POLYURETHANE ELASTOMERS STUDIED BY THE MOONEY-RIVLIN EQUATION FOR RUBBERS

A series of poly (ester-urethane) block copolymers were prepared via a two-step polymerization process. The prepolymer composition was kept constant in all the samples, while the NCO/OH ratio during extension was varied from 0.9 up to 1.2. By this way, chemical and physical cross-links were constructed into the materials. Equilibrium stress-strain measurements have been carried out for the examination of the elastomeric behavior of the materials tested. Calculation of an extra entropy term resulting from the network deformation is based on a first-principles derivation of the distribution function, taking into account a new type of network constraints. The process yields the Mooney-Rivlin equation and the constant C2 as a function of physical cross-links.