GC–MS correlation of C 3 n series of naturally occurring highly branched alkanes and polypropylene oligomers

Abstract

Several series of polypropylene (PP) oligomers and monounsaturated analogues extended by (+C 3) PP monomer addition have been detected in the solvent extractable fraction and the pyrolysate of a commercially available PP. On the basis of identical gas chromatography–mass spectrometry (GC–MS) data, two of the PP oligomer series are assigned as the two unusual C 3 n sequences of highly branched alkanes (HBAs) recently detected in a few different environmental settings. By establishing that the structure of the C 3 n HBAs exclusively contains methyl branching and is extended by PP monomer units, the mass spectra of these compounds can be interpreted with greater intuition. Several branched alkane structures, which may provide a good representation of the mass spectra, are proposed. Of these, a structural series containing methyl groups at the carbon backbone positions 2, 3 and ω 5 and with additional methyl groups at 6 , 8 , 10 , etc. for ⩾C 15 members best fits the current data. Whilst a common industrial chemical is identified here as one source of the C 3 n HBA series, their environmental occurrences are coincident with lithological and molecular features suggestive of a bacterial source.