Blends composed of poly(vinylphenol) (PVPh) and bacterial (tactic) poly(hydroxybutyrate) (PHB) and synthetic (atactic) poly(hydroxybutyrate) (PHBa) have been investigated by FTIR. From quantitative analyses of hydrogen bonded PHB carbonyl groups as a function of temperature and composition, the interassociation constant, K-A, describing the formation of hydroxyl-carbonyl interaction as well as the related enthalpy of hydrogen bond formation have been determined. Using the association model of Painter and Coleman, phase diagrams have been predicted for blends of PVPh with the poly(hydroxyalkanoate) family.