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 (U-i) containing poly(ethylene glycol) (PEG) spacers with different molecular weights were synthesize d and the reactive mechanism, reactive activity, impact strength, dyna mic mechanical behavior, morphology, and storage properties of the epo xy resin/chain-extended urea system were studied. Experimental results revealed that the impact strength of the epoxy resin modified with ch ain-extended urea containing a PEG flexible spacer with molecular weig ht of 1000 is 9.5 times higher than that of the epoxy resin/dicyandiam ide system. Results also show that the molecular weight of PEG in chai n-extended ureas hardly has any influence on the reactive activity of the chain-extended ureas. The storage life of the epoxy resin/U-i syst em can be delayed to 38 h at 50 degrees C. (C) 1998 John Wiley & Sons, Inc.