The inimitable geometry of novolac type phenolic resin (phenolic) and the strong inter-association cause the special microstructure in which the poly(hydroxyl ether of bisphenol A) (phenoxy) is sporadic in phenolic-rich region. Thermodynamic properties of the anomaly blend of phenolic and phenoxy were predicted by the Painter-Coleman Association Model. A modified method was used to obtain the equilibrium constant parameters that both polymers including self-association species, were utilised to describe the self-association and inter-association between the functional groups in the blend. The interaction of hydroxyl between phenolic and phenoxy is more competent than that of self-association of phenolic and phenoxy. The specific heat capacity (Cp) of the blend decreases with temperature, and the excess heat capacities (Delta Cp) of the blend are positive and approach zero while the temperature is high enough. Enthalpy is outstripped by entropy which causes the phase separation at. higher temperature. The LCST phase diagram was illustrated from the experimental results and theoretical prediction. The blend system exhibits complete miscibility within moderate temperature range from the results of thermodynamic property. (C) 1997 Elsevier Science Ltd.