The effect of montmorillonite clay (MMT) platelets on the morphol. of polystyrene¿/poly(Me methacrylate) (PMMA) composite latex particles prepd. via PMMA-¿seeded (semi-¿) batch emulsion polymn. of styrene was studied. The particle morphol. obtained greatly depended on the ability of the clay platelets to diffuse through the polymer particle. Indeed, when the reactions were strictly under kinetic control, i.e., where the clay platelets were unable to diffuse during polymn., anisotropic core-¿shell-¿like morphologies with split core were obsd. A better mobility of the clay platelets could more or less restrict the diffusion of the second-¿stage polymers within the host polymer, leading to original kinetically controlled morphologies. In the case of a full migration of the clay platelets to the particle surface, the penetration of the second-¿stage polymer species in the seed latex was more limited, enhancing the formation of secondary particles.