Vinylidene fluoride structure

In 1991 MMM announced Fluorel II, a terpolymer of tetrafluoroethylene, vinylidene fluoride and propylene. As might be expected from the structure, this is intermediate between FKM and Aflas, having better resistance to many newer automotive oils, lubricants and transmission fluids than the former but better heat resistance than the latter. 

Likewise, poly (methyl methacrylate) and polyfvinylidene fluoride), the chemical structures of which are shown in Fig. 10.2, make a miscible blend because of the strong specific interactions between the oxygen atoms on the methacrylate and the fluoride group in the vinylidene fluoride group. 

Baltd-Calleja, F. J., Gonzalez Arche, A., Ezquerra, T. A., Santa Cruz, C., Batallon, F., Frick, B. and Lopez Cabarcos, E. Structure and Properties of Ferroelectric Copolymers of Poly(vinylidene) Fluoride. Vol. 108, pp. 1-48. 

Y. Takahashi and H. Tadokoro. Short-range order in form II of poly(vinylidene fluoride) antiphase domain structures , Macromolecules 16, 1880 (1983). 

The processability of fluorine-containing polymers is improved by replacement of one or more of the fluorine atoms. Replacing one of the eight fluorine atoms with a trifluoromethyl group gives a product called FEP or Viton, actually a copolymer of tetrafluoroethylene and hexafluoropropylene (Equation 6.53). Polytrifluoromonochloroethylene (PCTFE, Kel F) (Equation 6.54), in which one fluorine atom has been replaced by a chlorine atom, has a less regular structure and is thus more easily processed. Poly(vinylidene fluoride) (PVDF, Kynar) (Equation 6.55) is also more easily processable but less resistant to solvents and corrosives. 

Polymers such as polystyrene, poly(vinyl chloride), and poly(methyl methacrylate) show very poor crystallization tendencies. Loss of structural simplicity (compared to polyethylene) results in a marked decrease in the tendency toward crystallization. Fluorocarbon polymers such as poly(vinyl fluoride), poly(vinylidene fluoride), and polytetrafluoroethylene are exceptions. These polymers show considerable crystallinity since the small size of fluorine does not preclude packing into a crystal lattice. Crystallization is also aided by the high secondary attractive forces. High secondary attractive forces coupled with symmetry account for the presence of significant crystallinity in poly(vinylidene chloride). Symmetry alone without significant polarity, as in polyisobutylene, is insufficient for the development of crystallinity. (The effect of stereoregularity of polymer structure on crystallinity is postponed to Sec. 8-2a.)... 

Barium titanate is one example of a ferroelectric material. Other oxides with the perovskite structure are also ferroelectric (e.g., lead titanate and lithium niobate). One important set of such compounds, used in many transducer applications, is the mixed oxides PZT (PbZri-Ji/Ds). These, like barium titanate, have small ions in Oe cages which are easily displaced. Other ferroelectric solids include hydrogen-bonded solids, such as KH2PO4 and Rochelle salt (NaKC4H406.4H20), salts with anions which possess dipole moments, such as NaNOz, and copolymers of poly vinylidene fluoride. It has even been proposed that ferroelectric mechanisms are involved in some biological processes such as brain memory and voltagedependent ion channels concerned with impulse conduction in nerve and muscle cells. 

The copolymer of vinyl ferrocene (VF) and butadiene has also been reported in the literature for use as a binder for composite propellants. It does not require any burn-rate (BR) accelerator because of the presence of iron (Fe) in vinyl ferrocene which is converted to finely divided Fe203 (a well-known BR accelerator) during combustion. A few groups of scientists have also studied fluorocarbon polymers as binders for composite propellants because of their excellent compatibility with oxidizers and fuels coupled with high density. Accordingly, Kel-F elastomer (a copolymer of vinylidene fluoride and chlorotrifluoroethylene, trade name of 3M, USA) and Viton-A (copolymer of hexafluoropropylene and vinylidene fluoride, trade name of Du Pont, USA) have also been reported for this purpose. The structures of Kel-F 800 [Structure (4.13)] and Viton-A [Structure (4.14)] are ... 

Poly(vinylidene fluoride) PVDF2, has been studied by absorbance subtraction in order to isolate the spectral features of the different phases in particular, the difference spectra were used to interpret the structure of phase III212). The spectrum of the unoriented phase-III sample before annealing is shown in Fig. 15. The spectrum after annealing at 160 °C for 20 hr is also shown with the difference... 

A close correlation between the polarities of piezoelectricity and pyroelectricity was found for PVC and poly (vinylidene fluoride) (PVDF) films (Nakamura and Wada, 1971). However, it must be emphasized that the polarity of piezoelectricity is determined not only by the polarity of the charge distribution but also by that of heterogeneous strain. The origin of heterogeneous strain in the elongation of film may derive from heterogeneity in the structure of the film. 

Fig. 23. Crystal structure of /Worm (modification-/) poly (vinylidene fluoride). Figures in broken lines represent chain rotation to avoid the steric hindrance between F atoms (Hasegawa and others, 1970)...

Other halogenated copolymers, in which an isomorphous replacement is observed, were studied by Leshchenko, Karpov, and Kargin (19, 20) and later by Natta, Allegra, and Bassi (21). The former authors show that copolymers obtained from vinylidene fluoride and tetrafluoro ethylene are crystalline and show a tendency to altemance between the two types of monomer units (19). The same authors studied the vinylidene fluoride/hexafluoro propylene and the vinylidene fluoride/ trifluorochloro ethylene copolymer systems. In the former case crystallinity is observed up to contents of about 10% of the second component, the crystal structure being that of polyvinylidene fluoride. In the latter case crystallinity disappears for vinylidene fluoride contents in the order of 16%, the observed structure being that of polytrifluorochloro ethylene (20). 

The vinyl fluoride/vinylidene fluoride and the vinyl fluoride/tetra-fluoro ethylene copolymer systems were also studied (21). In the first case isomorphism is observed in the whole range of compositions, while the distribution of the two types of units is random. The crystal structure is that of polyvinyl fluoride, which is virtually identical with one of the three known crystalline forms of polyvinylidene fluoride, and characterized by a planar zig-zag chain conformation. High degrees of crystallinities in the whole range of compositions are also observed in the second case. However, the crystal structure of the two pure homopolymers is not the same hence we are in the presence of isodimorphism. In any case, for vinyl fluoride contents ranging between 0 and 75 mole-% the structure observed is essentially that of polytetrafluoro ethylene in the crystalline... 

Structure and Properties of Ferroelectric Copolymers of Poly(Vinylidene Fluoride)... 

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