaleimides were synthesized in two steps, the first step involving

the addition of one equivalent of various diamines to two equivalents of maleic

anhydride to form bisamic acid. The second step induced the cyclization of this

amic acid end-group through the joint intervention of anhydrous sodium acetate

and acetic anhydride (Figure 3.6).

Various bismaleimides BMI1–17 containing aliphatic, aromatic and alicyclic chain

in the backbone (Table 3.2) were synthesized as per the methods reported. All

synthesized bismaleimides were confirmed by their melting point.

Figure 3.6: Synthesis of bismaleimides

Table 3.2: List of bismaleimides

No. Structure of

bismaleimides Name

mp ˚C

M. Wt.

Ref.

BMI1

1,2-bismaleimido ethane

190 220 6, 7

BMI2

1,3-bismaleimido propane

194 234 8

BMI3

1,4-bismaleimido butane

196 248 8

BMI4

1,5-bismaleimido pentane

201 262 8

BMI5

1,6-bismaleimido hexane

139 276 6, 7

Chapter 3


BMI6

2methyl 1,5-bis maleimide

pentane

96 276 6, 7, 9

BMI7

2,2,4-trimethyl 1,6-bismaleimido

hexane

94 318 6, 7, 9

BMI8

isophorone bismaleimide

116 330 6, 7, 9

BMI9

1,3-phenylene bismaleimide

203 268 10,11

BMI10

1,4-phenylene bismaleimide

300 268 10,11

BMI11

4,4’- diamino diphenyl methane

bismaleimide

156 358 10,12

BMI12

4,4’-diamino phenyl sulfone bismaleimide

254 408 10,12

BMI13

4,4’- diamino diphenyl ether bismaleimide

179 360 10,12

BMI14

N,N'-(methylene bis(2-methyl-4,1-

phenylene) ) bismaleimide

195 386 7,13

BMI15

N,N'-(methylene bis(2-ethyl-4,1-

phenylene)) bismaleimide

210 414 7,13

BMI16

N,N'-(methylene bis (2-ethyl,6-

methyl-4,1-phenylene))

bismaleimide

165 442 7,13

BMI17

N,N'-(methylene bis(2,6-diethyl-4,1-

phenylene)) bismaleimide

160 470 7,13

Chapter 3


3.3. SYNTHESIS AND CHARACTERIZATION OF MODEL COMPOUNDS

3.3.1. Introduction

In order to facilitate the correct structural assessment and to be able to verify the

occurrence of the PIs, two model compounds were synthesized. Model

compounds 1 and 2 were prepared by using phthalic anhydride and furan-2-yl

methanamine thus obtained 2-(furan-2-ylmethylcarbamoyl)benzoicacid (0.01

mol) was reacted with equimolar amount of two different bismaleimides 1,2-bis

maleimidoethane (BMI1) and 4,4’-diamino diphenyl methane bismaleimide

(BMI11) designated as model compound 1 and model compound 2 respectively.

3.3.2. Experimental

3.3.2.1. Materials

All the chemicals and solvents used were of laboratory grade. Phthalic

dianhydride was purchased from E-Meark-Mumbai. Furan-2-ylmethan amine

was obtained from local market and redistilled before use. Bismaleimides BMI1

and BMI11 were prepared in our laboratory.

3.3.2.2. Synthesis of model compound

A suspension of 2-(furan-2-ylmethylcarbamoyl) benzoic acid (0.02mol) and

bismaleimides BMI1 and BMI11 in THF (0.01mol) was refluxed for 10h at 60˚C.

The resultant unaromatized and unimidized product was designated as DA

adducts. Adducts were refluxed at 150–160 ˚C for 4h with 2mL of acetic

anhydride to afford aromatization and imidization (Figure 3.7). The resulting

solution was cooled and poured into a large volume of water, washed, filtered

and then air dried. Thus obtained brown colored precipitates of aromatization

and imidization products were characterized by elemental analysis and IR

analysis.

