Copolymerization of styrene with [(2-methacryloyloxy)ethoxy]trimethylsilane

European PolymerJournal. Vol. t2. pp 601 to 604. PergamonPress 1976.Printedin Great Britain.

COPOLYMERIZATION OF STYRENE WITH

[(2-METHACRYLOYLOXY)ETHOXY]TRIMETHYLSILANE P. BAIAJ and G. NANABABU Indian Institute of Technology, Delhi Hauz Khas, New Delhi-l10029, India

(Received 8 January 1976) Abstract Styrene (monomer-I) has been copolymerized with [(2-methacryloyloxy)ethoxy]trimethylsilane. MesSiOCH2--CH2OOCC=CH 2, at temperatures between 60 and 100° using benzoylperoxide I Me as initiator. The compositions of the copolymers have been determined by silicon estimation; the reactivity ratios were calculated by the Fineman Ross method. Arrhenius parameters have been derived. The difference between the activation energies, (Etl El2) favour self-propagation for the styrene radicals, whereas AtrIAl2 favours cross-propagation. In the case of silane radicals, (E22 E2~) favours crosspropagation but A2,/A,~ favours self-propagation. The intrinsic viscosities and the thermal behaviours of the copolymers were also studied.

INTRODUCTION Copolymerizations of styrene with various vinylsilanes [1 8], e.g. vinyltriethoxysilane, vinyltrimethylsilane, trimethyl (p-vinylphenyl)- and trimethoxy(pvinylphenyl)silanes, have been investigated and the reactivity ratios determined. The effects of temperature on reactivity ratios in these systems appear not to have been studied. The effects of temperature on the copolymerizations of styrene with cinnamic acid and its esters [9 12] a n d with other m o n o m e r s 1-13 16] have been reported by many workers. The temperature dependence of reactivity ratios in the styrene-vinyltriacetoxysilane system has also been studied: it was found that rl(styrene) decreases with increase in temperature [17]. The studies have now been extended to the copolymerization of styrene (MI) with [(2-methacryloyloxy)ethoxy]trimethylsilane (M2) in the temperature range 6(~100 ~: using benzoyl peroxide as initiator. EXPERIMENTAL

Materials Styrene (b.p. 26- 30/0.5 mm Hg) was obtained as middle cuts in reduced pressure distillation. 2-Hydroxyethylmethacrylate (E. Merck) was dissolved in dichloromethane and washed with aqueous sodium carbonate to remove methacrylic acid. The sample was then dried over anhydrous magnesium sulphate and distilled under reduced pressure. [2-(methacryloyloxy)ethoxy]trimethylsilane was prepared from 2-hydroxyethylmethacrylate and trimethylchlorosilane in the presence of triethylamine[18]. Benzoyl peroxide (BDH) was uscd after recrystallization from methanol. Copolymerizations were carried out by mixing known amounts of styrene and 2-MAETMS in different proportions in a two-neck flask, equipped with reflux condenser and nitrogen gas inlet. Benzoyl peroxide (0.1~/wt,) was added to the reaction flask and the polymerization was done in a constant temperature bath at temperatures between 6(~100 . The required time of copolymerization, i.e. the time necessary to polymerize not more than 10% 601 )p.J. 12'9 a

of the mixture, was found by trial and error. The reaction mixture was then poured into dry petroleum ether (b.p. 40-60 °) to precipitate the polymer. The copolymers were purified by repeated precipitation with petroleum ether from benzene solutions. The purified samples were dried to constant weight at 50° under vacuum. The compositions of copolymers were determined from silicon contents estimated gravimetrically [19]. The intrinsic viscosities were determined in dry benzene in an Ubbelohde viscometer at 30 _+ 0.05 °. The softening ranges of the polymers were measured in capillaries with a temperature rise of about 5°/min. The i.r. spectra of the polymers were recorded in carbon tetrachloride between 400-4000cm t on a Unicam SP-1200 infrared spectrophotometer. The glass transition temperatures were determined on a Stanton Redcroft differential thermal analyzer with calcined alumina as reference and at a heating rate of 6°/min in nitrogen. Thermogravimetric analysis was done on a Stanton model HT-D thermobalance in static air at a heating rate of 6°/rain.

RESULTS AND DISCUSSION The reactivity ratios, rl(styrene) and r2(2M A E T M S ) were determined by the F i n e m a n - R o s s method [20]. Plots were made of copolymer composition against m o n o m e r composition for temperatures between 60 and 100 °. Figure 1 shows typical behaviour at 60°; reactivity ratios at various temperatures are given in Table 1. The reactivity ratios tend to a p p r o a c h unity i.e. the difference between rl and r2 is decreased with increase in t h e polymerization temperature. Thus the tendency towards r a n d o m copolymerization is enhanced with increase in the reaction temperature. Reactivity ratios for the styrene/2-hydroxyethylmethacrylate ( S t - H E M A ) system at 60 ° have been reported by Luskin and Myers [21]. The reciprocals of rl(styrene) in both systems, viz. S t - H E M A , (1/rl) = 1.7 a n d St-2 M A E T M S , ( l / r 0 = 0.84 indicates the higher reactivity of H E M A compared with 2 - M A E T M S towards polystyryl radical.

