Abstract: The liquid crystalline properties of side-chain copolysiloxanes containing 4-methoxyphenyl benzoate mesogens and azobenzene photochromic groups were characterized by polarized microscopy with a hot stage(POM)and DSC.On incorporation of nonmesogenic units into polysiloxane PS Ⅱ-1 the type of mesophase did not chang for copolymers PS Ⅱ-2 and PS Ⅱ-3, but smectic texture is only preserved for copolymer PS Ⅱ-4.The mole fraction limit of mesogenic units needed for mesophase existence of copolysiloxanes of mesogenic monomers with monomers, which do not contain mesogenic fragments, is to be 80 mol%;In the composition region of mesophase existence the lowering of melting temperature is accompanied by the increasing of nonmesogenic component content of copolymers and their isotropic temperature, enthalpy and entropy pass through a minimum at 10 mol%of nonmesogenic units of PS Ⅱ-3, as shown in Fig, 3.

Key words: Thermotropic liquid crystalline polymers, Side-chain copolysiloxanes, 4-Methoxyphenyl benzoate, Smectic phase