Control of monodisperse particle size of styrenic-acrylate copolymers in dispersion copolymerization

Syntheses of monodisperse poly[(styrene)-co-(n-butyl acrylate)] and poly[(s tyrene)-co-(2-ethylhexyl acrylate)] were carried out by dispersion polymeri zation. The reactions were performed in the mixed solvent of ethanol-water in the presence of azo-bisisobutyronitrile and poly(N-vinylpyrrolidone) as the initiator and dispersant, respectively. The effects of reaction paramet ers, that is the type and concentration of dispersant, ratio of the mixed s olvent, reaction temperature, agitation rate, monomer composition between s tyrene and n-butyl acrylate or 2-ethylhexyl acrylate, crosslinking agent an d reaction time on the particle size, size distribution and average molecul ar weights of the resulting copolymer were thoroughly investigated. The res ulting copolymer particles were smooth on their spherical surface and the s izes were in the range 0.6-1.8 mum with a narrow size distribution. In most cases, a correlation between small particle sizes with high average molecu lar weights was observed. The average particle size generally increased wit h increasing reaction temperature, time and acrylate monomer content. In co ntrast, the particle size decreased as the molecular weight, concentration of dispersant, polarity of the medium or agitation rate was increased. The glass transition temperature (T-g) of the copolymers can be controlled by t he mole ratio of the comonomer. The T-g values decreased when the content o f acrylate monomers in the copolymer increased, and T-g values of the synth esized copolymer were in the range 66-102 degreesC. Instead of using n-buty l acrylate monomer in the copolymerization, 2-ethylhexyl acrylate copolymer ization with styrene resulted in insignificant changes in the particle size s but there were significant decreases in T-g values. In this study, the mo nodisperse particles can be obtained by monitoring the appropriate conditio ns regarding PVP K-30 (2-8 wt%), ethanol/water (90/10 wt%), the reaction te mperature (70 degreesC) and the agitation rate (100 rpm). (C) 2000 Society of Chemical Industry.