Polystyrene Glasses under Compression: Ductile and Brittle Responses.

Polystyrene of different molecular weights and their binary mixtures are studied in terms of their various mechanical responses to uniaxial compression at different temperatures. PS of = 25 kg/mol is completely brittle until it is above its glass transition temperature . In contrast, upon incorporation of a high molecular weight component, PS mixtures turn from barely ductile a few degrees below its to ductile over 40° below . In the upper limit, a PS of = 319 kg/mol yields and undergoes plastic flow, even at = -70 °C. The observed dependence of mechanical responses on molecular weight and molecular weight distribution can be adequately rationalized by the idea that yielding and plastic compression are caused by chain networking.