Polymer degradation. V. Changes in molecular weight distributions during sonic irradiation of polyisobutene

Gel permeation chromatography was used to follow changes in the molecular weight distribution of a polyisobutene, initial Mv = 466,000, during degradation induced by sonic irradiation. Seven samples taken at times of 200–163,500 sec. were studied. In general, a steady decrease in molecular weight was observed, although a bimodal distribution was present after 20,000 sec. irradiation. Various measures of inhomogeneity, Mw/Mn, U, etc., were examined. The function, σn/Mw, where σn is the standard deviation of the number distribution, is considered as a measure of the relative distribution. It is shown to be almost constant throughout the degradation.