Crosslinking of copolymers of N‐methylolacrylamide and ethyl acrylate induced by heat treatment

Abstract

AbstractThe effects of crosslinking by N‐methylolacrylamide in emulsion copolymers with ethyl acrylate under heat treatment in acid medium was investigated, and various methods for calculating the effective density of crosslinking were compared. It was found that stress‐strain relationships of copolymer films showed marked dependence both on the temperature of cure and on the methylolamide group content of the polymer; these dependences can be attributed to the formation of crosslinkages between polymer chains. The effective densities of crosslinking (ρ) of the cured copolymer films were calculated according to three methods: (1) stress‐strain measurement in dry state (ρe); (2) stress‐strain measurement in acetone (ρe′); (3) measurement of the degree of swelling in acetone (sρe). Values of ρe must be corrected with values for polymer with an infinite degree of swelling by use of the empirical equation of Mooney and Rivlin, in order to eliminate such steric factors as polymer chain entanglements; this method was found to be the most rational of the three, since ρe′ and sρe had their respective faults. The effective densities of crosslinking were found to be proportional to the squares of the methylolamide contents of the polymers, and there was a linear relationship with −5/3 slope between the logarithms of the stress and the degree of swelling, satisfying the theoretical expression.