Abstract:
Syntheses of monodisperse poly(styrene-co-n-butyl acrylate) and poly(styrene-co-2-ethylhexyl acrylate) were carried out by dispersion polymerization. The reactions were performed in the mixed solvent of ethanol-water in the presence of poly(N-vinylpyrrolidone) and azo-bisisobutyronitrile as matrix polymer and initiator, respectively. The effects of reaction parameters, that is, type and concentration of matrix polymer, ratio of the mixed solvent, reaction temperature, agitation rate, monomer composition between styrene and n-butyl acrylate or 2-ethylhexyl acrylate, crosslinking agent, and reaction time on the particle size, size distribution, and average molecular weights of the resulting copolymer were thoroughly investigated. The particle size and size distribution were measured by SEM, the average molecular weights by GPC, the functional groups and the copolymer composition by FTIR and NMR, and the thermal property by DSC. The resulting copolymer particles were smooth on their spherical particle surface and the particle sizes were in the range of 0.6-1.8 mum with a narrow size distribution. In most cases, the correlation between small particle sizes with high average molecular weights was observed. The average particle size generally increased with increasing reaction temperature, time, and acrylate monomer content. In contrast, the particle size decreased as molecular weight, concentration of matrix polymer, polarity of the medium, and agitation rate were increased. The glass transition temperature (Tg) of the copolymers can be controlled by the mole ratio of the comonomer. Tg values decreased when the content of acrylate monomers in the copolymer increased, and Tg values of the synthesized copolymer were in the range of 66-102 ํC. Instead of using n-butyl acrylate monomer in the copolymerization, 2-ethylhexyl acrylate copolymerization with styrene resulted in insignificant change in the particle sizes but with the significant decrease in Tg values. In this study, the monodisperse particles can be obtained by monitoring the appropriate conditions with PVP K-30 (2-8 wt%), ethanol/water (90/10 wt%), reaction temperature (70 ํC), and agitation rate (100 rpm). This research work can explain the roles of solubility parameter of the system on particle size and size distribution of the copolymeric particles.
