DEGRADATION MECHANISMS OF POLY(METHYL ACRYLATE) - III - AN ASSESSMENTOF THE PARTICIPATION OF SECONDARY REACTIONS FROM THE DEPENDENCE OF PYROLYSIS YIELDS ON SAMPLE THICKNESS

The thermal degradation of poly(methyl acrylate) (PMA) was studied usi ng pyrolysis gas chromatography (py-gc) with a thermocouple-controlled resistive filament. Samples of different thicknesses were pyrolysed a t 500 degrees C for 10 s. Under these conditions only partial pyrolysi s of the samples resulted. Product yields were measured as a function of sample thickness, for samples in the 1-10 mu g range. The residence times of the products in the polymer melt varied with sample thicknes s, and this allowed possible secondary reactions to be detected. From the quantitative results of the bonus and deficit yields it is shown t hat as sample size increases, monomer and trimer are produced in exces s of the yield corresponding to primary reactions. On the other hand, observed higher oligomers are produced in lower than expected yields. This suggests the occurrence of secondary (consecutive) reactions. A d imeric species was also produced exclusively by secondary reactions, s ince it was not detected unless the sample thickness exceeded a certai n value. Possible degradation mechanisms have been proposed from this sample size study. (C) 1997 Elsevier Science Limited.