Curing behaviour of IPNs formed from model VERs and epoxy systems I amine cured epoxy

The curing behaviour for an Interpenetrating Polymer Network (IPN) formed f rom a model Vinyl ester resin (VER) and an amine cured epoxy resin has been studied by scanning DSC and isothermal mid-FTIR. The interactions between the VER initiating system (azobisiso-butyronitrile or cumene hydroperoxide, benzoyl peroxide or methyl ethyl ketone peroxide/cobalt octoate) and the e poxy curative (aniline, diaminodiphenyl methane, butylamine or diamino-octa ne) have been examined. For most of the IPNs, there was evidence for a redu ction in reaction rate due to the dilution of each reacting system by the o ther resin components. When cumene hydroperoxide, benzoyl peroxide or methy l ethyl ketone peroxide (with or without cobalt octoate) were used as the r adical initiating systems, there was strong redox interaction between the p eroxide and the amine, which caused acceleration of the peroxide decomposit ion in the early stages of reaction and also resulted in premature depletio n of the initiator system. Evidence for a grafting reaction between the ami nes and the methacrylate groups by Michael addition was also found. In some systems cured isothermally at 70 degreesC, the slow cure of the epoxy comp onent allowed the unreacted DGEBA to plasticise the system and enhance the extent of cure of the VER components prior to vitrification of the IPN. As a consequence of the additional crosslinks introduced by the VER component, premature vitrification occurred during the slower cure of the DGEBA compo nent, thus reducing the extent of cure of the epoxy groups in the IPN. Near full cure could be obtained for most of the IPN systems when post-cured at elevated temperature, indicating that the presence of each network imposed minimal topological restrictions on cure. (C) 2000 Elsevier Science Ltd. A ll rights reserved.