Morphology development of 10-mu m scale polymer particles prepared by SPG emulsification and suspension polymerization

Classical particle morphologies, core-shell, hemisphere, sandwich, and so o n, were all reproducible by starting from ca. 10-mum uniform droplets compo sed of monomers, initiator, solvents, and polymer, and polymerizing them by subsequent suspension polymerization. SPG (Shirasu porous glass) membrane was employed to form uniform size droplets having the coefficient of variat ion (CV) around 10%. Styrene (ST) and acrylic monomers were used as monomer s, and their polymers were dissolved in the droplets to investigate the dev elopment of phase separation. When hydrophilic methyl methacrylate (MMA) wa s polymerized in the droplets with a mixed solvent consisting of hydrophili c hexanol (HA) and hydrophobic benzene and hexadecane (HD), the resulting m orphology shifted from hemisphere to sandwich and eventually to PMMA/solven t core-shell with increasing hydrophilicity of the mixed solvent. The sandw ich was converted to the core-shell after several weeks elapsed. As styrene was added to MMA, the morphology shifted from hemisphere core/solvent shel l to raspberry core/solvent shell as the fraction of ST increased. The doma in of the mixed solvent in the raspberry core was reduced with increasing t he hydrophilicity of the mixed solvent. All these morphologies were eventua lly converted to the copolymer core/solvent shell. When a mixed monomer of styrene and MMA dissolving polystyrene (PS) was polymerized, the resulting morphology shifted from salami to core-shell with increasing the MMA fracti on in the comonomer. The salami particles were then swollen with toluene, a nd after the swelling, toluene was removed under the different temperature and pressure. The final particle morphology converted to the core-shell wit h a milder rate of toluene removal which was predicted from the thermodynam ic model. When styrene and cyclohexyl acrylate (CHA), a pair with widely di fferent reactivity ratios, were copolymerized, salami morphologies, with ti ny CHA-rich domains dispersed in the matrix, were obtained even at a higher fraction of CHA in comonomer. Effects of glass transition temperature of t he polymers, molecular weight, and the composition of copolymers were taken in consideration whenever the final morphologies were discussed. By these experiments, the authors tried to demonstrate an advantage of using large u niform spheres for the particle morphology studies. SPG emulsification tech nique was a potential tool because of its free formulation of the droplets, and the subsequent polymerization could undergo without the breakup or coa lescence of the droplets. (C) 2001 John Wiley & Sons. Inc.