POLYMER DEGRADATION MECHANISMS - NEW APPROACHES

In studying the thermal degradation of polymers, experimental problems such as that of taking the samples rapidly to chosen degradation temp eratures can be solved by appropriate filament design and the use of s ufficiently small samples. The pyrolysis-GC technique can then provide reliable quantitative data which can be used in the following ways to obtain mechanistic information about degradation processes. (I) Depen dence of rate constants for volatiles evolution on the initial molecul ar weight of the sample, and on the pyrolysis temperature, can give sp ecific information about the mechanisms of initiation and temination i n chain degradation processes. (II) Direct comparisons of observed rat e constants for volatiles evolution can indicate whether all observed products are primary products. (III) Anomalous dependence of product y ields with decreasing sample thickness can give information about diff usion control of degradation rates. (IV) Anomalous dependence of produ ct yields and ratios which increases with increasing sample thickness can distinguish primary, secondary, and even tertiary products, and ca n moreover lead to the interpretation of the overall pyrolysis mechani sms in terms of a reaction scheme involving parallel and consecutive r eactions. All of the above are illustrated with examples from studies by the authors on a number of polymeric systems.