CRAZING IN 2 POLYSTYRENE-POLYBUTADIENE BLOCK CO-POLYMERS

In the reported experiments, crazing was investigated in two commercial polystyrene/polybutadiene block copolymers marketed under the trade names of KRO-1 and KRO-3 resins. The two block copolymers each with 23% polybutadiene (PB), have radically different microstructure and radically different crazing behavior, leading to strains to fracture of 0. 1 and 1. 0, respectively. Of these, the KRO-1 resin has a phase microstructure that consists of randomly wavy and often interconnected rods of PB of 20 nm diameter surrounded by polystyrene (PS). The microstructure of KRO-3 resin consists of lamellae of PB with 20 nm thickness and large aspect ratio which range in packing from regular aligned lamellar domains with randomly varying misorientation in the annealed material, to randomly corrugated and wavy sheets in the as-received material. The measured stress and temperature dependences of craze velocities in these two polymers is in partial support of the suggested mechanisms which are also developed in outline.