Heat-curable compositions exhibiting improved room temperature pot life and reduced viscosity are obtained from composition comprising a polyepoxide, an aromatic or aliphatic amine, a trihydrocarbyl sulphonium salt, a free radical curing agent and an unsaturated monomer selected from vinylaromatic monomers, alkylesters of unsaturated carboxylic acids, cyano-compounds, vinyl-ester, N-vinylames and allyl compounds.