X-ray scattering experiments on oriented polysiloxanes with paired mesogens and different distances between these swallow-tailed side groups show a remarkable dependence of the smectic monolayer thickness on the degree of dilution, whereas the interplanar distances of the side groups remain nearly constant. Due to the dominating interaction of the mesogenic moieties, the flexible main chain is forced to take part in the layer formation. A packing model is proposed to explain the results of the X-ray studies. For polymers with five or more dimethylsiloxane copolymer segments, a diffuse scattering appears in the smectic as well as in the isotropic phase. This scattering is independent of the orientation of the samples. It is probably caused by the main chain and has also been observed for the unsubstituted poly(hydrogenmethylsiloxane).

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