Epoxy resin compositions comprising latent amine curing agents and novel accelerators

A thermally curable epoxy composition comprising

• A. an epoxy resin bearing a plurality of 1,2-epoxy groups;
• B. a latent amine curing agent for said epoxy resin;
• and
• C. a small but sufficient amount of at least one sterically hindered urea or thiourea accelerator to increase the rate of reaction between (A) and (B) at elevated temperatures;
• said accelerator corresponding to the formula ##SPC6##
• wherein:
• X is an atom of oxygen or sulfur;
• n is 1 or 2;
• R.sub.1 is lower alkyl, chloro or bromo;
• R.sub.2 is hydrogen, lower alkyl, chloro or bromo;
• R.sub.3 is hydrogen or an inert organic radical, or
• R.sub.1 and R.sub.2 or R.sub.1 and R.sub.3 can be joined to form a 5- or 6-membered carbocyclic ring;
• --NR.sub.4 R.sub.5 is the organic residue derived by the removal of the amino hydrogen atom from a secondary amine;
• with the proviso that R.sub.1 is located .alpha. on the benzene nucleus to at least one of the urea of thiourea substituents;
• and
• with the proviso that when n is 2, I is the position isomer having the urea or thiourea substituents located .alpha.,.alpha.' on the benzene nucleus with respect to R.sub.1, or, I is a mixture of position isomers consisting essentially of at least about 35 percent of the aforesaid .alpha.,.alpha.' position isomer and up to about 65 percent of the .alpha.,.gamma. isomer.