Two new types of silsesquioxanes, (HSiO 3/2 ) x [( t BuO)SiO 3/2 ] z or T H Q and (HSiO 3/2 ) x (RSiO 3/2 ) y [( t BuO)SiO 3/2 ] z or T H T R Q (R ) octadecyl), were synthesized and studied as low-k dielectric materials for electronic applications. The materials were prepared by cohydrolysis and condensation of alkoxy monomers, (AcO) 2 Si(O t Bu) 2 , HSi(OEt) 3 , and CH 3 (CH 2 ) 17 Si(OMe) 3 . Spectroscopic data supported retention of tertiary alkoxy groups [( t BuO)SiO 3/2 or ( t BuO) 2 SiO 2/2 ] and presence of silanol. The molecular weight of (HSiO 3/2 ) x [( t BuO)SiO 3/2 ] z increased with the T/Q ratio, while that for (HSiO 3/2 ) x (RSiO 3/2 ) y [( t BuO)SiO 3/2 ] z exhibited less dependence on composition. The tert butoxy groups were eliminated in both materials at low temperatures (<450 °C), and subsequent decomposition of octadecyl group (R) in (HSiO 3/2 ) x (RSiO 3/2 ) y -[( t BuO)SiO 3/2 ] z occurred through cleavage and re-distribution of carbon-carbon bonds (430-550 °C). Heating at 450 °C for 2 h afforded porous solids. The total pore volume of materials derived from (HSiO 3/2 ) x [( t BuO)SiO 3/2 ] z determined by nitrogen sorption porosimetry increased with increasing Q content up to 0.313 cm 3 /g or 38% porosity by volume. The porosity for (HSiO 3/2 ) x (RSiO 3/2 ) y [( t BuO)SiO 3/2 ] z ranged from 32 to 54% (0.349-0.701 cm 3 /g), which represented an ∼10% increase over (HSiO 3/2 ) x [( t BuO)SiO 3/2 ] z . Thin films prepared from (HSiO 3/2 ) x [( t BuO)SiO 3/2 ] z exhibited a modulus between 10 and 19 GPa, but had a high dielectric constant due to residual silanol. Incorporation of RSiO 3/2 group allowed for formation of porous materials with low silanol contents. The dielectric constant and modulus of (HSiO 3/2 ) x (RSiO 3/2 ) y -[( t BuO)SiO 3/2 ] z were in the range of 1.7-2.6 and 1.8-4.7 GPa, respectively.

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The design, synthesis, and properties of two new types of poly(borosiloxane) preceramic polymers, diethylborazine- (PVS−DEB) and pinacolborane-modified (PVS−PIN) poly(vinylsiloxane)s, are reported. The polymers are synthesized in excellent yields by the RhH(CO)(PPh3)3-catalyzed reactions of poly(vinylsiloxane) (PVS) with either diethylborazine (DEB−H) or pinacolborane (PIN−H). The spectroscopic data for the polymers, along with results of the RhH(CO)(PPh3)3-catalyzed hydroboration reactions of diethylborazine and pinacolborane with the model compound vinyltris(trimethylsiloxy)silane, are consistent with predominately anti-Markovnikov hydroboration of the polymer vinyl groups by the boranes. The degree of polymer hydroboration is simply controlled by varying the reactant ratios with the compositions of the PVS−DEB polymer ranging from (MeSiO1.5)0.42(PhSiO1.5)0.37(ViMe2SiO0.5)0.17(DEB(CH2)2Me2SiO0 .5)0.04 to (MeSiO1.5)0.42(PhSiO1.5)0.37(DEB(CH2)2Me2SiO0.5)0.21 and those of the PVS−PIN polymers from (MeSiO1.5)0.42(PhSiO1.5)0.37(ViMe2SiO0.5)0.18(PIN(CH2)2Me2SiO0. 5)0.03 to (MeSiO1.5)0.42(PhSiO1.5)0.37(PIN(CH2)2Me2SiO0.5)0.21. The borane-modified polymers are soluble and stable in ethers, acetone, methylene chloride, benzene, and pentane. Molecular weight analyses using SEC with refractive index, viscometry, and light-scattering triple detection show significant differences in hydrodynamic volume, molecular weight, radius of gyration, and conformation, which indicate that the PVS−PIN and PVS−DEB polymers adopt a more branched and spherical structure compared to the unmodified PVS. Bulk pyrolysis of the modified resins produced SiOCB ceramic chars with boron contents ranging from 0.3 to 0.7% depending upon the percentage of polymer modification. XRD and TEM studies of the 1800 °C chars of PVS and PVS−PIN showed significant differences in the degree of grain growth and distribution with the boron-modified char showing both a smaller average crystallite size and a more narrow size range. The PVS−PIN polymers were found to be excellent melt-processable, single-source precursors to small-diameter SiOCB fibers.