Two PMMA-epoxy-clay ternary composites have been produced combining the polymerization induced phase separation phenomenon with two individual dispersion processing methods: a melt-blending and an ultrasonic-blending. Transmission electron microscopy (TEM) analysis shows that phase separation between PMMA and epoxy network was obtained in the form of spherical nodules in both processing methods. Organoclay particles were finely dispersed into thermosetting network and predominantly delaminated in ultrasonic-blending, whereas organoclays formed micrometer-sized aggregates in melt-blending. Wide-angle-X-ray (WAXS) studies reveal that exfoliation in the clay particles in three-phase composite was reached. Exfoliation state has been investigated using small angle X-ray scattering (SAXS) in cured systems and during curing reaction. For reacted systems, an exfoliation of platelets can occur through the de-aggregation of large agglomerates into smaller particles composed of a few platelets. For in situ SAXS studies, the distribution of the thicknesses of diffusing entities and the evolution of this distribution with reaction time were followed. This technique has shown also that movements at scale of nanometers of clay tactoids are possible even after the gel point. (c) 2007 Elsevier Ltd. All rights reserved.