602

P. BAJAJand G. NANABABU 0.09

Col 8,0--

0.07 6.0 0.05

~" a.o

S

0.03 2.0

0.01 0

-Lc

[

0

2.0

I

I

6.0

4.0

F2/f

ASlrAS12

I

3.0

1.2

~

1,4

RT

where A is the frequency factor and E is the energy of activation; the subscripts '11' and '12' refer to selfpropagation and cross-propagation of the growing radical, ,,,M'~ respectively. In terms of the transition state theory, the relationship becomes r 1 --

2.9

1.0

E11-El2

A12

I

2.8 03K- I T

The Arrhenius relationship between reactivity ratio and temperature may be expressed as l n r I = l n All

I

2.7

8.0

Fig. 1. Fineman-Ross plot for styrene and [(2-methacryloyloxy)ethoxy]trimethylsilane; r~(styrene) = 1.18 __ 0.03 and r2(2-MAETMS) = 0.18 + 0.04 at 60 °.

In

I

2.6

1,6 -o

1.7--

I

2.7

2.6

I

2.8

2.9

I

3.0

03 K - I T

AHII-AH12

R

I

Fig. 2. Arrhenius plots for the reactivity ratios. (a) rl(styrene ) and (b) r2(2-MAETMS).

RT

where AS represents the entropy of activation and AH the enthalpy of activation for the propagation step. Figures 2a and 2b show the Arrhenius plots of the reactivity ratios; the Arrhenius parameters are given in Table 2. The difference in activation energy (Eli-E12) is small since El1 is 32.5kJ mole -1 [22]. The difference (Ell-E12) favours self-propagation of the polystyryl radical whereas the ratio of preexponential factors (A~/A~2) favours cross-propagation; for the 2 - M A E T M S radical, the difference

(E22-E.21) is

11.6 kJ m o l e - 1, favouring cross-propagation but (A2 JA21) favours self-addition. CHARACTERIZATION AND PROPERTIES

To ascertain the effect of silane monomer on the rate of polymerization and intrinsic viscosity of copolymers, copolymerizations were carried out at high conversions under identical conditions (Table 3). The

Table 1. Variation of reactivity ratios with temperature Monomer reactivity ratio

Polymerization temperature 60

70

80

90

100

rl(Styrene) rz(2-MAETMS)

1.18 + 0.03 0.18 + 0.04

1.05 _+ 0.02 0.26 + 0.04

1.04 _ 0.02 0.30 + 0.02

1.03 + 0.01 0.33 + 0.01

1.02 ___0.01 0.35 ___0.02

Table 2. Arrhenius parameters for reactivity ratios

Monomer

Differences in energies of activation (kJ mole- 1)

Styrene(M~) 2-MAETMS(M2)

-1.66 + 0.01 11.6 _ 0.2

Ratios of frequency factors 0.59 ___0,08 14.7 + 0.1

Differences in entropies of activation (JK- 1 mole- 1) -4.33 + 0.08 22.4 +__0.3

Copolymerization of styrene

603

Table 3. Copolymerization of styrene(M1) and 2-MAETMS(M2) in bulk to high conversions*

No.

M~, mole fraction of monomer

Conversion ~o

1 2 3 4

0.98 0.962 0.943 0.91

50 47 34 3l

Silicon ~o

M ~, mole fraction of M1 in copolymer

[r/] dl/g

Softening range

1.82 2.31 2.52 2.73

0.928 0,907 0.898 0,888

0.34 0.31 0.27 0.21

138 151 145 170 165 185 170,190

* Polymerization time, 240 min; temp. 70°, concentration of BZ20 2 0.1"/owt.

intrinsic viscosity of copolymers and the rate of copolymerization decreases with increase in the silicon comonomer content. This may presumably be due to the presence of the silane radical at the growing chain ends (,,,M2) which being less reactive than the polystyryl radical (,,-M]) hinders the propagation. The i.r. spectra of the copolymers show the typical absorption bands at 610 and 1185cm -1 due to v ( S i ~ ) and v as ( S i - - O - - C ) respectively. Characteristic bands at 2955 and 1260cm- 1 for the trimethylsilyl group also confirm the introduction of the silicon moiety in the polymers. There is an increase in the softening range of the copolymers as the silicon content increases. A similar trend has also been observed in the glass transition temperatures (Table 4). The higher value of T o of the copolymers as compared to polystyrene may be attributed to the introduction of side-groups bulkier than the phenyl ring. The thermal degradations of copolymers have been studied by thermogravimetry; the thermograms of polystyrene and (St-2-MAETMS) copolymers are presented in Fig. 3. The data in Table 5 show that the initial decomposition temperature (IDT) for the copolymers is lower than for polystyrene. However, beyond 30% weight loss, the trend reverses i.e. rate

Table 4. Glass transition temperatures of polymers

SI. No.

