Crystalline forms in a copolymer of vinylidene fluoride and trifluoroethylene (52/48 mol %)

The structure of 52/48 mol % copolymer of vinylidene fluoride and trifluoroethylene has been investigated at various temperatures by X-ray diffraction. Melt-solidified samples consist of a mixture of two disordered crystalline phases, one trans-planar, the other 3/1-helical. Samples may be transformed to either phase by appropriate means to reveal a hexagonal (or pseudo-hexagonal) molecular packing. The all-trans phase may be obtained by drawing or poling at low temperatures; both treatments cause a transformation of the disordered mixture of phases into a well-ordered planar zig-zag phase. Isolation of the disordered 3/1-helical phase is achieved by heating to high temperatures, where-upon all samples, irrespective of orientation or polarization, undergo transformation to a poorly ordered helical structure analogous to that of trifluoroethylene homopolymer; upon cooling, the original, disordered mixture of phases is recovered. (Author)