Dielectric relaxation behaviour and the ductile/brittle transition of polycarbonate

Injection moulded polydiancarbonate has been studied mechanically and dielectrically and compared with annealed and embrittled material. The two forms of polycarbonate differ by a factor of four in impact strength under plane stress conditions but there is no substantial difference in their low temperature dielectric β-relaxations. This contraindicates explanations of their different properties and of the toughness of polycarbonate exclusively in terms of local main chain motions. Approximately 17% of the total chain units are mobile in the glassy state. The β-process is resolved into two processes at low temperatures, and the molecular origins of these, and of the intermediate temperature relaxation at 80°C, are discussed. © 1978.