The FTIR-Raman spectra of polydiacetylenes with chiral pendent groups (-(CH2)(n)(OCoNHCH)-H-x(CH3)Ph; n = 2,3,4,6 and 9; nR(S)MBU) were measured for samples as polymerised, cast from solution and precipitated on filter paper. Peaks due to the -C = C- and -C = C-backbone stretching vibrations occur above 1400 cm(-1). A series of peaks due to the interaction of backbone and -(CH2)(n)- vibrations, which reflect the structure of the alkyl chains in the pendent groups, lie between 700 and 1400 cm(-1). Comparison with the spectra of the related n-butoxy-carbonylmethylurethane sidegroup polymers (nBCMU) shows that, with the exception of 9R(S)MBU polymers, the alkyl chains of the nR(S)MBU polymers do not adopt a single conformation even in the as-polymerised samples. This is a consequence of the steric hindrance of the bulky chiral unit at the end of the pendent groups.