Poly(vinylidene fluoride) (PVDF) and copolymers possess excellent ferro‐ and piezoelectric properties, and highly expected to be utilized as sensors in the areas covering the smart wearer, hydrophone, speaker, and medical ultrasonic devices. Besides PVDF in β crystalline phase, the copolymers with trifluoroethylene (TrFE) and tetrafluoroethylene (TFE) are widely investigated both in academia and industry. To illustrate how the steric hindrance between VDF and TrFE/TFE affects the condensed‐state structure and electric properties of the polymers, the electric properties and their dependences on molecular configuration and crystal structures of PVDF, P(VDF‐TrFE), and P(VDF‐TFE) are comparatively investigated. The introduction of same molar contents (20 mol%) of TrFE and TFE monomers into PVDF chain leads to the similar conformation transformation from α (γ ) phase to β phase and similar crystallinity in resultant P(VDF‐TFE) and P(VDF‐TrFE) thanks to the depressed energy of trans conformation and the increased energy barrier between anti‐gauche and trans conformation. That leads to the more preferred β‐phase and ferroelectric domains generated in P(VDF‐TrFE) and P(VDF‐TFE). Both the size of ferroelectric phase, the polarity of the polymer chain, the organization and orientation of the grains along the field are responsible for the excellent piezoelectric field resulted by the varied composition as well.
In the present work, poly(methyl methacrylate) (PMMA) is successfully grafted onto poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) side chains via directly activated CF bonds using Cu(0)/2,2′‐bipyridine as catalyst. The reaction mechanism and the initiating sites can be confirmed by the structure of the graft copolymer. The graft copolymerization exhibits first‐order kinetics, and reaction conditions can affect the chemical composition of the graft copolymer, including reaction time, reaction temperature, solvents, the amount of catalyst, and monomer. The introduction of rigid PMMA side chains onto P(VDF‐TrFE) can effectively tune the displacement–electric field hysteresis behaviors of P(VDF‐TrFE) from normal ferroelectric to anti‐ferroelectric, even linear‐like dielectric, under high electric field, resulting in dramatically reduced energy loss while maintaining the discharged energy density. This work may provide an effective strategy to introduce functional groups into P(VDF‐TrFE) copolymer via activation of CF bonds.
directly copolymerized VDF with vinyl acetate (VAc) monomer, and then hydrolyzed the VAc units to obtain P(VDF-VA) (VA, vinyl alcohol) copolymers exhibiting excellent electroactive properties. [14,15] As a controlled/living radical polymerization, atom transfer radical polymerization (ATRP) has been successfully used to synthesize well-defined homopolymers and copolymers of diverse architectures, [16,17] as well as graft copolymers from polymeric macro-initiators. Generally, the halogen atoms serve as initiation sites for the polymerization of side chains by ATRP. [18] In 2002, Mayes et al. reported the first graft copolymerization of methacrylates from PVDF via ATRP initiated by the secondary fluorines. [19] Subsequently, varied PVDF-based graft copolymers were obtained via direct activation of CF bonds using the same catalytic system. [20][21][22] However, the initiating efficiency was very low due to the low reactivity of secondary fluorine atoms, resulting in low grafting density in the graft copolymers. For instance, only about 0.1% of initiated fluorine atoms was observed in the resultant PVDFgraft-poly(tert-butyl methacrylate) (PVDF-g-PtBMA). To avoid the drawback of low initiating efficiency, Zhang et al. reported the graft copolymerization of styrene (St) and tert-butyl acrylate via ATRP from poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-CTFE)), [23] in which CCl bonds in CTFE were initiating sites. The obtained graft copolymers showed high grafting density and good distribution of grafts due to the relatively higher reactivity of the secondary chlorines. Furthermore, this strategy has been extensively employed for modification of commercial fluoropolymers to prepare various products with different performance and applications. [24][25][26][27] For instance, our group synthesized P(VDF-co-trifluoroethylene-co-CTFE)-graftpoly(ethyl methacrylate) (P(VDF-TrFE-CTFE)-g-PEMA) via ATRP route using CCl bonds in CTFE units, and the resultant copolymers exhibited adjustable dielectric and ferroelectric performances. [28][29][30] Meanwhile, TrFE bearing PVDF copolymers can be facilely obtained by atom transfer radical chain transfer (ATRCT) reaction from P(VDF-CTFE). [31] Besides, PVDF bearing inner CFCH bonds can be easily obtained by a controlled dehydrochlorination reaction of commercial P(VDF-CTFE) copolymer with organic base such as triethylamine. [32] The resultant copolymer could be crosslinked with radical initiators for rubber applications with high elongation. However, the strong electron withdrawing property of To endow new functions to poly(vinylidene fluoride) (PVDF) based fluoropolymers and expand their application fields, chemical modification is a useful tool to achieve this goal. In this work, the grafting of varied vinyl monomers onto PVDF backbone is achieved via the radical polymerization process using poly(vinylidene fluoride-co-trifluoroethylene) bearing CHCH double bonds (P(VDF-TrFE-DB)) as initiator, which is obtained by a controlled dehydrofluorination reaction of P(VDF-T...
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