Rheological properties of liquid-crystalline side-group polymers in the isotropic, nematic, and smectic states

The melt viscosity of seven liquid-crystalline side-group polymers with polyacrylate and polysiloxane main chains is measured as a function of shear rate and temperature. In the isotropic and also in the nematic phase none or only a very small dependence of the melt viscosity on shear rate is observed for the shear rates investigated. The melt viscosity in the nematic phase is higher than that in the isotropic phase. This is contrary to the results for liquid crystalline mainchain polymers and points to the fact, that there is no resulting orientation in shear flow of liquid-crystalline side-group polymers in the nematic phase. In the smectic phase the melt viscosity is very high and strongly shear-rate dependent. These results are compared with dielectric relaxation measurements on polymethacrylates and a polychloroacrylate.