In this work a Fourier transform infrared (FTIR) study of blends of styrene-vinyl phenol copolymers (containing different proportions of styrene) with atactic PHB is presented. The equilibrium constant describing phenolic OH/ester carbonyl hydrogen bonds (K-A) has been experimentally determined from the quantification of the hydrogen-bonded carbonyl group fraction as a function of temperature, and the effect of functional group accessibility on K-A values has been discussed. An average value of K-A = 41 has been employed to perform a prediction of miscibility maps employing the association model of Painter and Coleman. A fairly good agreement between theoretical predictions and experimental results has been obtained. (C) 2003 Elsevier Ltd. All rights reserved.