Copolymers of p-biphenyl acrylate with methyl methacrylate: Synthesis, characterization and monomer reactivity ratios

Eur. Polym. J. Vol. 28, No. 9, pp. 1123-1126, 1992 Printed in Great Britain. All rights reserved

0014-3057/92 $5.00+0.00 Copyright © 1992PergamonPress Ltd

COPOLYMERS OF p-BIPHENYL ACRYLATE WITH METHYL METHACRYLATE: SYNTHESIS, CHARACTERIZATION A N D MONOMER REACTIVITY RATIOS D. MADHESWARI, S. NANZUNDAN and A. VENKATA RAMI REDDY* Department of Chemistry, College of Engineering, Anna University, Madras, India (Received 13 November 1991)

Abstraet~opolymers of p-biphenyl acrylate with methyl methacrylate were prepared in methyl ethyl ketone solution at 60° using benzoyl peroxide as initiator. The copolymers were characterized by i.r. and ~H- and ~3C-NMR; their compositions were determined by ~H-NMR analysis. The monomer reactivity ratios were determined by application of conventional linearization methods due to Fineman-Ross and Kelen-Tiid6s. The molecular weights of the polymers were determined by gel permeation chromatography. Tbermogravimetric analyses of the polymers were performed in air.

INTRODUCTION Poly(p-biphenyl acrylate (poly BPA) is known to exhibit liquid crystalline properties. Preparation and properties [1], chain configuration and molecular order [2] and X-ray studies [3] of the polymer have been reported. Thermotropic liquid crystalline properties of the polymer prepared by the reaction of poly(acryloyl chloride) with p-biphenol [4] have been given. Copolymers o f p - b i p h e n y l acrylate with N-(4biphenyl)acrylamide have been described [5]. The present paper reports the synthesis, characterization and determination of reactivity ratios for copolymers of BPA with methyl methacrylate (MMA). EXPERIMENTAL PROCEDURES MMA was freed from inhibitor by washing with 5% NaOH solution followed by distilled water, drying over anhydrous sodium sulphate and distillation under vacuum, Benzoyl peroxide (BPO) was recrystallized from chloroform-methanol mixture. BPA was prepared as reported [1]. All the solvents were distilled before use. Copolymerization

Copolymerizations were carried out in methyl ethyl ketone (MEK) solution at 60° using BPO as initiator. Appropriate amounts of MMA, BPA and MEK were mixed in a reaction tube and purged with N 2 for 20 min. After the sealed tubes had been kept at the required temperature, the contents were poured into a large excess of methanol. The polymers were purified by repeated precipitation by methanol from solution in chloroform and finally dried under vacuum. Measurements

Infrared spectra were recorded with a Hitachi 270-50 i.r. spectrophotometer on solid samples as KBr pellets. NMR spectra were obtained with a JEOL J N X - 100 FT NMR *To whom all correspondence should be addressed at: Central Salt & Marine Chemicals Research Institute, Bhavnagar 364002, India. EPJ 28/9~H

spectrometer. CDCI 3 and CHCI 3 were the solvents for tH= and ~3C-NMR respectively. TMS was the internal reference. Molecular weights (-£/w and -~'n) of the polymers were determined by gel permeation chromatography (Waters 501) equipped with a RI detector and calibrated with polystyrene standards. THF was the eluent. Thermogravimetric analysis was performed with a Mettler 3000 thermal analyzer at a heating rate of 15°/rain in air. RESULTS AND DISCUSSION The copolymerization of BPA with M M A in M E K solution was studied for molar fractions of BPA from 0.10 to 0.90 in the feed. The reaction time was selected to give conversions < 10 wt%, in order to satisfy the differential copolymerization equation. The data of compositions of feeds and copolymers are presented in Table 1. The copolymers were soluble in dimethylformamide, chloroform, tetrahydrofuran and dimethylacetamide but insoluble in nonpolar and hydroxy-group containing solvents (benzene, toluene, methanol and ethanol). The i.r spectra of the copolymers apparently show more prominent absorptions of BPA units since the absorption due to M M A overlap those of BPA. Strong absorptions at 1760 cm-~ were due to the carbonyl ( > C-----O) strechings. Peaks at 1603 and 1505 c m - 1 correspond to the aromatic > C------C< strechings. The out-of-plane C - - H bendings of the monosubstituted aromatic nucleus were observed at 700-780 cm -~ and those ofp-disubstituted nucleus at 815 and 840cm -1. The band at 1445cm -~ may be assigned to - - O C H 3 bending vibrations. JH-NMR spectrum (Fig. 1) of poly(BPA-coM M A ) shows resonance absorptions at 7.34 ppm corresponding to aromatic protons of BPA. Signals at 3.61 ppm were due to methoxy protons of M M A . A group of signals between 2.32-1.40 ppm may originate from backbone ----CH2 and - - C H protons. Signals at 0.87 ppm may be assigned to or-methyl protons of MMA.

