IntroductionComposite polymers are an increasingly important class ofmaterials and they can be produced as simple blends of individualpolymers (as in melt blending and latex blends), by solvent evap-oration from solutions of polymers, or from reactive processing.In the latter case one polymer is usually created in the presence ofanother (first stage, or seed) polymer. In all cases there is the poten-tial for portions of the composite material to be mixed, whetherit be in natural interfaces between phase separated polymers orin zones of kinetically frozen (non-equilibrium) polymer mixtures.The former are inherent to the polymers involved while the latterare largely due to processing conditions and restraints on the phaseseparation process during and after reaction. The production ofcomposite latex particles via starve-fed seed latex polymerizationis particularly prone to producing significant amounts of kineticallyfrozen mixtures and has been the subject of much of our research.