Tough heterogeneous polymers

The usual brittle behavior in tension of glassy homopolymers such as polystyrene can be rectified by incorporating into them heterogeneities that effectively catalyse dilatational plasticity by promoting profuse crazing without the need for any significant distortional plastic flow. This procedure which had been practiced industrially on a large scale for several decades to produce high impact polystyrene has been founded on empiricism. It is now possible to construct model heterogeneous polymers having composite particles with prescribed morphologies by using blends and emulsions of block copolymers. In this way the thermal and elastic properties of composite particles in glassy polymers can be deterministically manipulated to govern their dilatational plastic deformation resistance and their strain to fracture to maximize toughness. Here we discuss the overall principles for toughening of glassy polymers by controlled crazing, and discuss three case studies for special heterogeneous polymers to demonstrate these principles.