Adhesive properties of high molecular weight acid copolymers used as hardeners for a commercial epoxy resin are investigated. For comparative purposes, physical blends of poly(acrylic acid)-polystyrene are used as hardeners. Joints prepared from physical blends exhibit lower lap shear strength than do those prepared from synthesis products. The use of copolymers is more adequate. Thermodynamic work of adhesion using wettability criteria is explored to explain the differences. The apparent energies of rupture determined by lap shear tests are 10(3) higher than those of the thermodynamic work of adhesion.