The miscibility of poly(isobutyl methacrylate) with poly(styrene-co-acrylic acid) and of poly(isobutyl methacrylate-co-acrylic acid) with poly(styrene-co-N,N-dimethyl aminoethyl methacrylate) was studied by differential scanning calorimetry and inverse gas chromatography. Poly(styrene-co-acrylic acid), containing 20 or 32 mol% acrylic acid, and poly(isobutyl methacrylate) were immiscible, as were blends of poly(isobutyl methacrylate-co-acrylic acid) containing 10.5 mol% acrylic acid with poly(styrene-co-N,N-dimethyl aminoethyl methacrylate) containing 6 mol% of the basic comonomer. However, as a result of a higher level of favorable specific interactions between moieties in the two copolymers, the same isobutyl methacrylate copolymer or copolymers with a greater content of acrylic acid are miscible with the styrene copolymer containing 12 mol% N,N-dimethyl aminoethyl methacrylate, as suggested by the negative values of the apparent polymer-polymer interaction parameters.