Structure of ordered phases in hexylphenylsiloxane copolymers

The temperature evolution of the phase state and the structure of ordered phases in linear poly(hexylphenylsiloxanes) {[Ph 2 SiO] m [HexPhSiO]} p with m = 2, 3, and 5 were studied by the methods of DSC and X-ray analysis. This complex study made it possible to identify phase transitions and to assess temperature intervals of the existence of such ordered phases. It was shown that polymers with m = 3 and 5 are able to produce one crystalline and two mesomorphic phases in different temperature intervals. Throughout the temperature region below the isotropization point, a polymer with m = 2 exists in the mesomorphic phase; at T g , this polymer is transformed into a mesomorphic glass. An analysis of X-ray characteristics allows structural identification of crystalline and mesomorphic modifications. Crystal cells of polymers with m = 3 and 5 are shown to be orthorhombic (symmetry Pbn2 1 ) with the parameters a = 21.30 and 21.05 A, h = 10.39, 10.34 A, and c = 5.12 and 5.10 A. Orthorhombic cells involve two polymer chains, and each cell contains four monomer units. The low-temperature mesophase of crystallizable polymers and the high-temperature mesophase formed in all the three polymers under study belong to columnar mesophases Col ho and Col hd , respectively.