Frank elastic constants and rotational viscosity for nematic solutions of main-chain polymers

Studying dilute solutions of a main-chain mesomorphic polymer in a conventional nematic liquid crystal, we have measured the splay and bend elastic constants, as well as the rotational viscosity coefficient in those systems. We observed that both static and dynamic properties are significantly affected by the addition of even a small quantity of polymer. The large increment of the rotational viscosity coefficient may be explained in the framework of a model of anisotropic dumbell, due to F. Brochard. These viscoelastic effects are compared to analogous measurements obtained in the case of solutions of side-chain polymers. The general conclusion we deduce is that the main-chain polymer we study, although exhibiting a significant anisotropy as for its conformation, does not look like a stretched chain, but is largely swollen in three dimensions.