Multicomponent Polymer Systems

26 Multicomponent Systems from Copolymers of Maleic Anhydride and Vinyl Monomers

Downloaded by UNIV OF MONTANA on September 30, 2014 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0099.ch026

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RAYMOND B. SEYMOUR, HING SHYA TSANG, ELVIS E. JONES, PATRICK D. KINCAID, and ASHWIN K. PATEL University of Houston, Houston, Tex. 77004

Macroradicals have been produced previously by the degradation or cleavage of macromolecules using energy sources, such as, heat, light, ultrasonics, electrical discharge, radiation, tension, compression and mastication of polymers. Macroradicals that are present during the propagation of free radical chains may be preserved if isolated from other free radicals or scavengers. The preparation of these macroradicals by the copolymerization of maleic anhydride and vinyl monomers in poor solvents and the production of block copolymers from these macroradicals are discussed. Data on the characterization of these block copolymers are also included.

iyj"acroradicals are thermodynamically stable and may be preserved indefinitely if isolated from other free radicals, telogens, or vinyl monomers. F o r example, trapped free radicals produced b y the irradiation of cellulose were detected in significant concentration after four years (9). Macroradicals are also present during the free radical chain propagation of vinyl monomers, but because of their kinetic instability i n the presence of monomers, telogens, or other free radicals they are seldom isolated. However, relatively stable macroradicals have been observed in the micelles present in the emulsion polymerization of vinyl monomers (29). Relatively stable macroradicals may also be produced i n the absence of oxygen or scavengers by radiolysis (8), photolysis (24), high voltage spark discharge ( 7 ) , heating (3), and a wide variety of mechanical techniques i n which the polymer chains are stressed. Present address: Aerospace Division, Bendix Corp., Ann Arbor, Mich. 2 Present address: Dow Chemical Co., Freeport, Tex. 1

418 In Multicomponent Polymer Systems; Platzer, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.


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Thus, macroradicals have been obtained by stretching fibers (20), deforming plastics by compression (37), ball m i l l grinding (11), freezing and grinding of polymer solutions (10), ultrasonic irradiation ( J ) , mastication (19), dispersion i n a microblender (25), and other mechanical techniques (36). M a n y reviews on the formation of macroradicals by degradative processes have also been published ( 5 , 1 2 , 1 3 , 1 6 , 3 3 ) . Relatively stable macroradicals are precipitated when they are i n soluble in their monomers. Thus, poly (vinyl chloride) has been obtained by a process in which the solid polymer was removed continuously as it precipitated from the monomer (23). These precipitated macroradicals have been described as "popcorn" (21) or trapped free radicals (22). Macroradicals obtained by the polymerization of acrylonitrile which have been widely studied (4) have been used to prepare block copolymers (35).

HILDEBRAND VALUES

Figure 1. Relationship of Hildebrand solubility parameter values to molecular weight for different homologs A: B: C: D:

1-alkenes 1-chloroalkenes methyl esters formates and acetates

E: methyl ketones F: 1-cyanoalkenes G: n-alkanols H: alkylbenzenes

In Multicomponent Polymer Systems; Platzer, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

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100 •

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2 Time

3 (hrs.)

Figure 2. Rate of copolymerization of maleic anhydride and styrene in different solvents A: benzene B: xylene C: cumene

D: methyl isobutyl ketone E: p-cymene F: acetone

Preparation of Macroradicals by Heterogeneous Solution Polymerization Relatively stable macroradicals have also been obtained by the polymerization of vinyl chloride (15) or by the copolymerization of this monomer with vinyl acetate (32) in poor solvents—i.e., by heterogeneous solution polymerization. Appropriate solvents for this type polymerization can be selected on the basis of Hildebrands solubility parameters ($) (14). Data for these solubility parameters have been tabulated (6) and can be estimated from Figure 1. Thus, it is possible to provide homogeneous solution polymerization systems providing the solubility parameters of the monomer, polymer, and solvent are known. Styrene and maleic anhydride were copolymerized by both techniques in the experiments described in this report. Information on both homogeneous (17) and heterogeneous copolymerization of maleic anhydride and vinyl monomers is available (30).



