CURING OF DICYANDIAMIDE EPOXY-RESINS ACCELERATED WITH SUBSTITUTED UREAS

An epoxy resin based on bisphenol-A-diglycidylether (DGEBA) was cured with dicyandiamide (DDA) and different substituted ureas (Urones) as a ccelerators. Differential scanning calorimetry, size exclusion chromat ography, and Fourier transform infrared (IR) analysis indicated comple x reaction mechanisms. The DDA granulometry seemed not to be a predomi nant parameter, but its content clearly influences T-g of the network. The maximum T-g value was found for an amine-to-epoxy molar ratio of 0.6. IR spectra revealed the appearance of oxazolidone rings, which ar e the first product of epoxy reactions. Urone accelerators also acted as homopolymerization initiators; they modified the epoxy conversion a t gelation and changed of the structure of the obtained network. Influ ence of uron nature and content on reaction rates were also studied. ( C) 1998 John Wiley & Sons, Inc.