Branched functionalised polysiloxane–silica hybrids for immobilisation of catalysts

Abstract

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.