Synthesis, Characterization and Microstructure of New Liquid Poly(methylhydrosiloxanes) Containing Branching Units SiO4/2.

Six liquid branched poly(methylhydrosiloxanes) of new random structures (PMHS-Q), containing quadruple branching units SiO4/2 (Q), both MeHSiO (DH) and Me₂SiO (D) chain building units (or only mers MeHSiO), and terminal groups Me₃SiO0.5 (M) were prepared by a hydrolytic polycondensation method of appropriate organic chlorosilanes and tetraethyl ortosilicate (TEOS), in diethyl ether medium at temperature below 0 °C. Volatile low molecular weight siloxanes were removed by a vacuum distillation at 150⁻155 °C. Yields of PMHS-Q reached from 55⁻69 wt%. Their dynamic viscosities were measured in the Brookfield HBDV+IIcP cone-plate viscometer and ranged from 10.7⁻13.1 cP. Molecular weights (MW) of PMHS-Q (Mn = 2440⁻6310 g/mol, Mw = 5750⁻10,350 g/mol) and polydispersities of MW (Mw/Mn = 2.0⁻2.8) were determined by a size exclusion chromatography (SEC). All polymers were characterized by FTIR, ¹H- and 29Si-NMR, and an elemental analysis. A microstructure of siloxane chains was proposed on a basis of 29Si-NMR results and compared with literature data.