We report on the first x-ray scattering measurements of pretransitional smectic-C fluctuations in the nematic phase of a side-chain polymeric liquid crystal, C-6 polysiloxane. The data are well described by the mean-field theory of Chen and Lubensky suggesting that the mesogenic side groups are only weakly coupled to the polymeric backbone. Because of disorder in the polymer backbone, the correlation lengths, in the vicinity of the nematic-smectic-C phase transition, are weak functions of temperature and their magnitudes are smaller than those of conventional monomeric liquid crystals
