Abstract
A series of urea derivatives were synthesized by reactions of amines and isocyanates and their acceleration effects on epoxy-dicyandiamide (DICY) curing system were studied. The focus of this study was the influence of substituents of the ureas on their acceleration effects, which clarified that the acceleration effects were almost independent on the isocyantederived part, but were strongly dependent on steric hinderance of the amine-derived part. The smaller steric hinderance of the amine-derived part was advantageous for the efficient acceleration of the curing system, implying that the ureas underwent thermal dissociation to give the corresponding amines, of which reactions with epoxide triggered the accelerated curing reactions. The noteworthy finding was the efficient acceleration by the ureas derived from cyclic amines, of which steric hinderance was smaller than the linear counterparts.