Chapter 3


Figure 3.7: Synthesis of model compound

3.3.2.3. Characterization of model compounds

Characterization of model compounds was carried out using physico chemical

analysis and FT-IR analysis.

Chapter 3


Table 3.3: Physiochemical and FTIR spectral data of DA adduct of model compound 1



Yield : 75 %


Found 60.29 4.02 7.79

Infrared spectral features (cm–1) 3528, 3258, 3115, 3027, 2945, 2859, 1712, 1685, 1672, 1580, 1465,

1244, 1160, 1040 cm–1

Table 3.4: Physiochemical and FTIR spectral data of model compound 1



Yield : 60 %


Found 67.67 3.39 8.61

Infrared spectral features (cm–1) 3026, 2974, 2864, 1770, 1735, 1516, 1376 cm–1

Chapter 3


Table 3.5: Physiochemical and FTIR spectral data of DA adduct of model compound 2



Yield : 70 %


Found 66.44 4.19 6.55

Infrared Spectral Features (cm–1) 3539, 3248, 3110, 3041, 2963, 2852, 1785, 1732, 1710, 1676, 1580,

1460, 1241, 1162, 1069, 1044 cm–1

Table 3.6: Physiochemical and FTIR spectral data of model compound 2



Yield : 65 %


Found 72.56 3.67 7.15

Infrared spectral features (cm–1) 3028, 2972, 2862, 1771, 1730, 1513, 1379 cm–1

Chapter 3


Figure 3.8: FT–IR spectra of DAA of model compound 2

Figure 3.9: FT–IR spectra of model compound 2

3.3.3. Results and discussion of model compounds

The elemental analyses of the model compound 1 and 2 indicated that the

reactions had completed with good yields of cycloaddition of the furan rings and

were consistent with their predicted structures (Figure 3.7). The IR spectra of

the model compounds showed important changes with respect to those of the

initial monomers, which clearly confirmed that the Diels-Alder reaction and

Chapter 3


aromatization-imidization reaction had taken place with good yields with couple

of bismaleimides BMI1 and BMI11. The IR spectra of model compounds had

prominent characteristic bands of imide group (Figure 3.8).

3.4. SYNTHESIS AND CHARACTERIZATION OF DIELS-ALDER POLYADDUCTS

3.4.1. Introduction

Polymerization by Diels–Alder (DA) reaction is one of promising trends in the

preparation of polyimides (PIs). Studies on the application of the DA reaction

between furan (diene) and maleimide (dienophile) for the synthesis of novel

macromolecular materials had bloomed during the past few decades. DA

reaction is applied to the furan heterocycle with growing frequency because of

its pronounced dienic character, which makes it particularly suited to intervene

in the DA cycloaddition reaction as the dienic partner and the use of

bismaleimides as dienophiles is very useful because the double bond of

maleimide is very reactive towards electron rich dienes, to give a normal

demand DA cycloaddition [14]. The application of the DA reaction to furan

derivatives covers a large field of studies, dominated by synthetic aspects

following the importance by more recent surge of investigations in which the

dienophile counterpart to furans is a maleimide moiety. The first investigation

on PI through DA reaction involving a bisfuran and a bismaleimide monomer

combination was reported by Tesoro and Sastri [15]. DA reaction is prominent

example of click chemistry [16] that has been studied extensively in a variety of

contexts.

The experimental convenience associated with this range of temperatures,

together with the fact that side reactions and possible thermal degradation

mechanisms are negligible, that the furan/maleimide couple represents a highly

suitable choice for building a large variety of thermo reversible macromolecular

architectures. The important peculiarity of the DA reaction, apart from its click

connotation, is its reversible character. As a rough indication, the role of

temperature on the equilibrium, up to about 60 ˚C, the left–to–right DA

condensation to form adduct dominates, whereas above about 110 ˚C the retro–

DA adduct uncoupling becomes preponderant. The temperature is a key factor in

Chapter 3


determining the position of the equilibrium, which can be shifted heavily from

predominant adduct formation (DA reaction), up to 65 ˚C, to the predominant

reversion to its precursors (retro–DA reaction), above 100 ˚C [17].

