DEGRADATION MECHANISMS OF POLY(METHYL ACRYLATE) .2. THE CONTRIBUTION OF DEPROPAGATION WITH INTRAMOLECULAR TRANSFER

A kinetic study of the thermal degradation of poly(methyl acrylate) (P MA) has been carried out using pyrolysis-gas chromatography (PY-GC). T he experiments were performed using a thermocouple-controlled resistiv e filament pyrolyser, and involved the pyrolysis of 5 mu g samples at 400 degrees C for a range of pyrolysis times. The aim was to test the hypothesis that the monomeric and oligomeric products detected are pri mary pyrolysis products formed in parallel first-order reactions. If t his were exclusively the case then intramolecular transfer during depr opagation would be responsible for the formation of all oligomer yield s. An important prediction arising from the theoretical treatment of a set of parallel fist-order reactions is that the rate constant for th e 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 obtain ed in this work are not consistent with this test, and indicate that c onsecutive (secondary) reactions influence the product yields in the p yrolysis 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. (C) 1997 Elsevier Science Limited.