SURFACE FUNCTIONALIZED COLLOIDAL SILICA PARTICLES FROM AN INVERSE MICROEMULSION SOL-GEL PROCESS

Colloidal silica particles are prepared via a sol gel technique carrie d out in an inverse microemulsion of water in a toluene solution of te traethoxysilane (TEOS), stabilized by either an anionic surfactant AOT or isopropanol. Functionalized material was obtained using a function al coupling agent (RO)(3)Si(CH2)(3)X, X being a functional group such as methacryloyl, thiol, vinyl, amino group, or a chlorine atom. Functi onalization can be carried out either directly via the direct copolyco ndensation of TEOS and the coupling agent, or in a two-step process in volving a core-shell polycondensation of the coupling agent onto prefo rmed silica particles. Kinetic studies of the copolycondensation are c arried out using either Si-29 NMR analysis or liquid chromatography. T hey show that the consumption of TEOS is more rapid than that of the c oupling agent. The materials are characterized both chemically (elemen tal analysis, FTIR, C-13 and Si-29 NMR CPMAS analysis), and by their p article size. The silica functionalized with a polymerizable methacryl oyl group is encapsulated by a polymer layer in an inverse emulsion po lymerization of acrylic acid. After inversion of the emulsion in water , the resulting material is covered with a layer of hydrophobic polyme r in a conventional emulsion polymerization.