On the Curie temperature of poly(vinylidene fluoride).

In a previous study of copolymers of vinylidene fluoride (VF (2) and trifluoroethylene (F(3)E), we presented evidence suggesting that the Curie transition of PVF(2) homopolymer (in its piezoelectric Beta-phase) is centered above the melting point. However, other authors have proposed lower Curie temperatures (i.e., between 172C and 140C) that lie in fact below the melting point (175-185C for Beta-PVF(2). To help resolve this controversy, we have investigated the structure and transitions of VF(2) copolymers with tetrafluoroethylene (F(4)E) over a wide range of composition. We report here Curie temperatures for such copolymers in the range 64-81 mol% VF(2) that increase linearly with VF(2) content, leading to an extrapolated Curie transition for PVF(2) homopolymer at 195-197C. This provides strong support to our earlier proposal for the Curie transition in PVF(2), particularly because the F(4)(E) comonomer does not introduce new chemical species and stereoirregularity (as did F(3)E) but simply increases the number of head-head linkages that are already present in PVF(2).