Stress, strain, and birefringence relations of swollen cis‐1,4‐polybutadiene crosslinked in solution

Stress–strain–birefringence relations are measured for a series of unswollen and swollen networks of cis‐1,4‐polybutadienes which differ both in the degree of crosslinking and in the volume fraction of rubber present during crosslinking. The stress optical coefficient (SOC), the Mooney–Rivlin constants C1, C2 and B1, B2 are calculated. Results show that the unswollen, solution‐vulcanized polymers have very low values of C2 and B2, but high SOC. Upon swelling with CCl4, the stress optical coefficients decrease considerably and agree well with the values obtained by Fukuda, Wilkes, and Stein, and by Ishikawa and Nagai. The networks prepared in solution exhibit different behavior from those crosslinked in dry state, suggesting that in order to understand the origin of deviations from kinetic rubber elasticity theory and the Kuhn–Grün birefringence theory, more consideration must be given to the effect of overall network topology on stress–strain–birefringence behavior.