The technique of inverse gas chromatography (IGC) has been used to evaluate the acid-base interaction potential of two polybenzoxazines. One of these, prepared from bisphenol-h monomer, was shown to be a net base. Another based on dihydroxybenzophenone registered as a net acid. The bisphenol-A version was adsorbed at controlled thicknesses on ct-alumina, on fumed silica and on boron nitride, all three solids with acidic surfaces as shown by IGC data. Thin layers of the adsorbed polymer near monolayer coverage were strongly perturbed by the underlying substrate, the polymer surface now behaving as a net acid. Thicker layers of the adsorbed polymer revert to basicity, but fail to attain the acid-base interaction constants of the pure polymer. The presence of strongly interactive substrates leads to the creation of a substantial interphase, the interaction properties of the adsorbed polymer varying through the thickness of this layer.