Nonequilibrium Particle Morphology Development in Seeded Emulsion Polymerization. II. Influence of Seed Polymer Tg.

Most structured latex particles are formed in the nonequilibrium state as a result of the reaction kinetics proceeding faster than the phase separation kinetics. Of the many factors controlling such morphologies, the polarity and glass transition temperature (Tg) of the seed polymer are important. In order to study the direct effect of the seed polymer Tg on morphology, we produced a series of poly(methyl methacrylate)/poly(methyl acrylate) seed copolymers having glass points between 52 and 98°C, and particle sizes between 320 and 390 nm. We then used styrene as a second-stage monomer reacting in both the batch and semibatch process modes, and utilized reaction temperatures (Tr) between 50 and 70°C. Monomer feed rates were varied between flooded and starve-fed conditions. The equilibrium morphology for these composite particles is an inverted core-shell structure, but all morphologies obtained in our experiments were nonequilibrium. Under monomer starved conditions only core-shell structures were formed when (Tr-Tg) < 0, but significant penetration of the polystyrene into the acrylic core occurs when (Tr-Tg) > 15°C. These results are reasonably well predicted using the fractional penetration model developed earlier. © 2003 Wiley Periodicals, Inc.