Thermal Degradation of Fractionated High and Low Molecular Weight Polyisobutylene

A series of thermal degradation studies on polyisobutylene has been carried out at relatively low degradation temperatures using samples of high purity, both fractionated and unfractionated, and of both high and low molecular weight. Rate curves of the high molecular weight polymer show maximums while those of the low molecular weight polymer show large initial rates which steadily decrease with increased volatilization. Rates of degradation of all samples become similar with increased volatilization. Rate studies indicate strong random initiation with the initial rate of volatilization showing very little dependence on molecular weight. The drop in molecular weight with increased degradation and the lack of broad maximums at moderate values of conversion shows the influence of an appreciable amount of transfer and a low kinetic chain length. The rate of degradation is found to be much faster than that of polypropylene or polyethylene probably because polyisobutylene disproportionates and forms radicals more easily. Equations are suggested for these degradation reactions.