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Phase diagrams of poly(ethylene-co-vinyl alcohol) and dimethylformamide solutions exhibiting both liquid–liquid and solid–liquid phase separation



The binary solutions of poly(ethylene-co-vinyl alcohol) (EVOH), with 38 and 32 wt % ethylene content, and N,N-dimethylformamide were submitted to experiments to determine the cloud temperature by optical microscopy and the dynamic crystallization temperature by differential scanning calorimetry (DSC). The thermally induced phase separation (TIPS) process was used with the EVOH/DMF solutions that showed liquid–liquid phase separation at temperatures higher than EVOH crystallization and with a decrease of the temperature-UCST behavior. The binary interaction model was applied to estimate the interaction energy densities (B) considering both intermolecular (ethylene-Et/DMF and vinyl alcohol-VA/DMF) and intramolecular (Et/VA) interactions. According to this model the liquid–liquid line for the EVOH-38/DMF solutions should be situated at higher temperatures in comparison with EVOH-32/DMF solutions. Moreover, the phase separation results from low affinity between the hydrophobic segments of EVOH and the segments of the copolymer containing hydroxyl or the solvent. The equilibrium melting temperature of EVOH increases with the increase of EVOH volume fraction in the solution. This effect is more pronounced for EVOH-32/DMF solutions, which means that there is an influence of the VA content in EVOH during the melting. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010