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The latter technique is more rapid than the former (27, 31). In 1930 Wagner-Jauregg showed that alternating copolymers are obtained when maleic anhydride is copolymerized with vinyl monomers (34). This is true for copolymerization in good solvents, but when the molar ratio of styrene to maleic anhydride is greater than 1, styrene may add to the alternating copolymer in poor solvents to produce block copolymers. As shown i n Figure 2, the rate of the heterogeneous copolymerization of styrene and maleic anhydride in benzene (8 = 9.2) is faster than the homogeneous copolymerization of these monomers in acetone (8 = 9.9). However, this rate decreases as the solubility parameter values of the solvents decrease in heterogeneous systems. Thus, the rate of copolymerization decreases progressively in xylene (8 = 8.8), cumene (8 — 8.5), methyl isobutyl ketone (8 = 8.4), and p-cymene (8 = 8.2). A l l of these rates were faster than those observed in homogeneous systems. The solubility parameter of the alternating styrene-maleic anhydride copolymer was 8 = 11.0. The slow rate of copolymerization in acetone was related to the ease of termination of macroradicals by coupling. This coupling was hindered by the coiling of the macroradical chains in benzene, but propagation continued to take place since the monomers were able to pene1,820 2,933 4,960 7,540 12,140 19,740

r

131,500 212,500 344,000 531,000

Figure 3. GPC molecular weight data for poly(styrene-co-maleic anhydride) copolymerized in acetone



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Figure 4. Molecular weight data for poly(styrene-co-maleic anhydride) copolymerized in benzene trate the coils. Lower molecular weight macroradicals precipitated i n the poorer solvents, and the propagation was progressively hindered as the coils became tighter i n these poorer solvents. The shift from homogeneous to heterogeneous copolymerization was also noted in acetone—benzene mixtures. The rate was slow, and the system was homogeneous when a benzene (50) -acetone (50) mixed solvent (8 = 9.6) was used, but rapid heterogeneous copolymerization was observed in a benzene (80)-acetone (20) mixed solvent (8 = 9.3). As shown b y the gel permeation chromatograms i n Figures 3 and 4, the copolymer obtained from homogeneous copolymerization i n acetone had a lower average molecular weight and a narrower molecular weight distribution than that obtained by heterogeneous copolymerization i n benzene under similar conditions. Thus, the weight average molecular weight of the copolymer obtained from acetone was about 40,000 and that from benzene was about 70,000. Some of the difference i n average molecular was attributable to the continued propagation of the precipitated macroradicals. In addition, some coupling of the macroradicals probably occurred when they were dissolved i n tetrahydrofuran to obtain the gel permeation chromato-



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graphic data. Thus, as shown i n Figure 5, a lower average molecular weight was observed when a solution of hydroquinone i n tetrahydrofuran was used as the solvent. Comparable results were observed for the copolymerization of maleic anhydride and methyl methacrylate (8 = 10.8 for copolymer), methyl acrylate (8 = 10.7 for copolymer), and butyl methacrylate (8 = 10.7 for copolymer). However, the copolymers of maleic anhydride and stearyl methacrylate (8 = 10.3) and maleic anhydride and isobutyl methacrylate (8 = 10.4) have lower solubility parameter values, and hence, a slow homogeneous copolymerization was observed when these monomers were copolymerized with maleic anhydride i n benzene. Attempts to change the copolymerization of styrene and maleic anhydride i n benzene from a heterogeneous to a homogeneous process by using high concentrations of initiator or b y adding weak chain transfer agents, such as carbon tetrachloride, were unsuccessful. However, homo-

Figure 5. Molecular weight data for poly(styrene -co- maleic anhydride) copolymerized in benzene. Gel permeation chromatographic data obtained from THF solution containing hydroquinone


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geneous copolymerization was noted when 30 wt % nitrobenzene was added to the monomer mixture in benzene.