Substitution of the furan have a profound effect on the ability of DA adduct to

retro DA as opposed to dehydrating to an aromatic ring. Highly electron donating

group on the 2-position of the furan enhances the forward DA reaction and also

inhibits the retro DA rection [18–19]. The forward DA reaction gives both endo

and exo stereoisomer adducts [20]. It does not play a significant role in the

macromolecular syntheses, since both participate in the chain growth [14]. The

pioneering work related to DA polymerization was done by Stille and Plummer

[21].

3.4.2. Experimental

3.4.2.1. Materials

Bisfuran and various bismaleimides were synthesized in our laboratory.

Laboratory grade THF was used.

3.4.2.2. Synthesis of Diels-Alder polyadducts

Synthesis of Diels-Alder polyadducts was carried out by using Diels-Alder

reaction between bisfuran (diene) and bismaleimides (dienophile).

Bisfuran and various bismaleimide (1:1 by mole) in an equal mole ratio were

dissolved in 50mL of tetrahydrofuran (Figure 3.10). This was refluxed for 10h at

60 ˚C. The resultant reaction mixture was cooled and poured into a large volume

of dry ether. The precipitates formed were filtered, washed and then air dried.

The obtained unaromatized and uncyclized products were designated as DA

adducts which were purified and characterized by elemental analysis, degree of

polymerization, number average molecular weight, FTIR and thermal analysis.

3.4.2.3. Characterization of Diels-Alder polyadduct

Characterization of Diels-Alder polyadduct (DAA1–17) was carried out using

spectroscopic, thermal and physicochemical techniques. Number average

Chapter 3


molecular weight (Mn) of polyimides was determined by non-aqueous conducto-

metric titration by method reported [22–24]. Results are given in Table 3.7–3.23.

Figure 3.10: Synthetic route for the synthesis of polyimides

Chapter 3


Table 3.7: Physiochemical, spectral, polymeric and thermal data of DAA1

Physiochemical parameters Empirical formula : C30H24N4O12

Empirical weight : 632.53 g.

Yield : 55 %

Color : light brown

Elemental Analysis : % C % H % N Calc. 56.96 3.82 8.86

Found 56.79 3.76 8.78

Polymeric analysis data Number average molecular weight ( Mn) : 4402±60

Degree of polymerization (DP) : 7

Infrared spectral features (cm–1)

3532 cm–1 : –OH st. (acid)

1715, 1464 cm–1 : –C=O st., –COO– st. (acid)

3033, 1503 cm–1 : –C–H st., backbone st. (aromatic)

2958, 2849 cm–1 : –C–H st. (aliphatic)

3256, 1674 cm–1 : –NH st., –C=O st. (amide)

1782, 1735 cm–1 : –C=O st. asym, sym (imide)

3122, 1586 cm–1 : –C–H st., –C=C– st. (furan)

1244, 1166 cm–1 : in plane –C–H deformation (furan)

1046 cm–1 : –C–O st.

916, 876, 734 cm–1 : out-of-plane –C–H deformation (furan)

881 cm–1 : C6H2 (1,2,4,5–tetra substituted benzene)


% weight loss : 0.4 1.2 14.2 24.3 42.7 80.9 95.4

% wt loss due to decarboxylation (180–280˚C): calculated 13.91 % (first step) found 13.5 %

Chapter 3





Yield : 50 %

Color : light brown


Found 57.51 3.96 8.60




3530 cm–1 : –OH st. (acid)








1040 cm–1 : –C–O st.



Thermogravimetric analysis data

Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.5 1.1 14.6 24.7 42.0 81.3 94.9


Chapter 3





Yield : 55 %

Color : light brown


Found 58.10 4.20 8.41



Infrared Spectral Features (cm–1)

3523 cm–1 : –OH st. (acid)








1045 cm–1 : –C–O st.




% weight loss : 0.6 1.1 14.0 24.1 42.2 80.0 95.1


Chapter 3





Yield : 55 %

Color : light brown


Found 58.67 4.42 8.23




3523 cm–1 : –OH st. (acid)








1041 cm–1 : –C–O st.




