Pyrolysis-mass spectrometric investigations of the mechanistic and kinetic aspects of thermal degradation of phenol-formaldehyde polycondensates

High-molecular-weight phenol-formaldehyde polycondensates, deuterium-labelled at the aromatic or methylene linkages, were subjected to pyrolysis in the direct insertion probe of a mass spectrometer or in separate pulse-mode pyrolysers interfaced to the mass spectrometer or to the gas chromatograph-mass spectrometer. The principal route of the thermal degradation in vacuum and in an inert atmosphere,involving the cleavage of phenol-methylene bonds and subsequent hydrogen abstraction and resulting in the ultimate formation of phenol and methyl-substituted phenols as volatile products, exhibited hydrogen-deuterium scrambling owing to the isomerization of themacroradicals. The degree of scrambling was found to be dependent on the pyrolysis conditions (temperature, rate of temperature rise). At higher temperatures, hydrogen abstraction is kinetically favoured over the scission of benzyl bonds.