Poly (methyl methacrylate) (PMMA) was known to be miscible with poly (vinyl phenol) (PVPh). According to literature, poly (vinyl cinnamate) (PVCN) was also miscible with PVPh. The miscibility between PMMA and PVCN was corroborated on the basis of preliminary experiments. Is a ternary blend consisting of PMMA, PVPh and PVCN miscible in all the blend compositions? To answer this question, the miscibility of this ternary was examined in different blend compositions mainly based on calorimetry data in this investigation. The results using two different molecular weights of PVPh demonstrated an interestingly closed-loop behavior of immiscibility. The reason is likely because of the "Delta chi effect". (c) 2006 Elsevier B.V. All rights reserved.