Dependence of morphological changes of polymer particles on hydrophobic/hydrophilic additives

Fairly uniform microspheres of poly(styrene-co-methyl methacrylate) were pr epared by employing a microporous glass membrane [Shirasu porous glass (SPG )]. The single-step SPG emulsification, the emulsion composed mainly of mon omers, hydrophobic additives, and an oil-soluble initiator, suspended in th e aqueous phase containing a stabilizer and inhibitor, was then transferred to a reactor, and subsequent suspension polymerization followed. The dropl ets obtained were polymerized at 75 degrees C under a nitrogen atmosphere f or 24 h. The uniform poly(styrene-co-methyl methacrylate) microspheres with diameters ranging from 7 to 14 mu m and a narrow particle-size distributio n with a coefficient of variation dose to 10% were prepared by using SPG me mbrane with a pore size of 1.42 mu m. The effects of the crosslinking agent and hydrophobic additives on the particle size, particle-size distribution , and morphologies were investigated. It was found that the particle size d ecreased with a narrower size distribution when the additives were changed from long-chain alkanes to long-chain alcohols and long-chain esters, respe ctively. Various microspheres with different morphologies were obtained, de pending on the composition of the oil phase. The spherical poly(styrene-co- methyl methacrylate) particles without phase separation were obtained when using an adequate amount of the crosslinking agent and methyl palmitate as an additive. (C) 2000 John Wiley & Sons, Inc.