Styrene copolymers containing about 4.3, 7.5 and 13.3 mol% of 4-vinylbenzenephosphonic acid (VBPA) as comonomer units were synthesized. The copolymers were insoluble in common organic solvents, possibly because side reactions involving the phosphonic acid-groups had occurred during the drying process. Upon adding a small amount of concentrated hydrochloric acid to tetrahydrofuran, the polymer became soluble. The miscibility of blends of styrene copolymers (PSVBPA) containing VBPA units with poly(n-butyl methacrylate) (PBMA) and with poly(vinyl methyl ether) (PVME) were studied using differential scanning calorimetry and Fourier transform infra-red spectroscopy. All three copolymers were immiscible with PBMA over the entire composition range. Infra-red spectra indicated no observable interactions between the phosphonic acid and -C=O groups in the blends. Blends of PSVBPA-13.3/PVME were also immiscible over the entire composition range. When PSVBPA-7.5 and PSVBPA-13.3 were mixed with styrene copolymers containing 7.5 and 13.3 mol% of 4-vinylbenzenephosphonic acid diethyl ester, the latter being a strong hydrogen-bond acceptor, the blends appeared to be miscible.