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.4 1.5 13.9 23.8 41.9 81.2 95.8


Chapter 3





Yield : 55 %

Color : light brown


Found 59.16 4.56 8.05




3523 cm–1 : –OH st. (acid)








1044 cm–1 : –C–O st.




% weight loss : 0.5 1.2 14.0 25.7 43.4 82.0 95.2


Chapter 3





Yield : 50 %

Color : light brown


Found 59.12 4.52 8.01




3529 cm–1 : –OH st. (acid)








1049 cm–1 : –C–O st.




% weight loss : 0.5 1.1 13.9 25.9 44.6 80.7 95.7


Chapter 3





Yield : 40 %

Color : light brown


Found 60.73 5.13 7.55




3527 cm–1 : –OH st. (acid)








1040 cm–1 : –C–O st.




% weight loss : 0.7 1.1 13.1 24.2 44.0 70.1 96.1


Chapter 3



Physiochemical parameters

Empirical formula : C38H38N4O12


Yield : 50 %

Color : light brown

Elemental analysis : % C % H % N

Calc. 61.45 5.16 7.54 Found 61.31 5.04 7.42




3533 cm–1 : –OH st. (acid)








1048 cm–1 : –C–O st.




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.4 1.2 12.8 23.9 42.0 80.9 95.0


Chapter 3





Empirical weight : 680.57g

Yield : 55 %

Color : brown


Calc. 60.00 3.55 8.23

Found 59.91 3.47 8.14




3520 cm–1 : –OH st. (acid)








1044 cm–1 : –C–O st.




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.4 0.8 13.5 24.0 47.1 71.3 95.2


Chapter 3




Empirical weight : 680.57g.

Yield : 55 %

Color : brown


Found 59.82 3.41 8.09


3529 cm–1 : –OH st. (acid)








1041 cm–1 : –C–O st.






Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.5 1.2 14.0 23.1 45.5 72.2 96.0


Chapter 3






Yield : 45 %

Color : light brown


Found 63.69 3.83 7.15




3526 cm–1 : –OH st. (acid)








1039 cm–1 : –C–O st.




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.4 0.8 11.7 20.0 47.2 74.1 95.2


Chapter 3




Empirical formula : C40H28N4O14S


Yield : 50 %

Color : light brown

Elemental analysis : % C % H % N % S Calc. 58.54 3.44 6.83 3.91

Found 58.38 3.28 6.69 3.76




3530 cm–1 : –OH st. (acid)








1035 cm–1 : –C–O st.



1368, 1142 cm–1 : –SO2 asym, sym


Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.5 1.2 11.2 21.0 45.5 72.8 96.3


Chapter 3





Yield : 50 %

Color : light brown


Found 61.89 3.44 7.07




3535 cm–1 : –OH st. (acid)








1235 cm–1 : –C–O–C– (aromatic)

1043 cm–1 : –C–O st.




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.5 1.0 11.3 20.5 45.3 72.1 96.3


Chapter 3





Yield : 55 %

Color : light brown


Found 64.54 4.18 6.89

Polymeric analysis data Number average molecular weight ( Mn) : 7188± 60



3529 cm–1 : –OH st. (acid)









1041 cm–1 : –C–O st.




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.4 0.8 11.7 23.8 47.0 74.0 95.0


Chapter 3






Yield : 50 %

Color : light brown


Calc. 65.37 4.63 6.78 Found 65.24 4.56 6.63




3533 cm–1 : –OH st. (acid)

1720, 1465 cm–1 : –C=O st., –COO– st. (acid) 3030, 1500 cm–1 : –C–H st., backbone st. (aromatic)


3269, 1665 cm–1 : –NH st., –C=O st. (amide) 1783, 1733 cm–1 : –C=O st. asym, sym (imide)

3122, 1585 cm–1 : –C–H st., –C=C– st. (furan) 1245, 1165 cm–1 : in plane –C–H deformation (furan) 1235 cm–1 : –C–O–C– (aromatic)

1043 cm–1 : –C–O st. 911, 870, 734 cm–1 : out-of-plane –C–H deformation (furan) 880 cm–1 : C6H2 (1,2,4,5–tetra substituted benzene)


% weight loss : 0.5 1.2 11.2 22.3 45.5 72.8 96.3


Chapter 3





Yield : 55 %

Color : light brown


Found 65.92 4.86 6.48




3536 cm–1 : –OH st. (acid)









1038 cm–1 : –C–O st.




