Thermal and themoxidative degradation processes in poly(bisphenol a carbonate)

Abstract

Progress in the study of thermal and thermoxidative decomposition processes of poly(bisphenol a carbonate) (PC) was obtained by Matrix assisted laser description ionization time of flight (MALDI-TOF) and FAB mass spectroscopic techniques. PC samples were subjected to thermal degradation (under inert atmosphere) heating at 300, 350, 400 and 450 °C. The MALDI mass spectra of the pyrolysis residues obtained at 300 °C showed only a progressive reduction of the abundance of cyclic oligomers and an increase of the molar mass of the PC sample most likely due to post-condensation polymerisation reactions. At 350 °C the occurrence of an extensive hydrolysis reaction producing phenol groups was observed. PC chains terminated with phenol groups together with chains bearing phenyl and isopropenyl end groups were observed at 400 °C. Condensed aromatic compounds such as xanthones were also detected in the MALDI spectra of PC samples heated at 400 °C, and they became the most intense species at 450 °C. The FAB-MS spectrum of the pyrolysis residue obtained at 400 °C subjected to a selective and exhaustive aminolysis reaction showed the presence of compounds containing several consecutive xanthone units. These units undergo cross-linking processes, leading to a graphite-like charred residue (insoluble), as the temperature increases. The thermoxidative degradation of PC carried out heating the samples in air at 300 °C for 30, 60, 90, 120, 150 and 180 min produced a reduction of the PC molar mass. The MALDI mass spectra of thermally oxidised PC samples at 300 °C for 90 and 180 min showed the presence of PC chains terminated with methyl-ketone, phenyl and phenol groups, most likely formed by the oxidative degradation of the isopropilidene bridge of bisphenol A units. The presence of dehydrogenated structures containing biphenyl linkage may account for the insoluble residue produced in these conditions.