| 123

D. MADI-/ESWARIet al.

1124

Table 1. Composition data of the free radical copolymerization of p-biphenyl acrylate (B) with methyl methacrylate (M) in MEK solution at 60° Sample No. 1 2 3 4 5 6 7

Feed MI 0.10 0.20 0.30 0.50 0.70 0.80 0.90

Conversion (%) 8.02 6.19 7.66 7.41 8.25 5.83 7.99

Figure

Copolymer mt 0.07 0.11 0.17 0.33 0.57 0.64 0.77

C 0.23 0.37 0.60 1.47 3.98 5.33 10.20

2

gives

the

13C-NMR

spectrum

polymers.

Copolymers compositions Since t h e c h e m i c a l s t r u c t u r e o f c o p o l y m e r s m a y be r e p r e s e n t e d as in Fig. 1, t h e a v e r a g e compositions of c o p o l y m e r s a m p l e s were d e t e r m i n e d f r o m t h e c o r r e s p o n d i n g ~ H - N M R s p e c t r a . T h e a s s i g n m e n t o f resort-

M~ and m I are the mole fractions of p-biphenyl acrylate in the feed and in the copolymer, respectively. Cis the ratio of the integrated intensity of aromatic protons to that ofmethoxy protonsin the ~H-NMR spectrum of the copolymer,

ance peaks allows accurate determination of the c o n t e n t of both kinds of monomeric unit in the

CH3 I

OCH 3

8

1

I

4

0

PPM Fig. 1. t H - N M R spectrum of poly(BPA-co-MMA).

--CHo--C--CN2--CH-"C=O

O=Cv 10 11

OCH3

14 15 -,11,16 o 15,- "-

4/8

9

t

]-~ 2,6 1

~"

I

170

of

poly(BPA-co-MMA). Chemical shift assignments were m a d e b y c o m p a r i n g t h e o f f - r e s o n a n c e d e c o u p l e d spectrum of the copolymers and the respective homo-

120 PPM

I

I

50

0

Fig. 2. Proton-decoupled 13C-NMR spectrum of poly(BPA-co-MMA).

Copolymers of p-biphenyl acrylate with MMA

/ / 0.8

-

0.2

-

-

.

/

<

///

, 0.4

0.4

1125

--

/

/

o

o

o

0 -0.2 t]

/

j

-o.4 -

0

I

I

0.4

0.8 M1

-0.6

Fig. 3. Composition diagram of BPA-MMA copolymer system. copolymer. Thus, the mole fraction of BPA in the copolymer chains was determined from the integrated intensities of aromatic protons o f BPA and methoxy protons of M M A . The following expression applies to copolymers, Let m~ be the mole fraction of BPA and (1 - ml) that of M M A . There are 9 aromatic protons in BPA and 3 methoxy protons in M M A . Therefore, 9m~ Intensities of aromatic protons 3(1 - m l ) = Intensities of methoxy protons = C (1) leading to C m~ = 3 + C '

(2)

F r o m equation (2), the mole fractions of BPA in copolymers were determined by measuring the intensities o f aromatic proton signals and methoxy proton signals. Table 1 gives the values o f C and the corresponding mole fractions of BPA in the copolymers. The plot o f mole fraction of BPA in feed vs that in the copolymer (Fig. 3) indicates that the distribution of monomeric units is statistical,