Polymer

Mole per cent of the silicon monomer

I 2 3 4

2-MAETMS St-2-MAETMS St 2-MAETMS Styrene

100 34.6 18.9 0

T, l 12 103 98 94

I00

80

6O

40

M____

2O

0 2OO

I

240

I

280

320

I

360

I

400

I

I

440

480

Temperature

Fig. 3. Thermograms for, --, polystyrene; - - - , 92.3mole~o styrene copolymer; . . . . . . . , 91.6mole~,~, styrene copolymer.

of decomposition of polystyrene is higher than that of St 2-MAETMS copolymer. The values of D max ° (maximum decomposition temperature) are slightly higher for copolymers than for polystyrene. It is known that polystyrene decomposes mainly by depropagation and the controlling factor in the mechanism of the degradation is the nature of the side-group attached to the carbon atom at which chain scission occurs [23], Introduction of the bulky electron-withdrawing side substituent ( - - C O O C H 2 C H 2 - - O S i M e 3 ) therefore may be responsible for the lower threshold or initial decomposition temperature.

Acknowledyement--The authors thank the Council of Scientific and Industrial Research (CSIR), Delhi for providing a Junior Research Fellowship to G. N. Babu.

Table 5. Thermogravimetric analyses of styrene-[2-(methacryloyloxy)ethoxy]trimethylsilane DT at different weight losses SI. No. I 2 3

Polymer* Styrene St 2-MAETMS St-2-MAETMS

m2, mole per cent

IDT?

0 7.7 8.4

260 240 228

10~o 20~o 30~ 40~ 50% 60~o 70°/,, 80% Dmax++ 310 322 327 330 336 344 352 368 290 308 318 332 340 350 358 372 302 316 330 338 346 356 362 372

338 344 347

IPDT~ 357 352 347

* St, Styrene; 2-MAETMS, [2-(methacryloyloxy)ethoxy]-trimethylsilane; t IDT, initial decomposition temperature; Dmax, maximum decomposition temperature; ff IPDT, integral procedural decomposition temperature.

604

P. BAJAJ and G. NANABABU REFERENCES

1. Z. M. Rzaev, L. V. Bryksina, Sh. K. Kyazimov and S. I. Sadikh-Zade, Vysokomolek. Soedin. Ser. A14, 259 (1972). 2. C. W. Lewis and D. W. Lewis, J. Polym. Sci. 36, 325 (1959). 3. C. E. Scott and C. C. Price, J. Am. chem. Soc. 81, 2670 (1959). 4. N. S. Nametkin, I. N. Kozhukhova, S. G. Durgar'yan and V. G. Filippova, Vysokomolek. Soedin. Ser. A13. 2085 (1971). 5. V. G. Filippova, N. S. Nametkin and S. G. Durgar'yan, lzv. Akad. Nauk SSSR, Ser. Khim. 1727 (1966). 6. Y. Iwakura, F. Toda and K. Hattori, J. Polym. Sci. A1, 6, 1633 (1968). 7. G. Greber and E. Reese, Makromolek. Chem. 77, 13 (1964). 8. G. Greber and J. Tolle, Makromolek. Chem. 67, 98 (1963). 9. C. A. Barson and M. S. Rizvi, Europ. Polym. J. 6, 241 (1970). 10. C. A. Barson and M. J. Turner, Europ. Polym. J. 9. 789 (1973). 11. C. A. Barson and M. J. Turner, Europ. Polym. J. 10, 917 (1974).

12. C. A. Barson and M. J. Turner, Europ. Polym. J. 10. 1053 (1974). 13. F. M. Lewis, C. Walling, W. Cummings, E. R. Briggs and F. R. Mayo, J. A~. chem. Soc. 70, 1519 (1948). 14. G. Goldfinger and M. Steidlitz, J. Polym. Sci. 3, 786 (1948). 15. K. F. O'Driscoll, d. macromolek. Sci. A3, 307 (1969). 16. A. Rudin and R. G. Yule, J. Polym. Sci. A1, 9, 3009 (1971). 17. P. Bajaj, Y. P. Khanna and G. N. Babu, J. Polym. Sci., to be published. 18. G. N. Antiopina and K. A. Andrianov, Plast. Massy. (4), 28 (1968). 19. R. C. Mehrotra and P. Bajaj, J. Oroanomet. Chem. 22, 41 (1970). 20. M. Fineman and J. D. Ross, J. Polym. Sci. 5, 259 (1950). 21. L. S. Luskin and R. J. Myers, Encyclopedia of Polymer Science and Techology, Vol. 1, Interscience, New York, p. 246 (1964). 22. M. S. Matheson, E. E. Auer, E. B. Bevilacqua and E. J. Hart, J. Am. chem. Soc. 73, 1700 (1951). 23. M. Blazso' and T. Szekely, Europ. Polym. J. 10, 733 (1974).