SPECIFIC HEAT OF SYNTHETIC HIGH POLYMERS .13. AMORPHOUS POLYSTYRENE

Using an improved differential-scanning calorimeter, a careful comparison of the specific heats of a number of amorphous samples of atactic and isotactic polystyrene has been carried out at a heating rate of 5° min-1. A molded and quenched sample of Dow atactic polystyrene has a 7% lower specific heat above Tg than a carefully annealed sample and this difference was maintained up to 150° during the 10-20 min required for the measurements. However, a standard sample of atactic polystyrene from the National Bureau of Standards did not exhibit this effect. Both polystyrene samples had the same specific heat above Tg after annealing. The lowered specific heat of the quenched sample is explained on the basis of strains existing in the sample which in terms of the Gibbs-DiMarzio theory raised E0, the intermolecular energy, 200-300 cal mol-1. Amorphous isotactic polystyrene from the Monsanto Co. did not crystallize during the specific heat measurements (from 50 to 260°) whereas that from the Dow Chemical Co. did.