THE THERMAL-DEGRADATION MECHANISM OF POLYISOBUTYLENE .1. COMPARISON OF RESULTS WITH STATISTICAL PREDICTIONS PROVIDES A GENERAL INTERPRETATION OF THE MECHANISMS OF DECOMPOSITION

Samples of polyisobutylene (PIE) have been degraded thermally as thin films on a thermocouple-controlled filament. In one series of these thermal experiments a temperature of 400 degrees C for 10 s was used in order to ensure only partial pyrolysis, whilst in another series of experiments a temperature of 610 degrees C for 30 s was used to achieve complete pyrolysis. In both cases the yields and molecular weights of the products were assessed by gas chromatography. The weight- and number-distributions of the oligomeric products observed have been compared with those predicted statistically on the basis of random scissions. The results show that the total pyrolysis can be interpreted exclusively in terms of parallel depropagation and random scission mechanisms. However, the partial pyrolysis results are not consistent with random scission statistics but instead imply that either some kinetically favoured scissions occur near the ends of the molecules or secondary reactions take place which favour the production of lower oligomers.