% weight loss : 0.5 1.0 11.3 21.0 45.2 72.4 96.2


Chapter 3





Yield : 45 %

Color : light brown


Found 66.51 5.21 6.30




3530 cm–1 : –OH st. (acid)









1044 cm–1 : –C–O st.




% weight loss : 0.3 0.9 10.9 21.5 47.3 75.0 95.9


Chapter 3


3.4.3. Results and discussion of Diels-Alder polyadducts

3.4.3.1. Physical properties

The elemental analyses of the DA adducts (Table 3.7–3.23) indicated that the

reactions had reached good yield of cycloaddition of the furan rings and were

consistent with their predicted structures (Figure 3.10). The degree of

polymerization (DP) for the polymers was estimated by non-aqueous titration

were in the range of 7 to 9 (Table 3.7–3.23).

3.4.3.2. Spectral properties

IR spectral bands of the DA adducts suggested the formation of desired

compounds and supported their structure. Spectral features provide valuable

information regarding the nature of functional group attached. The IR spectra of

the adducts (Figure 3.11–3.13) showed important changes with respect to those

of the initial monomers, which clearly confirmed that the Diels–Alder reaction

had taken place with good yield with all the bismaleimides.

The IR spectra of DA adduct has prominent characteristic bands of furan, amide

and carboxylic acid groups. The bands near 3120, 1580, 1070 and 730 cm–1 were

attributed to furan ring attached to the benzene ring. The bands at around 3240

and 1680 cm–1 were attributed to amide groups, while the bands around 3530

and 1710 cm–1 were corresponding to –OH and –C=O group of carboxylic acid

respectively.

In order to varify the occurance of DA adducts, IR spectra of the DA adducts were

compared with the DA adducts of model compound and were found identical

with the DA adducts of model compound. These features confirmed the predicted

structure of unaromatized–unimidized DA adducts.

Chapter 3


Figure 3.11: FT–IR spectra of DA adducts DAA1


Chapter 3



3.4.3.3. Thermal properties

The thermal stability of DA adducts was evaluated from their TG curves (Figure

3.14–3.18). The mode of the thermal degradation in all DA polyadducts is found

to be almost similar. Thermogram of DA polyadducts indicated that, the

polyadducts were remaining unchanged upto 150 ˚C. All the DA polyadducts

underwent two stages of mass loss.

The first major stage was corresponded to the decarboxylation of the DA adducts

in the temperature range of 180–280 ˚C. This might be due to the

decarboxylation occurred in this range because of the carboxylic group is present

in the DA polyadducts. The values of wt. loss observed during decarboxylation

were quite consistent with the calculated values obtained from the proposed

structures.

The process of the second stage above 280 ˚C was due to polymer pyrolysis.

Comparative small amount of weight loss was observed between the

temperature ranges of 300–400 ˚C. A very rapid rate of weight loss was observed

between 400–600 ˚C. The char residue left at 700 ˚C was in the range of 4–6%.

Chapter 3


Figure 3.14: Thermogram of DA adducts DAA2–3

Figure 3.15: Thermogram of DA adducts DAA1,5–8

Chapter 3




Chapter 3



3.5. SYNTHESIS AND CHARACTERIZAION OF POLYIMIDES (PI1-17)

3.5.1. Introduction

Aromatic polyimide is an important class of high performance polymers due to

their excellent thermo-oxidative stability, mechanical strength, electrical

properties and high radiation and solvent resistance. They are condensation

polymers incorporating the imide group –CO–N–CO– in their repeating units

either as open chain or as rings and are generally derived from the reaction of

organic diamines with organic tetracarboxylic acids or their dianhydride.

