The Preparation And Characterization Of Core/Shell Composite Microparticles Based On Silica As Core And Poly(Tert-butylmethacrylate) As Shell

The aim to synthesize the composite microparticles based on silica as core and crosslinked poly(tert-butylmethacrylate) as shell in this work, is to prepare the inorganic/organic core/shell composite microparticles whose shells are composed of crosslinked poly(methacrylic acid) by transforming poly(tert-butylmethacrylate) into poly(methacrylic acid) by hydrolysis. Since the crosslinked poly(methacrylic acid) shells are pH-sensitive and can swell or shrink in response to the environmental pH change, the microrparticles are expected to used as carriers for catalysts or enzymes, which activity can be controlled by environmental pH value.Silica colloid particles were firstly synthesized by two different sol-gel processes. By means of batch sol-gel process, three kinds of silica colloid particles with different particle sizes were prepared by changing the water amount in the reaction feed. The spherical shape of the silicacolloid partices was observed by TEM or SEM, and as their particle sizes increased, their shape became more and more spherical and their monodispersity was improved. In the semi-batch sol-gel process, monodisperse silica colloid particles of different particle size were prepared by changing the feed times under maintaining constant number of silica seeds. The silica particle size increased from 120 nm to 550 nm within 4 hours in the semi-batch prcess, and the particle growth rate was much higher than that in the batch process.Then the silica colloid particles were modified by 3-(trimethoxysilyl)propyl methacrylate (MPS) to graft C=C groups on their surfaces. The MPS-modified silica colloid particles were characterized by elemental analysis, contact angle, FTIR, 29Si NMR and 13C NMR spectroscopy;and the results showed that the C=C groups were successfully grafted on the surface of the silica colloid particles. The mechanism of grafting of MPS on the surface of the silica particles may be as follows: MPS was firstly hydrolyzed, and the hydrolysis substance was polymerized by condensation reaction to form the oligomers;these oligomers were adsorbed on the surface of silica particles by hydrogen bonding, and then the linkage between the oligomers and the particles occurred by the condensation reaction between the hydroxyl of the oligomers and the hydroxyl on the surface of the silica particles.Silica/crosslinked poly(tert-butylmethacrylate) core/shell composite microparticles were prepared via seed emulsion polymerization method using the MPS-modified silica colloid particles as seeds, SDS as emulsifier, tert-butylmethacrylate as monomer and ethyleneglycol dimethacrylate as crosslinker. It was evidenced by the investigation of the effect of the factors on the morphological structure of the composite microparticles that, the formation of pure poly(tert-butylmethacrylate) colloid particles in the process of see-emulsion polymerization could be avoided by controlling the solid content of the silica seed emulsion;pure poly(tert-butylmethacrylate) colloid particles were tended to be formed under large amount of SDS used, while the core/shell composite microparticles were readily flocculated under small amount of SDS used;their shell thickness was enhanced as the amount of the monomer and crosslinker used was increased, but the excessive amount of the monomer and crosslinker used was helpful to the formation of pure poly(tert-butylmethacrylate) colloid particles and the flocculation of the formed core/shell composite microparticles. The morphological structure of the core/shell composite microparticles was confirmed by TEM. The fact that the silica cores of the composite microparticles were enwrapped by polymer was confirmed by contact angle measurements, and the microparticles were identified to be composed of silica and poly(tert-butylmethacrylate) by NMR and FTIR.