Synthesis of super-fine particles of poly (styrene-co-methyl methacrylate) by SPG emulsion polymerization

Abstract

Relatively uniform microspheres of poly (styrene-co-methyl methacrylate) were prepared employing a microporous glass membrane (Shirasu porous glass; SPG). The uniform monomer droplets were produced when monomer was allowed to permeate through the membrane pores under a controlled nitrogen pressure. The monomer droplets composed mainly of monomers, hydrophobic additives, and oil-soluble initiator, were suspended in the aqueous phase containing stabilizer and inhibitor, then transferred to a reactor, and subsequent suspension polymerization followed. The droplets obtained were polymerized at 75 ํC under a nitrogen atmosphere for 24 h. The uniform poly (styrene-co-methyl methacrylate) microspheres with diameters ranging from 7-14 microm, and a narrow particle size distribution with a coefficient of variation close to 10% were prepared using membranes pore size 1.42 microm. The effects of crosslinking agent, hydrophobic additives, oil-soluble initiator, the composition of the copolymer, and the addition of alkyl methacrylate monomers on the particle size, particle size distribution, morphologies were investigated. It was found that the particles size decreased with a narrow size distribution when the additives were changed from long-chain alkane to long-chain alcohols and long-chain esters, respectively. Various microspheres with different morphologies were obtained, depending on the composition of the oil phase. The spherical poly (styrene-co-methyl methacrylate) particle without phase separation was obtained when using an adequate amount of crosslinking agent and methyl palmitate as additive. Furthermore, the glass transition temperature (Tg) of copolymer can be controlled by the various fractions of lower Tg monomer of alkyl methacrylate monomers.