Polymerization by Diels–Alder reaction is one of the promising trends in the

preparation of high performance polyimides. In this regard, a large number of

polymers have been developed which can be broadly categorized as either

thermosets or thermoplastics. Examples of thermosetting materials include

epoxies, polyimides and bismaleimides while the example of thermoplastic

materials largely consists of poly(sulfones), poly(ether–ether–ketones) and

poly(ether–imide).

Chapter 3


Our main concern was to synthesize novel polyimides, which possess

combination of thermoplastic and thermosetting moieties by introducing

bisfuran and bismaleimide segments. Introduction of bisfuran (bisamic acid/

pyromellitic part) segment is defined as a thermoplastic portion and

bismaleimide segment is defined as a thermosetting segment.

3.5.2. Experimental

3.5.2.1. Materials

All the solvents and chemicals used were of laboratory grade. All the DA

polyadducts DAA1-17 were synthesized in our laboratory. Acetic anhydride and

THF were purchased from S.D. Fine Chemicals, Mumbai.

3.5.2.2. Synthesis of polyimides

Novel polyimides containing thermoplatic-thermosetting merged segments were

derived from Diels-Alder polyadducts by simultaneous aromatization and

imidization using small quantity of acetic anhydride [15].

Aromatization of the polymers was carried out by refluxing 1 g of the dried

sample of DA adducts in THF with 2 mL of acetic anhydride for 4h at 160 ˚C.

Simultaneously, imidization reaction took place. The resulting solution was

cooled and poured into a large volume of water. The precipitates formed were

filtered, washed and then air dried. Thus obtained brown colored precipitates of

PIs were characterized by elemental analysis, IR analysis and by thermal

analysis. Synthetic route of polyimdes from DA polyadducts was scanned in

figure 3.10 and 3.19.

Chapter 3


Figure 3.19: Synthesis of polyimides PI1-17

3.5.2.3. Characterization of polyimides

Characterization of polyimides (PI1–17) was carried out using spectroscopic,

thermal and physicochemical techniques. Results are given in Table 3.24–3.40.

Chapter 3


Table 3.24: Physiochemical, spectral and thermal data of PI1




Yield : 45 %

Color : brown


Calc. 64.29 2.88 10.00

Found 64.12 2.71 9.89




1780 cm–1 : –C=O st. asym (imide)

1732 cm–1 : –C=O st. sym (imide)

1387 cm–1 : ϒ -C-N st. imide

1111, 722 cm–1 : ϒ (–C–N–C–) imide

1010 cm–1 : –C–H (aromatic)

1459, 881 cm–1 : C6H2 (1,2,4,5–tetra substituted benzene)


% weight loss : 0.7 1.4 3.1 17.6 42.8 67.3 94.9

Chapter 3






Yield : 45 %

Color : brown


Calc. 64.81 3.16 9.75

Found 64.72 3.09 9.67







1119, 721 cm–1 : ϒ (–C–N–C–) imide




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.3 1.0 2.9 14.8 44.6 62.4 94.9

Chapter 3






Yield : 45 %

Color : brown


Calc. 65.31 3.43 9.52

Found 65.24 3.37 9.44







1119, 724 cm–1 : ϒ (–C–N–C–) imide




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.2 1.0 3.2 15.4 45.0 63.2 96.2

Chapter 3






Yield : 45 %

Color : brown


Calc. 65.78 3.68 9.30

Found 65.71 3.60 9.24







1110, 722 cm–1 : ϒ (–C–N–C–) imide




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.3 1.1 3.2 15.1 45.0 62.6 95.8

Chapter 3






Yield : 40 %

Color : brown


Calc. 66.23 3.92 9.09

Found 66.12 3.87 8.98







1112, 729 cm–1 : ϒ (–C–N–C–) imide




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.8 1.9 3.8 18.5 46.0 65.7 96.4

Chapter 3






Yield : 50 %

Color : brown


Calc. 66.23 3.92 9.09

Found 66.09 3.81 8.94







1119, 720 cm–1 : ϒ (–C–N–C–) imide




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.6 1.3 3.3 15.9 45.9 63.9 95.2

