On the Degradation of Branched Chain Molecules

Abstract

A procedure for the derivation of the molecular weight distribution in a degrading branched polymer is developed. In the explicit calculations only sizes up to about twice the distance between branch points are considered. This is adequate to describe the rates of volatilization in the pyrolysis of polyethylenes. Expressions are given for an arbitrary distribution of branch lengths. If the rate of bond scission is uniform, the over‐all rate is reduced in comparison with the linear case; the branches, if short, have a protective effect. The differences between C–H linkages on tertiary and secondary C's reverse the situation. However, the reaction pattern remains unchanged. The rates exhibit maxima which are only insignificantly displaced by the presence of (short) branches. Unless the reaction mechanism treated is profoundly altered or the differences between the two types of bonds are much larger than in small molecules, the existence of branches, per se, does not account for the observed differences in the kinetics of pyrolysis of polyethylene and the linear polymethylene.