Hydrosilylation of allyl alcohol with [HSiMe2OSiO1.5]8:: Octa(3-hydroxypropyldimethylsiloxy)octasilsesquioxane and its octamethacrylate derivative as potential precursors to hybrid nanocomposites

Octakis(3-hydroxypropyldimethylsiloxy)octasilsesquioxane (OHPS) can be synthesized by direct hydrosilylation of allyl alcohol with octakis(dimethylsiloxy)octasilsesquioxan (HSiMe2O)Si8O12 (Q(8)M(8)(H)), using platinum divinyltetramethyldisiloxane [Pt(dvs)] as catalyst. Surprisingly, C-hydrosilylation occurs in preference to O-silylation. Hydrosilylation of trimethylsiloxy-2-propene with Q(8)M(8)(H), followed by desilylation also gives pure OHPS. OHPS reacts with methacryloyl chloride to give octakis(3-methacryloxypropyl-dimethylsiloxy)octasilsesquioxane (OMPS), a thermal and UV/vis curable precursor to organic/inorganic nanocomposites. Direct hydrosilylation of Q(8)M(8)(H) With 2-allyloxyethanol also proceeds primarily via C- rather than O-silylation. In contrast, compounds such as 1,3,5,7-tetramethylcyclotetrasiloxane (D-4(H)), 1,1,3,3-tetramethyldisiloxane (TMDS) or terminal Si-H functionalized poly(dimethylsiloxane) (PDMS-H, MW = 400), give significant amounts of O-silylation along with C-silylation. Initial catalyst concentration studies suggest that the catalytic cycle requires the intermediacy of Pt cluster complexes in contrast to recent studies on the mechanism of hydrosilylation which suggest monometallic complex catalysis.