Chapter 3






Yield : 45 %

Color : brown


Calc. 67.47 4.59 8.51

Found 67.34 4.47 8.43







1112, 729 cm–1 : ϒ (–C–N–C–) imide




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.7 1.3 3.5 19.3 47.3 63.9 95.8

Chapter 3






Yield : 40 %

Color : brown


Calc. 68.05 4.51 8.35

Found 67.93 4.39 8.26







1110, 722 cm–1 : ϒ (–C–N–C–) imide




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.8 1.5 3.3 20.1 43.9 65.9 96.7

Chapter 3






Yield : 50 %

Color : brown


Calc. 67.11 2.65 9.21

Found 66.92 2.50 9.08







1110, 720 cm–1 : ϒ (–C–N–C–) imide




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.5 1.0 1.1 7.0 34.3 70.9 96.2

Chapter 3






Yield : 45 %

Color : brown


Calc. 67.11 2.65 9.21

Found 67.00 2.52 9.16







1112, 720 cm–1 : ϒ (–C–N–C–) imide




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.3 0.9 1.2 8.0 35.1 69.9 95.9

Chapter 3






Yield : 40 %

Color : brown


Calc. 70.49 3.17 8.02

Found 70.28 3.03 7.89







1112, 729 cm–1 : ϒ (–C–N–C–) imide




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.2 0.6 1.3 6.0 34.2 71.2 96.3

Chapter 3




Empirical formula : C40H20N4O10S


Yield : 45 %

Color : brown

Elemental analysis : % C % H % N % S

Calc. 64.17 2.69 7.48 4.28

Found 63.97 2.48 7.31 4.19







1110, 722 cm–1 : ϒ (–C–N–C–) imide




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.4 0.4 1.1 6.9 33.1 68.9 95.7

Chapter 3






Yield : 40 %

Color : brown


Calc. 68.57 2.88 8.00

Found 68.45 2.73 7.89







1112, 729 cm–1 : ϒ (–C–N–C–) imide




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.6 0.8 1.5 8.0 34.9 70.3 96.8

Chapter 3






Yield : 45 %

Color : brown


Calc. 71.07 3.61 7.71

Found 70.94 3.54 7.64







1116, 726 cm–1 : ϒ (–C–N–C–) imide




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.2 0.6 1.3 7.0 33.8 71.2 95.9

Chapter 3






Yield : 45 %

Color : brown


Calc. 71.61 4.01 7.42

Found 71.53 3.90 7.35







1128, 720 cm–1 : ϒ (–C–N–C–) imide




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.4 0.5 1.1 7.9 33.2 68.9 95.7

Chapter 3






Yield : 40 %

Color : Brown


Calc. 72.11 4.38 7.16 Found 72.03 4.32 7.07







1112, 721 cm–1 : ϒ (–C–N–C–) imide




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.6 0.7 1.5 7.6 34.8 70.4 96.8

Chapter 3






Yield : 40 %

Color : brown


Calc. 72.58 4.72 6.91 Found 72.51 4.65 6.84







1111, 721 cm–1 : ϒ (–C–N–C–) imide




Temperature ˚C : 100 200 300 400 500 600 700

% weight loss : 0.3 0.5 1.2 6.3 31.2 68.1 95.4

Chapter 3


3.5.3. Results and discussion of polyimides

The thermoplastic-thermosetting merged polyimide system has been performed

by the Diels–Alder intermolecular reaction followed by aromatization of DA

adduct and imidization simultaneously.

3.5.3.1. Physical properties

The synthesized polyimides were brown in color. The elemental analyses (Table

3.24–3.40) of the polyimides PI1–17 indicated that the reactions had reached

good yield of aromatization and simultaneous imidization of the Diels–Alder poly

adducts and were consistent with their predicted structures (Figure 3.10, 3.19).

