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 (T-g) of the seed polymer are important. In order to study the direct effect of the seed polymer T-g on morphology, we produced a series of poly(methyl methacrylate)/poly(methyl acrylate) seed copolymers having glass points between 52 and 98degreesC, and particle sizes between 320 and 390 nm. We then used styrene as a second-stage monomer reacting in both the batch and semi-batch process modes, and utilized reaction temperatures (T-g) between 50 and 70degreesC. 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 (T-r-T-g,) < 0, but significant penetration of the polystyrene into the acrylic core occurs when (T-r -T-g) > 15degreesC. These results are reasonably well predicted using the "fractional penetration" model developed earlier.