Provided is a curable composition containing a reactive mixture of components including an polyethersulfone having a chemical group reactive with an epoxide, a cycloaliphatic polyepoxide resin, a polyepoxide having a functionality greater than two, a liquid diepoxide resin, a first curative containing 9,9-bis(aminophenyl)fluorene or a derivative therefrom and having a curing onset temperature of from 150° C. to 200° C. The components can further comprise a second curative having a curing onset temperature of from 60° C. to 180° C. When thermally curing this composition, the second epoxy curative starts to cure before the first epoxy curative, thereby inhibiting vertical flow of the adhesive during the curing process.