Copolymers of butadiene and unsaturated acids: Crosslinking by metal oxides

Abstract

Abstract Butadiene copolymers of low molecular weight containing combined acid groups react with metal oxides to give products with unusual properties. The salts, particularly the zinc and cadmium compounds, exhibit plastic flow under slowly applied stresses but are highly elastic on sharp impact; products closely resembling the silicone “bouncing putty” can be obtained. Although these salts contain many “crosslinks” per chain they are, within limits, soluble in solvents such as benzene or pyridine. The solubility is determined by the molecular weight of the copolymer, its acid content, and the nature of the metal ion. Their solutions are characterized by marked changes in viscosity on dilution and they develop osmotic pressures in dilute solution comparable to those from the unreacted acid copolymers. The high molecular weight polymers are strong elastomers which show marked creep under stress. The properties of salts of both high and low molecular weight copolymers are consistent with the view that exchange reactions can occur between ionic crosslinks on different chains when stressed or under the influence of solvents. This ability to relieve local stresses on stretching is thought to be of consequence when considering the tensile properties of these and other elastomers.