Ferroelectric fluorinated copolymers with improved adhesion properties

Modified fluorinated electroactive poly(VDF-co-TrFE) copolymers with improved adhesion properties, on glass or metal substrates, are presented. Vinylidene fluoride (VDF) and trifluoroethylene (TrFE) were terpolymerized with 1 to 8 mol% of 2-(trifluoromethyl)acrylic acid (MAF) as an adhesion-promoting monomer. Monitoring the evolution of the reactor pressure and of the 19F NMR spectra of the terpolymer over the course of solution polymerization revealed the very pronounced compositional heterogeneity of the resulting terpolymer. The terpolymerization was scaled-up and implemented under aqueous suspension conditions in a 3 L-autoclave. This aqueous process, more industrially viable, was successful in spite of the undesirable addition reaction of water onto MAF producing 3-hydroxy-2-(trifluoromethyl)propanoic acid. The structure of the resulting polymers was characterized in detail by 1H, 19F NMR and FTIR spectroscopies, and their physical properties (thermal, adhesion and electroactive) were examined. The decarboxylation of MAF, observed by TGA to occur at ca. 250 °C, is not a limitation for the targeted applications. A MAF content of 1 mol% was shown to be sufficient to provide very good adhesion onto glass and metal substrates, and also to decrease the water contact angle from 104° (reference poly(VDF-co-TrFE) copolymer) to 86° (terpolymer containing 1 mol% of MAF). Polarization studies revealed that the terpolymers exhibited identical ferroelectric behavior as unmodified poly(VDF-co-TrFE) copolymers, characterized by a wide hysteresis (Ec = 60 MV m−1) and a high saturation polarization (Psat = 77 mC m−2). This study reports the first electroactive fluorocopolymers with improved adhesion, and paves the way for better incorporation of fluorinated electroactive thin films in multilayer films for flexible electronic devices.