Effects of Molecular Weight of Reaction Media on Formation of Volatile Oligomers by Thermal Degradation of Polyisobutylene

Abstract

For the thermal degradation of polyisobutylene, the effects of physical factors such as pressure in the reaction vessel and volume and molecular weight of the molten polymer matrix constituting the reaction media on the formation of the volatile oligomers were examined by a kinetic approach with measurements of composition ratios for terminal monoolefins [(TTD)p, (TVD)p, (TTD)t, and (TVD)t)]. The observed values of the composition ratios [TTD]p/[TVD]p and [TTD]t/[TVD]t are kept constant independently of changes in the physical factors. On the other hand, the ratios [TTD]p/[TTD]t and [TVD]p/[TVD]t do not depend on pressure and initial mass of sample, but depend on the initial molecular weight of sample. These values decrease clearly as the initial molecular weight decreases. It could be deduced that the decrease in molecular weight of the matrix decreases concentration ratio of two types of terminal macroradicals ([Rp·]/[Rt·]). According to the proposed kinetics of a chain mechanism including diffusion-controlled termination, a marked decrement of the radical concentration ratio suggests that the rate of termination increases with decrease in molecular weight of the matrix and that resulting decrement of kinetic chain length depresses the formation of the primary terminal macroradical (Rp·) in the depropagation step.