Curing behaviour of IPNs formed from model VERs and epoxy systems Part II.Imidazole-cured epoxy

The polymerisation kinetics for IPNs formed from a model vinyl ester resin (VER) and an imidazole-cured epoxy resin (DGEBA) has been studied by scanni ng DSC and isothermal FTIR. The chemical interactions between the VER initi ating system (either cumene hydroperoxide, CHP; methyl ethyl ketone peroxid e, MEKP; benzoyl peroxide, BPO; or azobisisobutyronitrile, AIBN) and the ep oxy curative (l-methyl imidazole, 1-Mel) have been examined. IPNs containin g AIBN showed minimal initiator interactions but a strong accelerating effe ct was observed by the imidazole curing agent on the peroxide initiator sys tems (at least in the early stages) due to enhanced radical production appa rently via a redox reaction. For IPNs containing MEKP and BPO, the imidazol e also appeared to cause a significant loss of initiator activity, perhaps by non-radical redox side reactions. During the isothermal cure of the IPN, the DGEBA monomer acted as a diluent on the polymerisation of the ate-init iated Vinyl ester, resulting in a slower initial cure rate than in the neat VER. Due to the slower cure of the 1-Mel/DGEBA component, the DGEBA monome r acted as a plasticiser in the later stages of the isothermal VER cure, th us enabling higher final levels of vinyl cure prior to vitrification. As a consequence, the higher level of crosslinking of the VER component in the I PN reduced the maximum isothermal conversion of the epoxy component during its isothermal cure. (C) 2001 Elsevier Science Ltd. All rights reserved.