Poly(vinylidene fluoride) (PVDF) based relaxor ferroelectric polymers show great potential for applications in transducers, sensors and artificial muscles for their excellent electrostrictive properties. The all-trans chain conformation of the current relaxor has to be stabilized by special monomers, such as trifluoroethylene or tetrafluoroethylene units, whose lower dipole moment than VDF leads to reduced dielectric and electrostrictive properties. Directly stretching the PVDF copolymers with bulky units, such as P(VDF-CTFE) and P(VDF-HFP) (CTFE and HFP refer to chlorotrifluoroethylene and hexafluoropropylene), has failed in fabricating PVDF relaxors for the too large steric hindrance of CTFE and HFP units. In the present work, we reported the special strategy of uniaxially stretching a family of PVDF polymers tailored by CFCH bonds with smaller steric bulk to realize tunable ferroelectric performances for piezoelectric and electrostrictive applications. The pinning effect of CFCH bonds on the crystalline phase of PVDF and the stretching induced chain conformation as well as ferroelectric phase transition are comprehensively disclosed. This work offers not only a fresh strategy for turning the ferroelectric performance of PVDF without the assistance of conformation stabilizing units, but also provides deeper insight into the understanding of the ferroelectric phase transition of PVDF.

Poly(vinylidene fluoride–trifluoroethylene) (P(VDF–TrFE)) has long been known for its excellent dielectric, ferroelectric and piezoelectric performances. Besides direct copolymerization of VDF and TrFE, hydrogenation of P(VDF–CTFE) has been extensively investigated to synthesize P(VDF–TrFE) for its advantages of low-cost raw materials and better controlled composition, together with mild reaction conditions. To overcome the negative influence of metal ions from the residue of catalysts on the dielectric performance of the resultant copolymers, in the present contribution, a hydrosilane catalyst system with no metal species has been reported for the hydrogenation of P(VDF–CTFE) in a controlled radical chain transfer reaction process. C–Cl bonds in CTFE are activated by silyl radicals which are in situ formed from the catalysts. The generated P(VDF–CTFE) micro-radicals would undergo a chain transfer reaction to Si–H on hydrosilane and generate new silyl radicals. The repeated chain transfer reactions between C–Cl bonds on CTFE and Si–H bonds on hydrosilane are responsible for the quantitative hydrogenation of P(VDF–CTFE) with respect to the hydrosilane dose. The low sensitivity of hydrosilane and the radical reaction pathway allow the reaction to be conducted under rather mild conditions in most of the good solvents of P(VDF–CTFE). Thanks to the metal-free feature of the catalyst, the resultant copolymer shows significantly improved dielectric performance over that catalyzed with copper complex catalysts. Reducing P(VDF–CTFE) with hydrosilane, such as (Me₃Si)₃SiH, has been demonstrated to be an environmentally friendly, controllable, metal-free and mild process to synthesize a TrFE containing fluoropolymer, which has glorious prospects for the synthesis of dielectric fluoropolymers.

Poly(vinylidene fluoride) (PVDF) based ferroelectric polymers have attracted considerable attention both academically and industrially due to their tunable ferroelectric properties. By pinning the conformation of the polymer chain and the ferroelectric phase physically or chemically, the ferroelectric behaviors of PVDF based polymers could be finely turned from normal ferroelectric into relaxor ferroelectric, anti-ferroelectric like, and even linear dielectric. Besides high energy electron irradiation and chemical copolymerization with the bulky monomers, in this work, an alternative strategy is presented to regulate the dielectric and ferroelectric performances of PVDF based ferroelectric polymer for the first time. CH=CH bonds with the desired content are inserted by a controlled dehydrofluorination reaction into a poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer (TrFE refers to trifluoroethylene) synthesized from the hydrogenation of P(VDF-CTFE) (CTFE refers to chlorothrifluoroethylene). The influence of the CH=CH bonds along with the fabrication conditions on the crystallization and ferroelectric relaxation of the resultant copolymers (referred to P(VDF-TrFE-DB)) was carefully characterized and discussed. The nonrotatable CH=CH bonds result in depressed dielectric and ferroelectric performances in the as-cast films by confining the orientation of ferroelectric grains in P(VDF-TrFE). The normal ferroelectric performance of P(VDF-TrFE) is turned into anti-ferroelectric like behavior in the resultant P(VDF-TrFE-DB). The cleavage of CH=CH bonds is responsible for the recovery of the ferroelectric behavior in the annealed samples. Uniaxial stretching favors the alignment of the polymer chain and ferroelectric domains, which may address the further regulated ferroelectric characters in the stretched samples.

A light-mediated atom transfer radical chain transfer process is proposed for the controlled hydrogenation of P(VDF-CTFE) using metal-free photocatalyst.

Poly(vinylidene fluoride) (PVDF)-based ultrafiltration membranes play key roles in aqueous separation fields. However, the inherent hydrophobicity of PVDF always generates higher water permeation resistance and a greater fouling tendency in the filtration process. Different to the widely reported and widely used blending methods of increasing the hydrophilicity of PVDF membranes, the mass-produced hydrophilic PVDF copolymer is expected to be more efficient in producing high performance membranes. For this purpose, the present research offers a new and scalable approach to improving the hydrophilic properties of PVDF-based membranes through amphiphilic copolymers. Using 2-trifluoromethylacrylic acid (MAF) and hexafluoropropylene (HFP), carboxylated PVDF (PVHM) was synthesized following simple radical suspension copolymerization. Via a non-solvent-induced phase separation (NIPS) method, PVHM membranes were prepared and characterized. It was found that the PVHM membranes had enhanced hydrophilicity, permeability, fouling resistance, and alkali resistance compared with PVDF membranes. For the PVHM containing 8.3 wt% MAF, its membrane demonstrated superior static/dynamic fouling resistance to sodium alginate (FRR up to 99.1% for SA). Therefore, carboxylated PVDF polymers show potential for use in the industrial production of high-performance ultrafiltration membranes.