Crosslinking of polymers with azo-esters

Claim 1

The process of crosslinking or simultaneously cross-linking and foaming a polymer selected from the group consisting of polyethylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, acrylonitrile-butadiene-styrene rubber, ethylene-propylene-ethylidene-norbornene rubber, and polybutadiene rubber comprising: (a) mixing with 100 parts by weight of said polymer 0.5 to 20% by weight of a composition including at least one azo-ester cross-linking and foaming agent of the formula: ##STR19## in which R is selected from the group consisting of H, lower alkyl, cycloalkyl, aryl and aralkyl; R 1 and R 2 are independently selected from the group consisting of alkyl, cycloalkyl, aryl and aralkyl wherein each of the groups may have alkyl branching; R 1 and R 2 can join together to form R 1 R 2 group where the group is selected from --(CH 2 ) 4 --, --(CH 2 ) 5 --, alkylsubstituted tetramethylene or alkyl-substituted pentamethylene; R and R 1 can join together to form RR 1 group where the group is selected from --(CH 2 ) 2 --, --(CH 2 ) 3 --, alkylsubstituted --(CH 2 ) 2 -- or alkylsubstituted --(CH 2 ) 3 --; and R 3 is selected from the group consisting of --OOC--R, alkyl, cycloalkyl and aralkyl; and (b) in the absence of an activator which lowers the decomposition temperature of the cross-linking and foaming agent when the composition is heated, heating the polymer mixture at a temperature above 170° C. but not to the point where the polymer will substantially degrade and a pressure of 0 to 300 psia until cross-linking or crosslinking and foaming are effected.