Dispersion copolymerization of styrene and divinylbenzene. II. Effect of crosslinker on particle morphology

Abstract

The amount of divinylbenzene (DVB) that can be incorporated in a one-shot dispersion copolymerization with styrene to form a coagulum-free latex is low (<0.5%), a consequence of steric stabilizer immobilization and the inability of the system to provide sufficient quantities of new stabilization materials. Inclusion of a polystyrene solvent in the charge and/or addition of excess stabilizer shortly after the nucleation period enables 0.7% to be inserted, and up to 1% DVB can be copolymerized successfully by linear addition over the major particle growth period. Immobilization of some adsorbed stabilizer chains results in deviations from sphericity. Microparticles ranging from classic smooth-surfaced spheres at low DVB concentrations to node covered cups and heavily dented spheres at higher levels, can be synthesized. Furthermore, batch addition of 1-6% DVB at least 7 h after nucleation produces monodisperse, stable latexes comprising particles bearing deformities due, not to graft immobilization, but to phase separation within the crosslinked particle skin that forms after DVB absorption. Lower amounts of divinyl monomer batch added before the 7-h mark permits synthesis of a variety of spheroidal and pod-shaped microparticles. © 1996 John Wiley & Sons, Inc.