The miscibility and interactions in blends and complexes of poly(4-methyl-5-vinylthiazole) (PMVT) with poly(p-vinylphenol) (PVPh), poly(acrylic acid) (PAA) and poly(vinylphosphonic acid) (PVPA) were studied. PMVT formed complexes with PVPA but not with PVPh and PAA. Each of the blends of PMVT with PVPh and PAA showed a single glass transition temperature (T-g), indicating miscibility. Fourier-transform infrared spectroscopic and X-ray photoelectron spectroscopic studies provided the existence of interactions in the PMVT blends and complexes. The XPS studies indicated that the thiazole nitrogen atoms are involved in hydrogen-bonding interactions with PVPh and PAA, and ionic interactions with PVPA. The sulfur atoms of PMVT also interact with PVPh, PAA and PVPA. (C) 2003 Published by Elsevier Ltd.