Differences in electroactive terpolymers based on VDF, TrFE and 2,3,3,3-tetrafluoropropene prepared by batch solution and semi-continuous aqueous suspension polymerizations

Abstract

In the search for new fluorinated electroactive copolymers, 0–8 mol% of 2,3,3,3-tetrafluoropropene (1234yf) was terpolymerized with vinylidene fluoride (VDF) and trifluoroethylene (TrFE). The reactivity in batch solution polymerization of 1234yf was evaluated. First, reactivity ratio measurements showed that homopropagation of 1234yf is favored compared to cross propagation with VDF or TrFE (r_VDF-1234yf = 0.079, r_1234yf-VDF = 2.6; and r_TrFE-1234yf = 0.089, r_1234yf-TrFE = 4.9, at 48 °C). Then, the study of a typical batch solution polymerization revealed that the polymerization time was not affected by the initial amount of 1234yf and that polymer chains with strong compositional heterogeneity were obtained. Based on these results, a semi-continuous aqueous suspension polymerization process was used for the synthesis of terpolymers with a more homogeneous composition. Calculation of addition probabilities exemplified the changes in the drift of composition. The monomer sequences in the poly(VDF-ter-TrFE-ter-1234yf) terpolymers, carefully studied by ¹⁹F NMR spectroscopy, were not affected by the polymerization process and were dominated by VDF-TrFE and VDF-1234yf dyads. Finally, the thermal and ferroelectric (FE) properties of the homogeneous and heterogeneous terpolymers were characterized and compared. In the case of heterogeneous terpolymers, increasing the 1234yf content from 0 to 6 mol% slightly decreased the crystal size and the overall crystallinity (T_m = 60 °C and ΔH_m = 144 J g⁻¹ for a poly(VDF₆₆-ter-TrFE₂₆-ter-1234yf₈) terpolymer). On the contrary, for homogeneous terpolymers, 5 mol% of 1234yf strongly affected both the Curie and melting transitions at T_Curie = 37 °C and T_m = 107 °C. The reduced coercive field (E_c = 40 MV m⁻¹) and remnant polarization (P_r = 22 mC m⁻²) for the homogeneous terpolymer compared to a reference poly(VDF₆₅-co-TrFE₃₅) (E_c = 62 MV m⁻¹ and P_r = 45 mC m⁻²) transcribed modifications of the FE domains.