Investigation of thermal degradation of polystyrene by differential scanning calorimetry

Thermal degradation of polystyrene was performed in a differential scanning calorimeter under nitrogen atmosphere, and the glass transition temperature was measured continuously. From random chain scission kinetics and Tg‐molecular weight relationships, the rate constant for random scission was obtained. The rate constant was found to undergo a drastic change at a critical molecular weight (∽45,000), which corresponds to a similar observation in relaxation studies. A viscosity‐dependent mechanism for radical chain end termination is thus suggested.