DISPERSION COPOLYMERIZATION OF STYRENE AND DIVINYLBENZENE .2. EFFECT OF CROSS-LINKER ON PARTICLE MORPHOLOGY

The amount of divinylbenzene (DVB) that can be incorporated in a one-s hot dispersion copolymerization with styrene to form a coagulum-free l atex is low (<0.5%), a consequence of steric stabilizer immobilization and the inability of the system to provide sufficient quantities of n ew stabilization materials. Inclusion of a polystyrene solvent in the charge and/or addition of excess stabilizer shortly after the nucleati on period enables 0.7% to be inserted, and up to 1% DVB can be copolym erized successfully by linear addition over the major particle growth period. Immobilization of some adsorbed stabilizer chains results in d eviations from sphericity. Microparticles ranging from classic smooth- surfaced spheres at low DVB concentrations to node covered cups and he avily dented spheres at higher levels, can be synthesized. Furthermore , batch addition of 1-6% DVB at least 7 h after nucleation produces mo nodisperse, stable latexes comprising particles bearing deformities du e, not to graft immobilization, but to phase separation within the cro sslinked 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. (C) 1996 Jo hn Wiley & Sons, Inc.