Synthesis and Thermal and Phase Behavior of Polysiloxanes with Grafted Dialkyl-Substituted [1]Benzothieno[3,2-b][1]benzothiophene Groups

number of novel polysiloxanes with grafted dialkyl-substituted [1]benzothieno[3,2-b][1]ben-zothiophene groups is synthesized by the hydrosilylation of polymethylsiloxane matrices with varying ratio of functional methylsiloxane and nonfunctional dimethylsiloxane fragments (1 : 5, 1 : 1, and 1 : 0) by reactive 2-undecenyl-7-hexyl-[1]benzothieno[3,2-b][1]benzothiophene. The obtained comb-shaped polymers have a number-average molecular weight of (6-43) x 10(3) and a dispersity of 1.55-2.79. Study of the thermal and thermo-oxidative properties shows that the polymer, in which each second monomer unit contains [1]ben-zothieno[3,2-b][1]benzothiophene substituents, has the highest thermo-oxidative stability (413 degrees?) and the smallest char residue at 700 degrees? (3%). The lowest thermal stability is exhibited by the comb-shaped polymer with the 100% content of [1]benzothieno[3,2-b][1]benzothiophene fragments and the highest molecular weight for which a 5% weight loss starts at 274 degrees?. The DSC study of the phase behavior of the synthesized polymers indicates that increase in the fraction of [1]benzothieno[3,2-b][1]benzothiophene fragments in monomer units and their molecular weight contributes to a rise in phase transition temperatures and reduc-tion in their enthalpy compared with the monomer and the siloxane dimer of [1]benzothieno[3,2-b][1]ben-zothiophene. Introduction of 50 and 100% of [1]benzothieno[3,2-b][1]benzothiophene fragments into the siloxane polymer chain leads to the formation of liquid-crystalline mesophases with the enthalpy of transi-tions typical of smectics, as evidenced by polarizing microscopy and X-ray diffraction. For the polymers with the varied content of [1]benzothieno[3,2-b][1]benzothiophene fragments the values of the interlayer spacing in the smectic mesophase are determined, and their phase behavior is investigated. Effect of molecular weight on the packing of [1]benzothieno[3,2-b][1]benzothiophene is ascertained, and models for the interpenetra-tion of side substituents in the obtained polymers are constructed.