Macroradical styrene-maleic anhydride copolymer

Block Copolymers from Styrene-Maleic Anhydride Copolymer Macroradicals... 

For example, the styrene-maleic anhydride copolymer is soluble in acetone, and polyacrylonitrile is insoluble in acetone but soluble in dimethylformamide. Yet, the block copolymer obtained by addition of acrylonitrile to the styrene-maleic anhydride macroradical is soluble neither in acetone nor in dimethylformamide. Pyrolysis gas-chromatography, though, shows that this acetone and dimethylformamide-insoluble product contains styrene, maleic anhydride, and acrylonitrile. The relative area of the acrylonitrile peak was related to the amount of acrylonitrile added to the original macroradical. 

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 in benzene. The characteristic bands for methyl methacrylate (MM) are noted on this spectogram in Figure 8. 

The formation of block copolymers can result from the addition of excess styrene monomer to SMA macroradicals (13). Maleic anhydride has also been reported to homopolymerize when initiated by gamma-radlation of free radical Initiators. The highest conversions were obtained employing acetic anhydride as the solvent, in a ratio of solvent to monomer of 75 25 (14,15). 

New macroradicals have been obtained by proper solvent selection for the homopolymerization of styrene, methyl methacrylate, ethyl acrylate, acrylonitrile, and vinyl acetate, and by the copolymerization of maleic anhydride with vinyl acetate, vinyl isobutyl ether, or methyl methacrylate. These macroradicals and those prepared by the addition to them of other monomers were stable provided they were insoluble in the solvent. Since it does not add to maleic anhydride chain ends, acrylonitrile formed a block copolymer with only half of the styrene-maleic anhydride macroradicals. However, this monomer gave excellent yields of block polymer when it was added to a macroradical obtained by the addition of limited quantities of styrene to the original macroradical. Because of poor diffusion, styrene did not add to acrylonitrile macroradicals, but block copolymers formed when an equimolar mixture of styrene and maleic anhydride was added. 

Also, it has been reported that poly(styrene-co-maleic anhydride-b-styrene) could be obtained either by addition of styrene monomer to the styrene-maleic anhydride macroradicals or by the free-radical-initiated copolymerization of maleic anhydride with more than an equimolar proportion of styrene in benzene solution (7). However, the maximum amount of styrene present in these block copolymers was less than 35% of the weight of the original macroradical. This limitation on the yield of the block copolymer is now assumed to be related to the increased solubility of the styrene block in the benzene solvent, which permits termination of the new macroradicals by coupling. 

Block copolymers in good yield were obtained when the styrene-maleic anhydride macroradicals were heated with methyl methacrylate in benzene at 50°C. (see Figure 2). Unlike what happened when... 

The rate of block copolymer formation in a poor solvent is inversely related to the difference between the solubility parameters of the macroradical and the monomer used to form the block. Thus, when these solubility parameter values are similar—as with the addition of styrene and maleic anhydride to the styrene-maleic anhydride macroradical—a 100% weight increase is observed in a few hours. 

The difference between the solubility parameter of acrylonitrile and the styrene-maleic anhydride macroradical is 0.5 hildebrand unit. The formation of block copolymer was thus rapid, and the weight of these macroradicals increased by 86 percent in 24 hours in the presence of acrylonitrile (Figure 3). 

Acrylonitrile was also added to a mixture of benzene and macroradicals obtained from a monomer mixture containing equimolar amounts of maleic anhydride and styrene. Compared with the data already cited for styrene-rich macroradicals, only 50% of the macroradicals obtained from the equimolar mixture produced acetone-insoluble block copolymers. Since a mixture of maleic anhydride and acrylonitrile did not form a copolymer when heated with AIBN in benzene, it was concluded that half of these original macroradicals had maleic anhydride terminal groups. 

Dead copolymers, as noted, were obtained when large amounts of styrene monomer were added to styrene-maleic anhydride macroradicals. However, macroradicals were obtained when the amount of styrene added equalled less than 30% of the weight of the macroradical. For example, block copolymers were obtained when styrene and maleic anhydride or acrylonitrile were added to styrene-co-maleic anhydride-b-... 

However, an active benzene-insoluble methyl methacrylate-maleic anhydride macroradical was obtained when the molar ratio of the maleic anhydride to methyl methacrylate was 4 to 1. This random macroradical contained about 50% maleic anhydride. Excellent yields of block copolymers were obtained when mixtures of maleic anhydride and styrene or vinyl acetate were added to these macroradicals. For example, the ratios of the weight of the styrene-maleic anhydride and the vinyl acetate-maleic anhydride blocks to the weight of the macroradical were 790/100 and 627/100, respectively, after the mixtures of the monomers and the macroradicals were heated in benzene for three days at 50°C. 

Block (or graft) copolymers have been obtained by the addition of styrene and N,N-dimethylformamide (DMF) to acrylonitrile macroradicals, and add by the addition of methyl methacrylate or styrene to vinyl chloride macroradicalsBlock copolymers have also been produced by the addition of various vinyl monomers to styrene-maleic anhydride macroradicals (122) ... 

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 in an oxygen-free atmosphere. However,... 

As shown by the gel permeation chromatograph in 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. No copolymer was obtained under comparable conditions in the absence of the macroradicals. Attempts to use these macroradicals to produce copolymers in an acetone solution were unsuccessful. 

Macroradicals obtained by the copolymerization of equimolar quantities of styrene and maleic anhydride in benzene or in 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 in 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%. 

Macroradicals obtained by the heterogeneous copolymerization of styrene and maleic anhydride in 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 op molecular weight increase, solubility, differential thermal analysis, pyrolytic gas chromatography, and infrared spectroscopy. 

Compound 35 contains a thermolabile C-C bond which, on thermally induced fragmentation, yields a high proportion of macroradicals. The PDMS diradical also acts as a counter radical and can undergo chain extension at both ends in the presence of vinylic monomers (acrylonitrile, maleic anhydride, diethylfumarate) or styrenic monomers, leading to diblock copolymers in 95% yield according to the following scheme [211, 212] ... 

While it is assumed that termination by coupling takes place when maleic anhydride and styrene are copolymerized in a good solvent such as acetone, insoluble macroradicals precipitate when these monomers are copolymerized in a poor solvent such as benzene (7). Insoluble macroradicals obtained by bulk polymerization of acrylonitrile (1, 11) and the solution copolymerization of maleic anhydride and styrene in benzene (7) have been used as seeds for the preparation of block copolymers. 

Yields in excess of 98% of macroradicals were obtained in less than two hours when equimolar oxygen-free mixtures of maleic anhydride and styrene were heated at 50°C in the presence of 2.5% a, a -azobisiso-butyronitrile (AIBN). These macroradicals could be isolated by filtering in an inert atmosphere and removing residual solvent by applying a vacuum at 0°C. The macroradicals retained their ability to form block copolymers after being stored for seven days in the absence of oxygen at 0°C. 

However, the difference between the solubility parameters of an equimolar mixture of styrene and maleic anhydride and the acrylonitrile macroradical is only 1.1 hildebrand units. Thus, a block copolymer with a ratio by weight of styrene and maleic anhydride to that of the acrylonitrile macroradical of 41/100 was obtained when a mixture of these... 

Monomer pairs, one electron rich, the other electron poor, have been shown to form (CTC) s. Typical CTC s are formed from styrene and maleic anhydride and styrene and acrylonitrile in the presence of Lewis acids (23-25). These CTC s are known to rapidly polymerize in the presence of free radical initiators to form copolymers with a high degree of alternation (26,27). If the copolymerization is conducted in a poor solvent for the polymer, occluded macroradicals will be produced. 

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