The interfacial structure and properties of immiscible deuterated polystyrene (dPS)/epoxy bilayer films were investigated with neutron reflectivity as functions of the composition of the epoxy layer, the thickness of the dPS layer, and the annealing time. We have found that the interfacial width and its growth rate depend strongly on the compositions of the epoxy layer but only weakly on the thickness of the dPS layer. The effect of the resin/crosslinker composition on the interfacial width and its growth rate is likely due to the different near-surface structures that result for different epoxy stoichiometries. For an ultra-thin dPS film (thickness = 2R(g)), the data suggest a slight suppression of the growth of the interfacial width that could be due to confinement effects for the long-chain molecules such as have been previously reported for a thickness of less than approximately 4R(g), where R-g is the radius of gyration of polymer molecules.