Degradation mechanisms of poly(methyl acrylate) — III. An assessment of the participation of secondary reactions from the dependence of pyrolysis yields on sample thickness

Abstract

The thermal degradation of poly(methyl acrylate) (PMA) was studied using pyrolysis gas chromatography (py-gc) with a thermocouple-controlled resistive filament. Samples of different thicknesses were pyrolysed at 500 °C for 10 s. Under these conditions only partial pyrolysis of the samples resulted. Product yields were measured as a function of sample thickness, for samples in the 1–10 μg range. The residence times of the products in the polymer melt varied with sample thickness, and this allowed possible secondary reactions to be detected. From the quantitative results of the bonus and deficit yields it is shown that as sample size increases, monomer and trimer are produced in excess 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 dimeric species was also produced exclusively by secondary reactions, since it was not detected unless the sample thickness exceeded a certain value. Possible degradation mechanisms have been proposed from this sample size study.