A novel method of nanoclay exfoliation in the synthesis of nanocomposites of PMR type thermoset resins was investigated. The method involves nanoclay intercalation by lower molecular weight PMR monomer prior to dispersion in primary, higher molecular weight PMR resin and resin curing to obtain the final composites. The resultant mechanical and thermal properties were evaluated as functions of clay type, degree of clay exfoliation, and clay intercalation strategies. It was found that sonication of clay at the time of intercalation by lower molecular weight PMR resin helps to achieve higher degree of exfoliation. In addition, clays obtained from ion exchange with a 50:50 mixture of N-[4(4-amino-benzyl)phenyl]-5-norborene-2,3-dicarboximide (APND), and dodecylamine (C12) showed better exfoliation than Cloisite (R) 30B clay. The resultant nanocomposites show higher thermal stability and higher tensile modulus. (c) 2007 Elsevier Ltd. All rights reserved.