STUDY ON THERMAL-DEGRADATION OF POLYSTYRENES BY PYROLYSIS-GAS CHROMATOGRAPHY AND PYROLYSIS FIELD-IONIZATION MASS-SPECTROMETRY

The mechanism of the thermal degradation of polystyrene was studied by pyrolysis-gas chromatography and pyrolysis-field ionization mass spectrometry, using a block copolymer of ordinary and perdeuterated styrene [poly(styrene-b-styrene-d8)]. The main degradation products were monomers, dimers and trimers of the styrenes. Quite large amounts of hybrid dimers of styrene and styrene-d8 units were formed as well as the homo-dimers of the two types of units in the block copolymer, whereas formation of hybrid trimers was negligible. The principal hybrid dimers were CD2C(C6D5)CD2CH2(C6H5) and CH2C(C6H5)CH2CD2(C6D5), and their yields were comparable with those of the homo-dimers. These results suggest that the dimers are primarily formed through the reactions of unsaturated chain-ends and benzyl radicals which are generated by 1,5-transfer of the secondary macroradical followed by β-scission. On the other hand, dimer formation through 1,3-transfer, as proposed by many authors, was confirmed not to be the main pathway to the dimers. © 1990.