Vinylidene fluoride- and trifluoroethylene-containing fluorinated electroactive copolymers. How does chemistry impact properties?

Fluoropolymers are attractive niche polymers used in high added value materials for high-tech applications in aerospace, electronics, coatings, membranes, cables, and the automotive industries. Among them, VDF- and TrFE-based copolymers exhibit remarkable electroactive properties allowing their incorporation 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 supplied. In addition to the polymer microstructure that may sometimes be controlled or influenced by the synthesis strategies, physical properties such as the phase transitions, and electroactivity are also affected by processing, such as annealing for example, and film thickness for example. Building on the conclusions and understanding obtained from the first section, the effect of the introduction of a termonomer (leading to poly(VDF-ter-TrFE-ter-M) terpolymers) is detailed in a second section of this review. Modifying the terpolymer chain microstructure has a major impact on the crystalline phase of the terpolymers that may result in a relaxor-ferroelectric behavior (RFE). The distribution of the termonomer along the polymer chain, the capacity of the termonomer units to enter the crystal lattice, as well as its dipole moment govern 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 the most studied. In two following sections, the block or graft architectures of VDF- and TrFE- based copolymers, and the various crosslinking strategies used so far for such copolymers are described. Chemical modification is indeed a very powerful tool to tune electroactive properties of copolymers or to impart additional properties. Finally, in the last section, a few examples of emerging applications for these fluorinated electroactive polymers (EAPs) are briefly discussed. This review aims to provide a comprehensive report on the use of polymer chemistry as a tool to produce better electroactive fluorinated polymers, and highlights possible opportunities and perspectives for future progress in this field. Research in this interdisciplinary 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 and fabrication of electronic devices. (C) 2017 Elsevier B.V. All rights reserved.