6 --

-1.0 0

I o.2

J o.4

I o.6

I 0.8

I 1.0

e Fig. 5. Kelen-Tiid6s plot for the BPA-MMA copolymer system. Reactivity ratios

F r o m the m o n o m e r feed ratios and the copolymer compositions, the reactivity ratios of BPA and M M A were determined by application of methods due to F i n e m a n - R o s s ( F - R ) [6] and Kelen-T/id6s ( K - T ) [7]. The values from the F - R plot (Fig. 4) and K - T plot (Fig. 5) are presented in Table 2. The product of rB and rM, indicates that this system copolymerizes statistically. The reactivity of growing radicals with M M A ends, as measured by l/rM, seems to be somewhat higher towards M M A than BPA. M o l e c u l a r weights The number- and weight-average molecular weights of poly(BPA) and three samples of copolymers, determined by gel permeation chromatography, are presented in Table 3. The polydispersity index of poly(BPA) and sample 1 is close to 1.5 and those of samples 2 and 3 are close to 2.0. The theoretical values of ~fw/J~f n for polymers produced

Table 2. Copolymerizationparameters for the free radical copolymerization of p-biphenyl acrylate with methyl methacrylate Method rs ru r B× r M l/r s I/rM Fineman-Ross 0.42 0.05 2.00 0.04 0.84 2.38 0.50 Kelen-Tiid6s 0.41 0.08 2.04 0.06 0.84 2.44 0.49 Average 0.41 0.07 2.02 0.05 0.84 2.41 0.50 % and rMare the reactivity ratios for BPA and MMA, respectively.

3 ~1 0

-3

0.8

0

J 6

I 12

I 18

J 24

F 2/f

Fig. 4. Fineman-Ross plot for the BPA-MMA copolymer system.

Table 3. Molecular weight data for the copolymers of p-biphenyl acrylate with methyl methacrylate Polymer MI /t;/w x 10 4 "~n x 10-4 /~'w/~r, Poly(BPA) 1.0 2.96 1.89 1.57 Copolymer I 0.9 2.47 1.51 1.64 Copolymer 2 0.5 2.89 1.59 1.82 Copolymer3 0.1 2.53 1.37 1.85 M~ is the mole fraction of BPA in the feed.

1126

D. MADH~SWARtet aL 100 --

- ~.

Table 4. TGA data for (p-bipheny]acry|ate)-(methylmethacrylate) copolymers Weight loss (%) at temperatures (°C) Polymer IDT 350 400 450 500 550

~,~,~

II I

--

a

, , ,, , b // I e , '.--~--~- - d

~e-"~ 50 ~t~

Poly(PBA)

350

--

1.2

4.7

35.3

95,3

Copolymer 1" 305 1.2 4.7 20.0 90.6 98.0 Copolymer 2* 280 3.5 10.6 55.3 95.3 98.2 Poly(MMA) 265 7.2 25.9 70.6 97.7 98.0 IDT, initial decompositiontemperature. *Copolymercomposition(mole fraction):(1) BPA/MMA:0.57/0.43; (2) BPA/MMA: 0.17/0.83.

/: //I, ,',, \.~\ o

I ape

~ 600

indicates that all the polymers undergo decomposition in a single stage. The initial decomposition temperature of poly(BPA) and poly(MMA) are 350 and 265 ° respectively; those of the copolymers are intermediate.

Temperature (*C) Fig. 6. TGA curves of: (a) poly(BPA); (b) poly(BPA-coMMA: 0.57/0.43); (c) poly(BPA-co-MMA: 0.17/0.83); and (d) poly(MMA). via radical recombination and disproportionation are 1.5 and 2.0, respectively [8]. In the homopolymerization of M M A , the radicals undergo termination mainly by disproportionation [9]. The value of .¢]w/~J'n in copolymerization is also known to depend on chain termination in the same way as in homopolymerization [10]. The values of ~tw/~t n of these polymers suggest a strong tendency for chain termination by disproportionation at high mole fractions of M M A and recombination at high mole fractions of BPA in the feed. Thermogravimetric analysis T G A curves for poly(BPA), p o l y ( M M A ) a n d two samples of poly(BPA-co-MMA) are shown in Fig. 6. The results of the differential thermogravimetric analysis are presented in Table 3. Figure 6 clearly

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