Dienes, emulsion copolymerization rubber

We have considerable latitude when it comes to choosing the chemical composition of rubber toughened polystyrene. Suitable unsaturated rubbers include styrene-butadiene copolymers, cis 1,4 polybutadiene, and ethylene-propylene-diene copolymers. Acrylonitrile-butadiene-styrene is a more complex type of block copolymer. It is made by swelling polybutadiene with styrene and acrylonitrile, then initiating copolymerization. This typically takes place in an emulsion polymerization process. 

Today, a large part of the more than one billion lbs/year of impact polystyrene and 500 million lbs/year of ABS produced domestically is made by graft copolymerization. Impact polystyrene may be synthesized by dissolving a diene rubber in styrene monomer, in the presence or absence of another solvent, prepolymerizing the solution, and completing the polymerization in bulk, solution, or suspension. R. B. dejong describes a process wherein he prepolymerizes in emulsion with styrene as the continuous phase and the water as the dispersed phase and completes polymerization in aqueous suspension. 

Polymerization and Copolymerization of Dienes. Diene monomers can be polymerized to elastomers by bulk, solution, suspension, or emulsion processes. In commercial practice virtually all the diene elastomers are, however, prepared by the emulsion process. Some basic recipes used for preparing various types of synthetic rubber are shown in Table 15-17. 

The copolymerization of a,p-unsaturated ketones has been studied extensively in order to improve the poor chemical and thermal stability exhibited by the homopolymers. The vinyl ketones have been copolymerized with most of the common vinyl and diene monomers. The data are given in Ref. [326]. For initiation, the same reagents could be used as for free-radical homopolymerization. Copolymerization was carried out in bulk [371] and in emulsion systems [372]. In copolymerization with methyl methacrylate, vinyl acetate [373], and styrene [371] it was concluded that the relative reactivities of the vinyl ketones increase with the increasing electron-withdrawing nature of the vinyl ketone substituent. Polar and steric effects are not observed. Most of the work has been directed toward the preparation of oil- and solvent-resistant rubbers to replaee styrene-butadiene rubber. Emulsion eopolymerization of butadiene with methyl isopropenyl ketone yielded rubbers with good solvent resistance and low temperature flexibility, but the products tended to harden on storage and were not compatible with natural rubber [374]. The reactive earbonyl function caused sensitivity to alkine reagents. Copolymers of butylacrylate and methyl vinyl ketone, for example, can be erosslinked by treatment with hydrazine [375]. 

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