Summary: This contribution reports on a FT-IR study of the hydrogen bonding interactions within blends of different ratios of poly(styrene-co-methacrylic acid) containing 15 mol% of methacrylic acid PSMA-15 and poly(styrene-co-4-vinylpyridine) containing 15 mol% of 4-vinylpyridine PS4VP-15. Equilibrium constants describing both the self-association K 2 and inter-association K A in the (75:25) blend of poly-(styrene-co-methacrylic acid) containing 12 mol% of methacrylic acid PSMA-12 with poly(styrene-co-4-vinylpyridine) containing 22 mol% of 4-vinylpyridine PS4VP-22 were experimentally determined using a curve fitting analysis of the infra-red spectra. The FT-IR study at various temperatures confirms the miscibility of this blend up to 175 8C.