Achieving a high degree of exfoliation in epoxy-based polymer layered silicate (PLS) nanocomposites is crucial to their successful industrial application, but has hitherto proved elusive. In this work, a system is presented which shows significant promise in this respect. The isothermal cure of PLS nanocomposites based upon a tri-functional epoxy resin (TGAP) has been studied by DSC, and displays two exothermic peaks. The first peak, very rapid, relates to a homopolymerization reaction within the intra-gallery regions, while the second peak reflects the bulk crosslinking reaction. The occurrence of the intra-gallery reaction before the bulk reaction enhances the degree of exfoliation in the cured nanocomposite. Furthermore, pre-conditioning the resin/clay mixture before adding the curing agent and effecting the isothermal cure also allows a greater extent of intra-gallery reaction to occur before the extra-gallery epoxy-amine reaction. Consequently, this system results in a high degree of exfoliation, as revealed by transmission electron microscopy. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013