GC–MS correlation of C3n series of naturally occurring highly branched alkanes and polypropylene oligomers

Several series of polypropylene (PP) oligomers and monounsaturated analogues extended by (+C3) 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 C3n sequences of highly branched alkanes (HBAs) recently detected in a few different environmental settings. By establishing that the structure of the C3n 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 ω5 and with additional methyl groups at 6, 8, 10, etc. for ⩾C15 members best fits the current data. Whilst a common industrial chemical is identified here as one source of the C3n HBA series, their environmental occurrences are coincident with lithological and molecular features suggestive of a bacterial source.