The Preparation Of Silica/poly(tert-butyl Acrylate) Core/shell Composite Particles By Dispersion Polymerization

The aim to synthesize the composite particles based on silica as core and poly(tert-butyl acrylate) as shell in this work, is to prepare the inorganic/organic core/shell composite particles whose shells are composed of poly(acrylic acid) by transforming poly(tert-butyl acrylate) into poly(acrylic acid) by hydrolysis. Since the poly(acrylic acid) shells are pH-sensitive and can swell or shrink in response to environmental pH change, the particles are expected to be used as carriers for catalysts or enzymes, which activity can be controlled by environmental pH value.The colloidal silica particles which were synthesized by sol-gel process were firstly modified by 3-(trimethoxysilyl)propyl methacrylate (MPS) to graft C=C groups on their surface. The effect of the reaction time, MPS amount used and the reaction temperature on the MPS grafting amount on the silica surface was investigated. The grafting amount increased with increasing the reaction time and the MPS amount used, but it was less influenced by the reaction temperature.The dispersion polymerization behavior of tert-butylacrylate (tBA) was investigated based on ethanol/water mixing solvent as dispersion medium, polyvinylpyrrolidone (PVP) as stabilizer and azobisisobutyronitrile(AIBN) as initiator. The effect of dispersion medium composition and monomer, initiator and stabilizer amount used in the feed on the monomer conversion, the diameter of poly(tert-butylacrylate) microspheres formed and their distribution coefficient were examined. The better conditions of the dispersion polymerization of tert-butylacrylate in ethanol/water dispersion medium were as follows: the mass ratio of ethanol to water is 60/40, the mass percentage of tBA to the dispersion medium is 10%, the mass percentage of AIBN and PVP to the monomer are 1% and 20%, respectively, reaction temperature 70℃and reaction time 24h. Under these reaction conditions, the monomer conversion exceeded 90%, and the diameter of poly(tert-butylacrylate) microspheres formed and their distribution coefficient were 0.95μm and 0.048, respectively.Silica/poly(tert-butyl acrylate) core/shell composite paricles were prepared via dispersion polymerization method using the MPS-modified colloidal silica particles as seeds, tert-butyl acrylate as monomer, PVP as stabilizer and AIBN as initiator. It was found that the morphological structure of the composite paricles was greatly effected by the initial concentration of silica and the amount of the stabilizer used. Pure poly(tert-butyl acrylate) particles were easily formed when the initial concentration of silica was much low, but the particles with multi-core were produced in the case of high concentration of silica. The particles with multi-core were easily formed when the stabilizer amount used was low. The morphological structure of the core/shell composite paricles was confirmed by TEM, and their chemical composition with silica and poly(tert-butyl acrylate) were identified by NMR and FTIR.