Preparation of Block Copolymers from Macroradicals The only product obtained by the copolymerization of styrene and maleic anhydride in acetone was the alternating copolymer even i n the presence of more than equimolar quantities of either styrene or maleic anhydride. However, as shown by the data in Table I, larger quantities were obtained than could be accounted for by the formation of the alternating copolymer when excess styrene was used for the copolymerization in benzene solutions. In addition to the precipitates, there was also a trace of benzene-soluble product, which was shown to be polystyrene by infrared spectrometric (28) and pyrolytic gas chromatographic techniques (26). Table I. Yields of Copolymers of Styrene and Maleic Anhydride Obtained by Heterogeneous Copolymerization in Benzene after 72 Hours at 50°C Molar Ratio of Styrene to Maleic Anhydride

Percent Yield in Excess of that Accounted for by the Alternating Copolymer

1:1 4:1 17:3 9:1 19:1

0 20 23 23 19

Unlike the alternating copolymer, these high yield benzene-insoluble products were not completely soluble i n acetone, but they were soluble in a mixture of acetone—benzene (2:1). However, unlike polystyrene, they were precipitated essentially completely when excess benzene was added to the acetone—benzene solutions. In contrast when excess benzene was added to a mixture of polystyrene and the alternating copolymer i n an acetone—benzene solution, the copolymer precipitated and the polystyrene remained in the benzene-rich solvent. The polystyrene was recovered from this solution by adding excess methanol. Typical chromatograms were observed when polystyrene was pyrolyzed in air and the pyrolytic products were analyzed by gas chromatography. A characteristic peak which was observed on the chromatograms obtained by the pyrolysis of maleic anhydride and the alternating styrene maleic anhydride copolymer but not with polystyrene was used as a reference peak. As shown in Table II, the ratio of the area under


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Table II. Relationship of the Ratio of Areas under a Styrene Peak to the Reference Peak in the Gas Chromatograms of the Pyrolytic Products Obtained from Copolymers of Styrene and Maleic Anhydride in Benzene Ratio of Areas under the Styrene Peak to the Reference Peak

Molar Ratio of Styrene to Maleic Anhydride

6.9 23.8 27.0 33.3 48.5


1:1 4:1 17:3 9:1 19:1

a styrene peak to this reference peak increased as the ratio of styrene to maleic anhydride i n the feed increased. It has been reported that pyrolysis gas chromatographic techniques could be used to differentiate between block and random copolymers (18). However, i t was not possible to distinguish between the block copolymers and mixtures of polystyrene and the alternating copolymers of styrene and maleic anhydride by the P G C technique used i n this i n vestigation. However, differences were noted i n the D T A thermograms of the alternating copolymer, the block copolymer, and the mixture of polystyrene and the alternating copolymer. It has also been reported that an aromatic carbon-hydrogen out of plane deformation band at 759 cm" was sensitive to sequence distribution i n styrene-maleic anhydride copolymers ( 2 ) . A shoulder was noted at this frequency i n the infrared spectra of the block copolymer, but it was not possible to demonstrate differences i n the spectra of the alternating and block copolymers with the instrumentation available. N o product was obtained when attempts were made to copolymerize styrene and maleic anhydride i n benzene at 50° C i n the absence of bisazoisobutyronitrile. Likewise, no free radicals were detectable when these solutions were examined using E P R techniques. Negative results were also noted i n solutions of the alternating copolymer prepared i n acetone. However, the presence of free radicals was noted when the alternating copolymer produced b y heterogeneous solution polymerization i n benzene was examined. This peak was observed with freshly prepared and aged copolymer samples that had been stored i n an inert environment. However, no peak was observed i n product that had been washed with methanol. The macroradicals obtained by the copolymerization of equimolar quantities of maleic anhydride and styrene were also used as initiators to form higher molecular weight copolymers and to prepare block copolymers. These macroradicals were effective as initiators after being stored for 180 hours at —20°C i n an oxygen-free atmosphere. However, 1



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they were readily deactivated when a good solvent such as acetone was added. As shown b y the gel permeation chromatograph i n Figure 6, the average molecular weight of poly(styrene-co-maleic anhydride) obtained by adding the macroradical to a benzene solution of the monomers was over 250,000. N o copolymer was obtained under comparable conditions in the absence of the macroradicals. Attempts to use these macroradicals to produce copolymers i n an acetone solution were unsuccessful. Macroradicals obtained by the copolymerization of equimolar quantities of styrene and maleic anhydride i n benzene or i n cumene were also used as initiators to produce block copolymers with methyl methacrylate, ethyl methacrylate, and methyl acrylate. The yields of these block copolymers were less than those obtained with styrene, but as much as 38% of methyl methacrylate present i n the benzene solution added to the macroradical to produce a block copolymer. The amount of ethyl methacrylate and methyl acrylate that was abstracted from the solution to form block copolymers was 35 and 20%.

