Miscibility, phase behavior, and Curie transition in blends of vinylidene fluoride/trifluoroethylene copolymer and Poly(1,4-butylene adipate)

Abstract

The phase diagram and Curie transition behavior in binary crystalline polymer blends of poly(vinylidene fluoride-trifluoethylene) P(VDF/TrFE) and poly(1,4-butylene adipate) (PBA) were investigated using differential scanning calorimetry, light scattering, and infrared spectroscopy. In order of descending temperature, the phase diagram exhibits a lower critical solution temperature (LCST), two crystal melting transitions, a paraelectric-ferroelectric phase transition, and a single glass transition. Liquid–liquid phase separation is observed at approximately 50°C higher than the melting points of P(VDF/TrFE) in the blends with PBA. The cloud point phase diagram is thermally reversible as typical for a true LCST. Increasing PBA concentration results in depression of the melting point of P(VDF/TrFE) in the blends. The analysis based on the melting point depression of P(VDF/TrFE) and PBA gives χ 12=−0.592 at 160°C and –0.071 at 61°C, respectively. Based on the shift of the CO absorption peak, the origin of miscibility in this blend was attributed to specific interactions between the CH 2 and/or CF 2 sites of P(VDF/TrFE) and the CO groups of PBA. The isothermal and non-isothermal crystallization behavior of P(VDF/TrFE) in the blends was analyzed in relation to the behavior of the ferroelectric-paraelectric phase transition, often known as the ‘Curie transition’. It was found that the addition of PBA (up to 70 wt%) increases the enthalpy of the Curie transition as well as the temperature of the Curie transition. Of particular interest is the possible formation of a ferroelectric phase directly from the melt without passing through the paraelectric phase in the high PBA compositions.