ABSTRACT
Porous particles of micrometer size have been prepared using the concentrated emulsion polymerization method. The dispersed phase with a volume fraction greater than 0.74 contained a monomer, or a polymer, a crosslinking agent, and inert liquids as porogens. The continuous phase consisted of an aqueous solution of a surfactant when the monomer of the dispersed phase was hydrophobic, and a surfactant solution in a hydrocarbon liquid when the dispersed phase was hydrophilic. Four kinds of porous materials have been achieved: (1) hydrophobic crosslinked (with divinylbenzene (DVB) as the crosslinking agent) polystyrene particles; (2) hydrophilic crosslinked polyacrylamide (with methylenebisacrylamide (MBAA) as the crosslinking agent) particles; (3) hydrophobic porous nutshells of crosslinked polystyrene surrounding a void filled with sparse poly(vinylbenzyl chloride) (poly(VBC)); and (4) hydrophilic nutshells of crosslinked polyacrylamide encapsulating loosely entangled polyethylene oxide coils. The nutshell structure was obtained by using a two-step procedure: First, a concentrated emulsion of oil in water (o/w) with a dispersed phase consisting of monomers (VBC and DVB) dissolved in a porogen was polymerized, or a concentrated emulsion of water in oil (w/o) in which the dispersed phase contained a polymer 182polyethylene oxide dissolved in water was prepared. In the second step, styrene/DVB was introduced into the o/w emulsion and an aqueous solution of acrylamide/MBAA into the w/o emulsion. The resulted systems were allowed to polymerize, thus generating polymer shells encapsulating either sparse poly(VBC) matrixes or loosely entangled polyethylene oxide. The porous hydrophobic polymeric beads of the first kind have relatively small surface areas of 20–40 m2/g, while those of the third kind have surface areas of about 300 m2/g. The crosslinked particles of polyacrylamide of the second kind were prepared with water as the porogen adsorbs 68 mg of enzyme lipase per gram of polymer. The poly(VBC) encapsulated in the porous nutshell particles was functionalized with anchoring quaternary phosphonium cations. This functionalized substrate possesses a high adsorption capacity for cobalt carbonyl anions (2.78 mmol of Co/g of polymer) via ion pair formation as well as via physical adsorption.
