COOPERATIVE MOVEMENTS ASSOCIATED WITH THE CURIE TRANSITION IN P(VDF-TRFE) COPOLYMERS

The thermal and dielectric behavior of beta-PVDF and a series of rando m P(VDF-TrFE) copolymers with various chemical composition has been in vestigated in the temperature range of their Curie transition. Dielect ric relaxations and phase transitions were characterized by means of d ifferential scanning calorimetry and thermostimulated current spectros copy. The thermal hysteresis associated with the first order character of the Curie transition decreases as the TrFE content increases, and vanishes for P(VDF-TrFE) 50/50. For the latter, the distribution in la mellar thickness and the dependence of the conformational order in the ferroelectric phase upon thermal history yield an intricate thermal b ehavior. For the overall investigated polymers, the TSC mode associate d with the ferro/para-electric transition is described by a distributi on in relaxation times obeying a compensation law, This behavior has b een interpreted based on cooperative movements in the ferroelectric ph ase in the vicinity of the transition temperature. These molecular mov ements are precursors of the transition. It is valid for beta-PVDF, as well as for P(VDF-TrFE) copolymers which for the compensation tempera ture corresponds to the transition temperature. So, the Curie temperat ure of PVDF has been found at 170 degrees C, i.e. the melting point. ( C) 1995 John Wiley and Sons, Inc.