PYROLYSIS FIELD-IONIZATION MASS-SPECTROMETRY OF POLYOLEFINS

This report describes the pyrolysis field ionization mass spectrometric (Py-FI-MS) analysis of five polyolefins: polyethylene, polypropylene, poly(1-butene), poly(4-methyl-1-pentene), and polyisobutylene. Volatile pyrolyzates were typically observed at most or all carbon numbers to masses well above 1000 Daltons (Da). The distributions of pyrolyzates showed some similarities beteen the various polymers. Free radical degradation mechanisms have been proposed to explain the patterns of volatile pyrolyzates. These mechanisms are characterized by three principal reaction types: (a) main-chain cleavage to form chain-terminus radicals; (b) intramolecular radical transfer (backbiting) to form internal radicals; (c) beta-scission to form both volatile products and terminally unsaturated polymer residues. All five polymers yielded only one major series of oligomers at lower masses (up to 600 Da or so); these are 1-alkene pyrolyzates. At higher masses (up to 1600 Da or so), most of the polymers yielded intense dialkene volatile pyrolyzates. These results suggest that other hydrocarbon polymers, including copolymers, might also be analyzed successfully by Py-FI-MS.