Change in molecular weight distribution accompanying thermal degradation of isotactic polystyrene

The molecular weight distributions of isotactic polystyrene samples subjected to various degrees of thermal degradation were experimentally determined and compared with those derived theoretically for randoms scission of the polymer chains. Agreement between the theoretical and the experimental results was fairly good. It was found that the molecular weight distributions of the original and the thermally degraded isotactic polystyrene can be represented by the logarithmic normal distribution function. The degree of degradation is nearly linear with time. The scission of the main chains seems to occur at random up to 330°C. The activation energy for the thermal degradation of isotactic polystyrene at 290 to 330°C. was 42 kcal. /mole. The results of thermal degradation of the isotactic polystyrene were compared with those of the atactic polystyrene.