Electron microscopic observation of uniform macroporous particles. I. Effect of seed latex type and diluent

Uniform and macroporous polymer particles in the size range of 5-21 mu m we re prepared by a multistep seeded polymerization method. The uniform polyst yrene particles in the size range of 1.9-7.5 mu m were used as the seed par ticles in the preparation of macroporous beads. The seed particles with dif ferent sizes and molecular weights were produced by dispersion polymerizati on, by changing the type of dispersion medium and the initiator concentrati on. In the synthesis of macroporous particles, a two-step swelling procedur e was employed. The seed latexes were first swollen by a low molecular-weig ht organic agent (i.e., dibutyl phthalate, DBP), then by a divinylbenzene-e thylvinylbenzene isomer mixture including an oil phase soluble initiator (i .e., benzoyl peroxide). The porous structure in the final beads was achieve d by the polymerization of the monomer phase within the swollen seed partic les including a mixture of linear polystyrene and DBP. The initiator concen tration in the repolymerization step, the seed latex type (i.e., the diamet er and the molecular weight of seed latex), DBP/seed latex, and the monomer /seed latex ratios were changed to achieve uniform polymer beads with diffe rent average sizes and pore structures. The average size, the size distribu tion, and the surface morphology of final beads were analyzed by Scanning E lectron Microscopy. The internal structure of the beads were analyzed by Tr ansmission Electron Microscopy. The results indicated that the average size of the final particles increased with increasing the seed latex diameter, DBP/seed latex, and monomer/seed latex ratios. The average pore size decrea sed with decreasing the molecular weight of the seed latex and increasing t he DBP/seed latex and monomer/seed latex ratios. These tendencies were expl ained by the viscosity change of the porogen solution used in the repolymer ization step. (C) 1999 John Wiley & Sons, Inc.