Degradation mechanisms of poly (methyl acrylate)—II. The contribution of depropagation with intramolecular transfer

Abstract

A kinetic study of the thermal degradation of poly(methyl acrylate) (PMA) has been carried out using pyrolysis-gas chromatography (PY-GC). The experiments were performed using a thermocouple-controlled resistive filament pyrolyser, and involved the pyrolysis of 5 μg samples at 400 °C for a range of pyrolysis times. The aim was to test the hypothesis that the monomeric and oligomeric products detected are primary pyrolysis products formed in parallel first-order reactions. If this were exclusively the case then intramolecular transfer during depropagation would be responsible for the formation of all oligomer yields. An important prediction arising from the theoretical treatment of a set of parallel first-order reactions is that the rate constant for the growth of any product, expressed as a fraction of the limiting yield of that product, is the same for all products of the set. This can be used as a test for first-order parallel reactions. The results obtained in this work are not consistent with this test, and indicate that consecutive (secondary) reactions influence the product yields in the pyrolysis of PMA under the experimental conditions used in this study. On this basis it is concluded that intramolecular transfer mechanisms, though important, are not totally controlling oligomer formation.