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 temperatures can be solved by appropriate filament design and the use of sufficiently 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) Dependence of rate constants for volatiles evolution on the initial molecular weight of the sample, and on the pyrolysis temperature, can give specific information about the mechanisms of initiation and temination in chain degradation processes. (II) Direct comparisons of observed rate constants for volatiles evolution can indicate whether all observed products are primary products. (III) Anomalous dependence of product yields with decreasing sample thickness can give information about diffusion control of degradation rates. (IV) Anomalous dependence of product yields and ratios which increases with increasing sample thickness can distinguish primary, secondary, and even tertiary products, and can moreover lead to the interpretation of the overall pyrolysis mechanisms in terms of a reaction scheme involving parallel and consecutive reactions. All of the above are illustrated with examples from studies by the authors on a number of polymeric systems.