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On the longitudinal acoustic mode in branched and unsaturated polyethylenes

Hans Lewandowski, Robert J.Meier

The Raman vibrational spectra of branched alkanes and alkenes were studied by quantum calculations in order to investigate the effect of branching and unsaturation on the main chain LAM mode in polyethylenes. It was found that alkyl side chains have a minor effect on themain chain LAMmode. On the contrary, non-terminal unsaturations within the main chain do have a significant effect on the LAM-1 mode. It is shown that former interpretation of the spectra of LAM bands in non-terminally unsaturated C18H26 requires a different, renewed, description.