Vinylidene fluoride- and trifluoroethylene-containing fluorinated electroactive copolymers. How does chemistry impact properties?
Résumé
Fluoropolymers are attractive niche polymers used in high added value materials for high-tech appli-cations in aerospace, electronics, coatings, membranes, cables, and the automotive industries. Amongthem, VDF- and TrFE-based copolymers exhibit remarkable electroactive properties allowing their incor-poration into a wide range of devices such as printed memories, sensors, actuators, artificial muscles,and energy storage devices. In a first section, a detailed overview of semi-crystalline poly(VDF-co-TrFE)copolymers and of their ferroelectric (FE) properties from the point of view of polymer chemists is sup-plied. In addition to the polymer microstructure that may sometimes be controlled or influenced by thesynthesis strategies, physical properties such as the phase transitions, and electroactivity are also affectedby processing, such as annealing for example, and film thickness for example. Building on the conclusionsand understanding obtained from the first section, the effect of the introduction of a termonomer (leadingto poly(VDF-ter-TrFE-ter-M) terpolymers) is detailed in a second section of this review. Modifying theterpolymer chain microstructure has a major impact on the crystalline phase of the terpolymers that mayresult in a relaxor-ferroelectric behavior (RFE). The distribution of the termonomer along the polymerchain, the capacity of the termonomer units to enter the crystal lattice, as well as its dipole momentgovern in large part the terpolymer electroactive properties. Poly(VDF-ter-TrFE-ter-CFE) and poly(VDF-ter-TrFE-ter-CTFE) terpolymers appeared to be the best candidates for RFE properties and were thus themost studied. In two following sections, the block or graft architectures of VDF- and TrFE- based copoly-mers, and the various crosslinking strategies used so far for such copolymers are described. Chemicalmodification is indeed a very powerful tool to tune electroactive properties of copolymers or to impartadditional properties. Finally, in the last section, a few examples of emerging applications for these fluo-rinated electroactive polymers (EAPs) are briefly discussed. This review aims to provide a comprehensivereport on the use of polymer chemistry as a tool to produce better electroactive fluorinated polymers, andhighlights possible opportunities and perspectives for future progress in this field. Research in this inter-disciplinary field requires different kinds of expertise, ranging from organic and polymer chemistries,polymer films engineering, physics of semi-crystalline polymers and electroactivity, to the design andfabrication of electronic devices.