MALDI-TOF investigation of polymer degradation. Pyrolysis of poly(bisphenol A carbonate)

The MALDI-TOF technique allows the detection of intact polymer molecules up to high masses and therefore offers the opportunity to study directly the thermal degradation processes occurring in polymeric materials by analyzing conveniently exposed (i.e., partially degraded) polymer samples. This opens new vistas in polymer analysis and deserves careful exploration, due to the relevance of polymer degradation phenomena in everyday practice. The thermal decomposition of poly(bisphenol A carbonate) (PC) has been investigated by heating isothermally at 300, 350, 400, and 450 degrees C and subsequent analysis of the pyrolysis residue by means of MALDI mass spectrometry. The MALDI mass spectra of the pyrolysis residues obtained at 300 degrees C showed a progressive reduction of the abundance of cyclic oligomers, whereas the relative abundance of the other compounds was unaffected. At 350 degrees C, the occurrence of an extensive hydrolysis reaction was responsible for the degradation of cycles and linear chains bearing tert-butylphenyl carbonate end groups with subsequent formation of abundant open chain PC oligomers with phenol end groups. Furthermore, at these two temperatures, cyclic oligomers never disappear in the MALDI spectra, even at higher heating time (60 min), suggesting the presence of an equilibrium between the rate of cleavage and the rate of formation of cycles. PC chains terminated with phenol groups at both ends, together with pyrolyzed chains bearing phenyl and isopropylidene end groups, generated by the disproportionation of the aliphatic bridge of bisphenol A, were observed in the MALDI spectra of pyrolysis residue obtained at 400 degrees C. Condensed aromatic compounds such as xanthones, which are considered to be the precursors of a graphite-like structure of the charred residue, were also detected in the MALDI spectra of PC samples heated at 400 degrees C and they became the most intense species at 450 degrees C. The PC samples heated at temperature higher than 450 degrees C consisted of insoluble carbonaceous materials not suitable for MALDI analysis.