Abstract
The internal friction and the dynamic modulus of isotactic polypropylene samples subject to varying degrees of pile irradiation have been studied at low audio frequencies and over the temperature range from 100Β°K. to over 400Β°K. The radiation dosages used varied from 5.4 Γ 10^17^ to 14 Γ 10^18^ nvt. For irradiation doses up to about 3 Γ 10^18^ nvt, one observed change is a decrease in the temperature at which the final upswing in damping and drop in modulus occurs, presumably as a result of defects produced in the crystallites by the irradiation. As the irradiation dose increases above 3 Γ 10^18^ nvt, all evidence of crystallinity is lost, and the internal friction peak which occurs in the neighborhood of 300Β°K. and which is associated with the glass transition of the amorphous regions moves to higher temperatures as a result of the increasing chainstiffening effect due to crosslinking. The secondary loss peak at 250Β°K. attributed to the motion of a small number of segments in the amorphous regions is found to increase in magnitude with increasing dose. The results of density determinations made before and after irradiation and also after subsequent exposure of the irradiated samples to melting temperatures and of solvent extraction studies of the irradiated samples confirm the simultaneous occurrence of crosslinking and of crystalline degradation upon pile irradiation of polypropylene samples.