In-situ synthesis of PS/(−)silica composite particles in dispersion polymerization using an (±) amphoteric initiator

Abstract

Core/shell (±)PS/(−)silica nanocomposite particles were synthesized by dispersion polymerization using an amphoteric initiator, 2,2′-azobis [N-(2-carboxyethyl)-2,2-methylpropionamidine](HOOC(CH2)2HN(HN=) C(CH3)2CN=NC (CH3)2C(=NH)NH (CH2)2COOH), VA-057. Negatively charged (−6.9 mV) silica was used as the stabilizer. The effects of silica addition time and silica and initiator concentrations were investigated in terms of polymerization kinetics, ultimate particle morphology, and size/size distribution. Uniform hybrid microspheres with a well-defined, core-shell structure were obtained at the following conditions: silica content = 10−15 wt% to styrene, VA-057 content=above 2 wt% to styrene and silica addition time=0 min after initiation. The delay in silica addition time retarded the polymerization kinetics and broadened the particle size distribution. The rate of polymerization was strongly affected by the silica content: it increased up to 15 wt% silica but then decreased with further increase in silica content. However, the particle size was only marginally influenced by the silica content. The zeta potential of the composite particles slightly decreased with increasing silica content. With increasing VA-057 concentration, the PS microspheres were entirely coated with silica sol above 1.0 wt% initiator.