M. Ścibiorek

Branched functionalised polysiloxane–silica hybrids for immobilisation of catalysts

Silica hybrids of functionalised polysiloxanes of well-defined structures, having various topologies (linear, comb-branched and dendritic-branched) and various densities of functional groups, were prepared. These hybrids were generated by the grafting of the polysiloxane to the prefunctionalised surface of porous silica particles. Polymers were obtained by living anionic ring opening polymerisation initiated by BuLi in THF of 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, V3, 2-(diphenylphosphino)ethyl-2,4,4,6,6-pentamethylcyclotrisiloxane, PD2, and by copolymerisations of V3 with hexamethylcyclotrisiloxane, D3 and with 2-vinyl-2,4,4,6,6-pentamethylcyclotrisiloxane, VD2. Living polysiloxanes were terminated on the –CH2CH2SiMe2Cl groups present on the modified silica surface. Vinyl groups, besides being the destination for the immobilisation of the metalloorganic catalyst, were also the precursors for the generation of –CH2CH2SiMe2Cl groups used for the grafting of living polysiloxanes to build comb-branched and dendritic-branched polymers on the hybrid structures. Dendritic and comb polysiloxanes were also synthesised separately and were then attached to the silica particle surface functionalised with –CH2CH2SiMe2OSiMe2H groups. A Pt(II) complex was attached to the vinyl groups of the hybrids. A high catalytic activity of this complex was found in the test reaction of hydrosilylation of 1-hexene by PhMe2SiH.

Synthesis and some properties of polyoxyhexakis (dimethylsilylene) and its copolymers with dimethylsiloxane

The synthesis of polyoxyhexakis(dimethylsilylene).1. by the hydrolytic polycondensation of α,ω-dichlorohexakisdimethylsilylene,2. and by cationic ring-opening polymerization of dodecamethyloxahexasilacycloheptane.6Dj, initiated with a protic acid is reported. The possibility of synthesis of alternative copolymers composed of oxyhexakis(dimethylsilylene) units and dimethylsiloxane or oligodimethylsiloxane units were also explored. Polymers are characterized by NMR spectroscopy. Their thermal behavior is discussed.

Polysiloxane–silica hybrids from novel precursors by the sol–gel process

1,1,1,7-Tetramethoxy-3,3,5,5,7,7-hexamethyl-1,3,5,7-tetrasiloxane {TMOS-D3} and 1,1,1,7-tetramethoxy-3,5,7-trimethyl-3,5,7-trivinyl-1,3,5,7-tetrasiloxane {TMOS-V3} were made, respectively, by cationic telomerisation of hexamethylcyclotrisiloxane (D3) or 2,4,6-trimethyl-2,4,6-trivinylcyclotrisiloxane (V3) with tetramethoxysilane (TMOS). These compounds were used as precursors of siloxane–silica materials. Their structure resulted in the generation of short trisiloxane segments which were well dispersed in the formed hybrid framework. These precursors or their mixtures with TMOS were subjected to sol–gel polycondensation in dispersions or in bulk catalysed by NaOH. Siloxane–silica hybrid materials were obtained either in the form of precipitated particles (1–80 µm) of various regular or irregular shapes or in the form of a monolithic material disintegrated on drying. In the sol–gel dispersion process, which was performed in the presence of a surfactant, cetyltrimethylammonium bromide, almost all methyl groups were converted to oxygen bridging two silicon atoms while in the bulk process a small fraction of unreacted alkoxyl and hydroxyl groups remained in the gel. Materials obtained from pure {TMOS-D3} and {TMOS-V3} showed a very low porosity and surface area. In contrast, particles having a high surface area can be obtained from mixtures of these new precursors and TMOS. Gels prepared from {TMOS-V3} and its mixture with TMOS were subjected to hydrosilylation with HMe2SiCl and the silylated particles were used for grafting of a living polysiloxane polymer.