CROSS-LINKING OF COPOLYMERS FROM METHYL VINYL KETONE AND n-BUTYL ACRYLATE

Abstract

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 ketone units in the polymer chain. From studies on the copolymers and model compounds, it is suggested that adjacent pairs or groups of methyl vinyl ketone units in the polymer cyclize to give αβ unsaturated ketone groups. These contain reactive hydrogen which is attacked by sulphur; disulphide or zinc mercaptide cross-links 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 copolymers, 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 used for polyacrylates.