Figure 6. Molecular weight data for poly(styrene-co-maleic anhydride) obtained in benzene using macroradicals as the initiator



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14 12

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MINS.

Figure 7. 1: 2: 3: 4:

Pyrograms of block copolymers

5: benzene acetone 6: toluene methyl acrylate methyl methacrylate 7: ethylbenzene ethyl methacrylate 8: styrene

The formation of block copolymers from styrene—maleic anhydride and acrylic monomers was also indicated by pyrolytic gas chromatography and infrared spectroscopy. A comparison of the pyrograms of the block copolymers in Figure 7 shows peaks comparable with those obtained when mixtures of the acrylate polymers and poly(styrene-co-maleic anhydride) were pyrolyzed. A characteristic infrared spectrum was observed for the product obtained when macroradicals were added to a solution of methyl methacrylate i n benzene. The characteristic bands for methyl methacrylate ( M M ) are noted on this spectogram i n Figure 8.



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I 2000

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1 , 1800

1 . 1600

1

. 1400

I - J 1200 CM"'

Figure 8. Infrared spectrum of block copolymer with methyl methacrylate Experimental Maleic anhydride was crystallized from sodium dried, thiophenefree benzene. T h e bisisobutyronitrile was crystallized from a mixed solvent containing equal volumes of benzene and toluene. T h e liquid monomers were purified by distillation under reduced pressure. Freshly distilled solvents were used. The copolymers were prepared b y the following method. Sufficient solvent was added to 0.5 gram of equimolar quantities of maleic anhydride and vinyl monomer and 0.0125 gram bisazoisobutyronitrile to make a total volume of 5 m l . The copolymerizations were conducted i n agitated sealed glass tubes i n the absence of oxygen. The product was recovered from homogeneous systems b y adding methanol i n a high speed blender. The precipitate was washed with methanol, filtered, and dried. The precipitate was removed from heterogeneous systems, washed well with fresh solvent after filtration and dried. The gel permeation chromatographs were obtained by eluting a 2% solution of copolymer i n a 10 A column manufactured by Water Associates. The calibration curve used to determine the molecular weights was obtained b y plotting elution volumes against projected extended chain lengths of polystyrene. Pyrolysis gas chromatographic investigations were made using a Wilkins model A100C aerograph equipped with a Servo-Ritter II Texas instrument recorder using helium as the carrier gas. The 10 ft X 1/4 inch diameter column was packed with acid washed chromosorb W (Johns Manville) with 2 0 % SE-20 (General Electric C o . ) . 4


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A rhenium tungsten code 13-002 pyrolyzing coil obtained from GowM a c Instrument C o . was used. Solutions of the samples were placed on the c o i l ; and the solvent was allowed to evaporate before the residual film was pyrolyzed for about 10 seconds. The infrared spectograms were obtained on a Beckman IR-10 instrument. Solutions or the styrene-maleic anhydride alternating copolymer and styrene block copolymer were used. A K B r pellet was used for the spectogram of the methyl methacrylate block copolymer.


