STRUCTURE AND PROPERTIES OF FERROELECTRIC POLYMERS

Ferroelectric polymers can be divided into two classes. Class 1 consists of polar polymers having permanent dipoles in the direction perpendicular to the chain axis. The all-trans conformation and parallel packing produce the spontaneous polarization. Eventual 180 degrees rotations of individual molecules around their chain axes are responsible for polarization reversal. Conformational disorder causes the Curie transition. Vinylidene fluoride copolymers represent this class by exhibiting the fast switching phenomenon and the Curie point. Odd nylons and vinylidene cyanide copolymers show full or partial polarization reversal. Class 2 consists of liquid crystalline polymers adopting a chiral smectic C phase. Tilting of chiral molecules in the smectic layer induces the spontaneous polarization which is reversed by inversion of tilt direction. The Curie transition occurs as a result of loss of tilting. Fundamental properties characterizing the ferroelectric nature of these polymers are reviewed and discussed in relation to their structures.