Conformation of PVF2 and Its Copolymers in the Crystalline Phases

As pointed out above, the occurrence of a pronounced piezoelectric effect in synthetic polymers can be mainly attributed to the presence of a non-eentro-symmetric unit cell and a net polarization in the material. To achieve this in polymeric materials one requires [28] (a) a large dipole moment in the chemical repeat unit (b) feasibility of crystallizing in a non-centrosymmetric unit cell (c) alignment of molecular dipoles. A dipole moment arises from a 

Copolymers of VF2 with trifluoroethylene are randomly added copolymers. Those containing a mole fraction of VF2 of 50-80% have been widely studied. Since they contain a greater proportion of the comparatively bulky fluorine atoms than PVF2 their molecular chains cannot accommodate the tg+tg conformation and crystallize at room temperature in the ferroelectric phase with the extended all-trans planar conformation [37] with small statistical deviations away from that plane, i.e. copolymers of VF2 with F3E crystallize essentially with the same conformation as P-PVF2. 

Copolymers of VF2 and trifluoroethylene also exhibit a Curie temperature at which the ferroelectric crystals show reversibly a solid state transformation to 

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