Phase Behavior and Ferroelectric Transitions of Poly(Vinylidene Flouride) as Functions of Molecular Structure

Poly(vinylidene flouride) [PVF2] normally contains ca. 3.5 - 5.5 mol % head-head/tail-tail (HHTT) units (i.e., CF2-CF2-CH2-CH2). However, as a result of recent syntheses of PVF2 specimens having a HHTT content in the 0.2 - 23.5 mol % range, we have now been able t study the role of molecular defects on the structure, crystallization, and ferroelectric transitions of this polymer. The crystallization process favours the polar Beta-phase over the antipolar, as the HHTT content is increased beyond ca. 11.4 mol %. At higher HHTT contents, progressive intramolecular disorder is introduced. For samples containing 13.5 - 15.5 mol % HHTT units, we have obtained the first evidence for clear, reversible Curie transitions in PVF2, homopolymer. We have also studied such transitions in PVF2 copolymers with tetrafluoroethylene, in which the content of the latter (equivalent to head-head units without tail-tail counterparts) could be varied from 0 to 100 mol %.