Thermal degradation mechanisms of poly[diethyl 2-(methacryloyloxy)ethyl phosphate] by Py-GC/MS

Thermal decomposition properties of poly[diethyl 2-(methacryloyloxy)ethylphosphate] (PDMP) were studied using a stepwise pyrolysis-gas chromatography/mass spectrometry (stepwise Py-GC/MS) method. The individual mass chromatograms of the various pyrolysates were correlated with the pyrolysis temperature in order to elucidate the degradation mechanisms. The scission of PDMP in helium atmosphere showed the presence of two-stage pyrolysis regions. Triethylphosphate reached maximum evolution at the initial pyrolysis temperature, indicating that scisson of PDMP was initiated by the selective cleavage at the chain end and phosphate ester side chain as the dominant pyrolysis mechanism in the first stage. This local instability at chain end and phosphate ester side chain might explain the thermal instability of PDMP at lower pyrolysis temperatures. Acetaldehyde and water, as major products, were formed in significant amounts above 300 °C, indicating that random chain scission became the dominant pyrolysis mechanism in the second stage. Thus, the random chain scission reaction favored the occurrence of crosslinking and cyclization through chain transfer of carbonization catalyzed by phosphate ester along with the evolution of the arylene-containing and cyclic compounds. From mechanism analysis of PDMP pyrolysis, the introduction of a chemically bonded phosphorous-containing pendant group could promote its fire retardancy to form the high char yield of solid residue.