| Abstract: | Flexible linear polysiloxanes with inorganic backbones such as poly(diethylsiloxane) and poly-(dipropylsiloxane) contain no traditional mesogenic groups neither in the main chain nor in side chains and, nevertheless, they are able to form thermotropic mesophases. Recent developments in the study of thermodynamics, kinetics, structure and morphology of these mesophase polymers are considered. The temperature interval of existence of the mesophase is strongly dependent on the length of side radicals and molecular weight. These dependences are examined in detail. X-ray structure and the optical textures seen in the polarizing microscope are discussed. It is shown that large mesophase lamellae represent a very characteristic feature of the morphology of poly(diethylsiloxane). The linear growth rate of the lamellae and the overall calorimetric kinetics of the mesophase formation have been studied at various temperatures and the results obtained have been analyzed using the Avrami equation and the kinetic theory of the linear growth. As a result of the kinetic analysis two-dimensional growth has been suggested in accordance with the microscopic observation. The formation of the mesophase in slightly crosslinked poly(diethylsiloxane) samples can be initiated by stretching. The stress-strain and thermomechanic (deformation calorimetry data) behaviour of such samples is briefly discussed. |
