Homopolymerization Effects in Polymer Layered Silicate Nanocomposites Based Upon Epoxy Resin: Implications for Exfoliation

Exfoliation of polymer layered silicate nanocomposites based upon epoxy resin has previously been reported to be enhanced by allowing some homopolymerization of the resin to occur, catalyzed by the onium ion of the organically modified clay, before the addition of the crosslinking agent and the curing of the nanocomposite. In this work we examine the effects of homopolymerization induced by pre-conditioning the resin/clay mixtures by storing them at various temperatures, from room temperature to 100 degrees C, prior to curing. It is found that pre-conditioning results in similar increases in both the epoxy equivalent (EE) and the glass transition temperature (T-g) of the resin as a consequence of homopolymerization, with a linear relationship between EE and T-g that depends on the pre-conditioning temperature. This is attributed to two different homopolymerization reaction mechanisms, activated monomer (AM) and activated chain end (ACE), the former dominating at high temperature and the latter at low temperature. The effects of these homopolymerization reactions on the network and nanostructure of the nanocomposite are discussed, the important aspect emerging being that the ACE mechanism is the one that most significantly enhances the exfoliation process. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 1040-1047, 2009