Stress‐Strain isotherms for stereoirregular and stereoblock cis‐trans polybutadienes

Gamma radiation and high‐energy electrons were used to crosslink two types of polybutadiene (PBD), the first having random cis‐trans‐vinyl contents and the second consisting primarily of blocks of cis units and blocks of trans. The resulting elastomers were studied in elongation in the unswollen stale, generally at 5°C, and in swelling equilibrium in a thermodynamically good solvent. Stress‐strain isotherms obtained for the random‐PBD networks did not show upturns in the reduced stress [f*] at high elongations, which is consistent with their non‐crystallizability. The stereoblock polymers were found to be crystalline, with melting points ranging from 14 to 65°C. Attempts to achieve strain‐induced crystallization in the stereoblock networks by judicious choice of temperature were unsuccessful as judged by the absence of any significant upturns in [f*]. Values of the elasticity constants 2C1 and 2C2, and the molecular weight between crosslinks were similar to those obtained from the linear portions of the isotherms previously reported for high‐cis and high‐trans PBD, which readily undergo strain‐induced crystallization. Copyright © 1986 Society of Plastics Engineers