Copolymers of n-butyl acrylate and methyl vinyl ketone can be cross-linked by a combination of sulphur and zinc oxide; the reaction is associated with the methyl vinyl ltetone units in the polyn~er chain. From studies on the copolymers and model conlpounds, it is suggested that adjacent pairs or groups of methyl vinyl ketone units in the polymer cyclize t o give ap ~~n s a t u r a t e d ltetone groups. These contain reactive hydrogen which is attacked by sulphur; disulphide or zinc mercaptide cross-linlts are then formed. Water is produced in the cyclization reaction and hydrolyzes some of the ester groups; additional cross-links are thus formed by reaction of the acid groups with zinc oxide. The ease of cyclization and, therefore, the extent of cross-linking is dependent on the method of preparing the copolynlers, emulsion copolymers being much more reactive than those prepared in solution. A comparison has been made between the sulphur +zinc oxide system and other cross-linking agents which may be ~~s e d for polyacrylates.
The preparation and properties of copolymers from unsaturated ketones with acrylate esters and with butadiene are described. Details of the polymerization reactions and the structure of the copolymers are given. The preparation and properties of compounded vulcanized polymers are described and, in the case of the ketone-acrylate copolymers, the mechanism of sulfur vulcanization is discussed.
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