Morphology-mechanical property relationship of a polystyrene-polybutadiene-polystyrene block copolymer and its blends with homopolymers

The morphology-mechanical property relation was investigated on a polystyrene-polybutadiene-polystyrene (SBS) block copolymer and its blends with polystyrenes (PS) and polybutadienes (PB) cast from a THF/MEK mixture (T/M) and a cyclohexane/benzene mixture (C/B). As-cast films with alternating lamellar morphology such as SBS (T/M) always show high moduli and “plastic-torubber” transitions, while those with PS-dispersed-in-PB-matrix morphology always exhibit low moduli and crosslinked rubberlike behavior. All these systems undergo strain-induced softening, accompanying breakdown of glassy PS domains, and show rubberlike behavior, regardless of the sample prehistory. However, upon annealing under adequate conditions, all these softened systems eventually revert to their original morphology and behavior.