AbstractThe miscibility and interactions of poly(vinyl nitrate) (PVN) / poly(vinyl methyl ketone) (PVMK) and poly(ethylene-co-vinyl nitrate) (EVN) / PVMK blends were investigated by differential scanning calorimetry and Fourier transform infrared spectroscopy (FTIR). PVN/PVMK blends were found to be miscible in the entire composition and temperature range. In addition, the compositional dependence of the glass transition temperature showed a positive deviation from the linear additivity rule, a phenomenon normally associated with compounds having attractive interactions. However, in this case, no attractive interactions between PVN and PVMK were identified by FTIR analyses. On the other hand, EVN/PVMK blends were found to be immiscible for most copolymer compositions, blend compositions and temperature ranges. Furthermore, intramolecular repulsive interactions of EVN were not apparent despite strong contrary expectations. Therefore, the phase behaviour in these blends was explained by a miscibility mechanism different from that of conventional polymer blends containing random copolymers.