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 th ermal experiments a temperature of 400 degrees C for 10 s was used in order to ensure only partial pyrolysis, whilst in another series of ex periments 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 numb er-distributions of the oligomeric products observed have been compare d with those predicted statistically on the basis of random scissions. The results show that the total pyrolysis can be interpreted exclusiv ely 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 fa voured scissions occur near the ends of the molecules or secondary rea ctions take place which favour the production of lower oligomers.