Application of a series of novel chain-extended ureas as latent-curing agents and toughening modifiers for epoxy resin

A series of novel chain-extended ureas (Ui) containing poly(ethylene glycol) (PEG) spacers with different molecular weights were synthesized and the reactive mechanism, reactive activity, impact strength, dynamic mechanical behavior, morphology, and storage properties of the epoxy resin/chain-extended urea system were studied. Experimental results revealed that the impact strength of the epoxy resin modified with chain-extended urea containing a PEG flexible spacer with molecular weight of 1000 is 9.5 times higher than that of the epoxy resin/dicyandiamide system. Results also show that the molecular weight of PEG in chain-extended ureas hardly has any influence on the reactive activity of the chain-extended ureas. The storage life of the epoxy resin/Ui system can be delayed to 38 h at 50°C. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 339–347, 1998