Résumé
We have studied some static and dynamic properties of side-chain nematic polymers. These materials, newly synthetized, are constituted by a polymeric main chain grafted with mesomorphic moieties. They thus combine specific features of polymeric compounds as well as typically nematic anisotropic properties. In a first part, we have measured the elastic constants and the twist viscosity of those polymers. The main results are: - the order of magnitude of the elastic constants is close to those of conventional nematic medium;- the twist viscosity coefficient, on the contrary, is several orders of magnitude larger than in low molar weight compounds. Moreover, it may be interpreted in the frame of the standard free volume theory on polymers. Indirectly, we deduce from these measurements that the polymeric back¬bone takes an anisotropic shape and that the rotation of the director involves a cooperative notion of the main chain. The coupling between the two parts of this composite abject is then evidenced both in the static and dynamic properties. In a second part, v.>e have studied the transport properties of these polymers. Using the forced Rayleigh scattering experiment, we compare the diffusion constants in two perpendicular directions in the polymers and in a chemically similar conventional liquid crystal. We find, for the same probe, that the order of magnitude of the diffusion coefficients in much smaller for polymers than for liquid crystals. Moreover, the anisotropy of diffusion regarding to the director orientation, is inverted between the two types of compounds. We conclude that the presence of the backbone modifies, at least at a local scale, the symmetry of the nematic medium.