Conclusions Macroradicals obtained b y the heterogeneous copolymerization of styrene and maleic anhydride i n poor solvents such as benzene were used to initiate further polymerization of selected monomers. This technique was used to produce higher molecular weight alternating copolymers of styrene and maleic anhydride and block copolymers. Evidence for the block copolymers was based o ç molecular weight increase, solubility, differential thermal analysis, pyrolytic gas chromatography, and infrared spectroscopy. Literature Cited (1) Allen, P. Ε. M., Downer, J. M. et al., Nature 177, 910 (1956). (2) Ang, T. L., Harwood, H. J., Polymer Preprints, ACS Div. of Polymer Chem. 5 (1), 306 (1964). (3) Arthur,J.C.,Hinojosa, O., Textile Res. J. 36, 385 (1966). (4) Bamford, C. H., Jenkins, A. D. et al., J. PolymerSci.34, 181 (1959). (5) Battaerd, H. A. J., Tregear, G. W., "Graft Copolymers," Interscience, New York, 1967. (6) Burrell, H., "Polymer Handbook," J. Brandrup, Ε. H. Immergut, Eds., Chapter 4, Interscience, New York, 1965. (7) Ceresa, R. J., "Block and Graft Copolymers," p. 97, Butterworth, London, 1962. (8) Chapiro, Α., Mankowski, Z., European Polymer J. 2, 163 (1966). (9) Dilli, S., Ernst, I. T., Garnett, J. L., J. Appl. PolymerSci.11, 836 (1967). (10) Dubinskaya, A. M., Butyagin, P. Yu,Vysokomol.Soedn. Ser. Β 9, 525 (1967). (11) Eckert, R. E., Maykrantz, T. R., Salloun, R. J., J. Polymer Sci. 6 B, 213 (1968). (12)

Gould, R. F., Ed., ADVAN. C H E M . SER. 66 (1967).

(13) Grassie, N., "Chemistry of High Polymer Degradation Processes," Aca demic, New York, 1956. (14) Hildebrand, J. H., Scott, R., "The Solubility of Nonelectrolytes," Reinhold, New York, 1949. (15) Imperial Chemical Industries, Ltd., British Patent 366,897 (1929). (16) Jelinek, H. H. G., "Degradation of Vinyl Polymers," Academic, New York, 1955. (17) Johnson, J. H., Schaefgen, J. R., "Macromolecular Synthesis," Vol. 1, C. C. Overberger, Ed., Wiley, New York, 1963. (18) Jones, C. E . R., Reynolds, C. E. J., British Polymer J. 1, 197 (1969). (19) Kraus, G., Rollmann, K. W.,J.Appl. Polymer Sci. 8, 2585 (1964). (20) Matthies, P., Schlag, J., Schwartz, E., Angew. Chem. 77 (7), 323 (1965).



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(21) Miller, G. H., Chock, E. P., J. Polymer Sci. 3A, 3353 (1965). (22) Morawetz, H., "Formation and Trapping of Free Radicals," A. M. Bass, J. P. Broida, Eds., Chapter 12, Academic, New York, 1960. (23) Pechiney-St. Gobain, Belgian Patent 647,821 (1964). (24) Ranby, B., Carstensen, P., ADVAN. CHEM. SER. 66, 256 (1967). (25) Radtsig, V. A., Butyagin, P. Yu., Polymer Sci. 9, 2883 (1967). (26) Seymour, R. B., Anderson, A., Thermochim. Acta 1, 137 (1970). (27) Seymour, R. B., Tatum, S. D., Boriack, C. J., Tsang, H. S., Texas J. Sci. 21,13(1969). (28) Seymour, R. B., Tsang, H. S., Warren, D., Polymer Eng. Sci. 7 (1), 55 (1967). (29) Smith, W. V., Ewart, R. H.,J.Chem. Phys. 16, 592 (1948). (30) Trautvetter, W., German Patent 968,130 (Jan. 16, 1958). (31) Tsuchida, E., Ohtani, V., Nakadai, H., Shinohara, I., Chem. Soc. Japan J. 70, 573-79 (1967). (32) Union Carbide Corp., U. S. Patent 2,075,429 (1937). (33) Walling, C., "Free Radicals in Solution," Wiley, New York, 1957. (34) Wagner-Jauregg, Ber. 63, 3213 (1930). (35) Yugi, M., Yayoi, O., J. Polymer Sci. 7A-1, 2547 (1969). (36) Zakrevskii, V. A., Baptizmanskii, Tomashevskii, E. E., Soviet Phys., Solid State 10, 1341 (1968). (37) Zhurkov, S. N., Zakrevskii, V. A. et al., Radiospektrosk Tverd Tela Dokl. Vser. Soveschch. Krasnoyarsh USSR 1964, 424 (c.a. 69) 36628 (1968). RECEIVED March 10, 1970.


Multicomponent Polymer Systems

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