Primary thermal degradation processes of poly(ether-sulfone) and poly(phenylene oxide) investigated by direct pyrolysis-mass spectrometry

The thermal degradation processes which occur in poly(ether-sulfone) (PES) and poly(phenylene oxide) (PPO) have been studied by Direct Pyrolysis-Mass Spectrometry (DPMS). The pyrolysis mass spectra of PES and PPO contain molecular ions up to m/z 700, corresponding to pyrolysis compounds of sufficient size to allow the characterization of the primary processes which occur in the thermal cleavage of these polymers. The results obtained indicate that the thermal degradation of PES and PPO proceeds by thermal cleavage of the groups located at the bridges. In the case of PPO the bridges are all homogeneous, and therefore both an intramolecular thermal rearrangement or a radical cleavage process can account for the formation of the primary pyrolysis products. Formation of dibenzofuran units along the PPO chain is a parallel thermal process. In the case PES the simultaneous thermal cleavage of two different bridged units, diphenyl sulfone and diphenyl ether occurs. Extrusion of SO₂, with consequent formation of compounds containing biphenyl units, is observed in the thermal degradation of PES. This process is accompanied by formation of dibenzofuran units along the polymer chain, as expected from the thermal cleavage of diphenyl ether units, and by another rearrangement of the polymer backbone, yielding structures containing more oxygen atoms with respect to that of PES.