The effect of hard and soft segment composition and molecular architecture on the morphology and mechanical properties of polystyrene–polyisobutylene thermoplastic elastomeric block copolymers

This paper reports the effects of hard (polystyrene, PS) and soft (polyisobutylene, PIB) segment composition and the molecular architecture (linear versus star, PS and PIB block length) on the morphology and mechanical properties of polystyrene/polyisobutylene (SIBS) block copolymers synthesized by living carbocationic polymerization. Atomic force microscopy, dynamic mechanical thermal analysis and tensile testing verified the phase-separated nature of the block copolymers, which behaved as thermoplastic elastomers (TPEs). The morphology of these TPEs is similar to polydiene-based TPEs, and is defined by the soft/hard segment composition. Interestingly, topology (linear vs star) did not have a major influence on morphology. Tensile testing showed that for both linear and three-arm star block copolymers, the modulus and tensile strength increased while elongation at break decreased with higher PS content. However, three-arm star block copolymers showed larger moduli than their linear homologues with similar PS content and PIB arm length, indicating the influence of molecular architecture on mechanical properties. These results might serve as a foundation for macromolecular engineering design for optimizing properties.