Super-fine particles of poly( styrene-co-methyl methacrylate) by dispersion copolymerization

Super-fine particles of sub-micron sizes of poly(styrene-co-methyl methacrylate) were synthesized by dispersion copolymerization in an ethanol-hexane mixture in the presence of a matrix polymer of poly(methyl vinyl ether). The effects of the matrix polymer, monomer feed ratio, ethanol-to-hexane ratio, and polymerization temperature were investigated for particle size and size distribution by SEM, molecular weights, and polydispersity index by GPC. Solubility of the matrix polymer in the medium to provide excluded free volumes in the polymer solution is plausibly the main attribute of controlling the morphology of the matrix polymer that directly affects the particle size and distribution in addition to its steric barrier effect. Particles with a spherical shape of 1-5 mu m were formed. The average molecular weights became larger in smaller particles. The copolymers in bulk and solution (without PMVE) were aggregated into a big lump. Increasing the styrene feed decreased the particle sizes with a narrow size distribution. Increasing the ethanol-to-hexane ratio decreased the copolymer particle sizes. The polymerization temperature range for the copolymerization was 50-64 degrees C. The reaction did not occur when polymerizing at 40 degrees C and the agglomerated particles were produced at a 73 degrees C reaction temperature. This article describes the effects of each parameter on the particle size and distribution. Solution and bulk copolymerizations were also carried out to compare the particle size and composition of the copolymer. (C) 1999 Elsevier Science B.V. All rights reserved.