3.5.3.2. Spectral properties

IR spectral bands of the polyimides suggested the formation of desired

compounds and supported their structure. Spectral features provide valuable

information regarding the nature of functional group attached. The IR spectra of

the polyimides showed important changes with respect to those of the DA

adducts, which clearly confirmed that the aromatization and simultaneous

imidization reaction had taken place with good yield with all the DA adducts.

The IR spectra of polyimides have prominent characteristic bands of imide,

aromatic and aliphatic carbon. The bands near 3030, 1510 cm–1 were attributed

to aromatic ring. The bands at around 2950 cm–1 and 2830 cm–1 were attributed

to the aliphatic carbon, while the bands around 1785 cm–1 and 1730 cm–1 were

corresponding to the asymmetric and symmetric imide groups respectively.

While comparing the IR spectra of DA adducts and Polyimides (Figure 3.20–3.22)

significant differences were observed. The IR spectra of DA adducts have

prominent characteristic bands of furan, amide and carboxylic acid groups.

Comparison of the IR spectra of non aromatized and non cyclized DA adducts

(Figure 3.11–3.13) with aromatized and imidized (cyclized) polyimides (Figure

3.19) revealed discernible differences. The bands due to carboxylic acid and

amide groups in the spectra of DA adducts were almost disappeared in the

Chapter 3


spectra of polyimides, indicating that imidization reaction had taken place very

smoothly and the disappearance of the bands due to furan ring confirmed the

aromatization reaction had been completed simultaneously.

For the sake of convenience, the IR spectra of polyimides were compared with

the model compound (Figure 3.8). IR spectral features of polyimides were quite

identical with the model compound. These features confirmed the predicted

structure of aromatized-imidized polyimides.

Figure 3.20: FT–IR spectra of polyimide PI1

Chapter 3


Figure 3.21: Comparative FT–IR spectra of DAA14 and PI14

Figure 3.22: Comparative FT–IR spectra of DAA8 and PI8

Chapter 3


3.5.3.3. Thermal properties

Thermogravimetric analysis has emerged as one of the significant method for

assessing thermal properties of various materials in a different area of science. It

is most frequently used in the characterization of polymeric materials so as to

obtain the information not available by other techniques.

The thermal stability of polyimides was evaluated from their TG curves (Figure

3.23–3.27). During the thermal analysis, polyimides remain unchanged up to 400

˚C. It clearly confirmed that these polyimides were stable upto 400 ˚C. After this

temperature polyimides was decomposed. A very rapid rate of weight loss was

observed in DA adducts and polyimides at 400–600 ˚C.

The aromatized polyimides were more thermally stable as their pre polymers

(i.e. Diels–Alder polyadducts) had a nature of decarboxylation. Thus polyimides

(Figure 3.23–3.27) started their degradation at slightly higher temperature as

compared to non-aromatized samples (Figure 3.14–3.18). In case of polyimides,

decomposition started after 400 ˚C depending upon the nature of PIs. The char

residue left at 700 ˚C was in the range of 4–6 %. Examination of these data

revealed that the polyimides were more thermally stable than the DA

polyadducts.

Chapter 3


Figure 3.23: Thermogram of polyimide PI2–4

Figure 3.24: Thermogram of polyimide PI1,5–8

Chapter 3




Chapter 3



3.6. BULK POLYMERIZATION

A mixture of bisfuran (0.01mol), bismaleimides B1-17 (0.01mol) and 2 mL acetic

anhydride in THF were heated at 140–150 ˚C for 10h with vigorous agitation.

The resulting products were cooled and poured into a large volume of water. The

precipitates formed were filtered, washed and then air dried. The characteristics

of the obtained bulk polymerized products were consistant with the products

obtained by solution phase polyimides (i.e. synthesized polyimides).

Chapter 3


REFERENCES

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[4] Searle NE. 1948 U S Patent 2444536.

[5] Arnold HW, Searle NE. 1949 U S Patent, 2467835.

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[18] Thesis of Water John Francis 1993 Case Western Reserve University.

[19] (a) Taticchi F, Fringuelli A. 1990 Dienes in the Diels–Alder reaction. New

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Chapter 3


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