The intermolecular hydrogen bonding interactions between poly(3-hydroxybutyrate) and poly(styrene-co-vinyl phenol) copolymers with mutual solvent epichlorohydrin were thoroughly investigated by steady-state fluorescence and viscosity techniques. Fluorescence spectroscopy along with viscosity technique was used to asses the intermolecular hydrogen bonding between poly-(3-hydroxybutyrate) and its blends with five copolymer samples of styrene-vinyl phenol, containing different proportions of vinyl phenol but similar average molecular weight and polydispersity index. In the case of very low OH contents (2-4 mol %), as expected, both components of poly(3-hydroxybutyrate) and poly(styrene-co-4-vinylphenol) chains are well separated and remain so independently of the mixed polymer ratio and overall polymer concentration as well. Conversely, when the OH content reaches 5.8 mol % or more, a significant decrease of the intrinsic fluorescence intensity emitted by the copolymer is detected upon addition of aliquots of poly(3-hydroxybutyrate). In these cases, an average value for the interassociation equilibrium constant, K-A = 8.7, was obtained using a binding model formalism. A good agreement of these results with those obtained from complementary viscosity measurements, through the interaction parameter, Delta b, was found. (c) 2006 Wiley Periodicals, Inc.