PVDF-based copolymers

Electrostrictive polymers PVDF based copolymers e.g. Poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) Poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) [81... 

The most common piezoelectric polymers are PVDF, based on the monomer CH2 CF2 and copolymers of PVDF with C2F3H. Although there are many sources for materials that are nominally piezoelectric, sources for reproducible materials are limited. 

Gozdz et al. (of Bellcore) [25] recognized that poly (vinylidene difluoride) hexafluoropropylene (PVDF HFP) copolymers could form gels with organic solvents and developed an entire battery based on this concept. Typically, the gel separator is 50 pm thick and comprises 60wt. % polymer. In the Bellcore process the separator is laminated to the electrodes under pressure at elevated temperature. The use of the PVDF HFP gelling agent increases the resistivity of the electrolyte by about five times which limits the rate capability of such batteries. 

All the ordinary extrusion and molding equipment and techniques can be used to process PVDF into different shapes ranging from pipes, fitting, parts, solid rods and sheets, to thin films. Longevity of equipment can be extended using special alloys on the surface that is in contact with molten PVDF, but usually it is not necessary. PVDF based polymers are available commercially in a wide range of melt flow index and with additives to enhance processing or end use properties. However, both homopolymers and copolymers may be shaped from the molten state without extrusion aids or thermal stabilizers. 

Therefore, as Mn2(CO)io was never employed in polymerizations of main chain fluorinated monomers, or with inactivated alkyl halides or with perfluoroalkyl iodides, we decided to assess its scope and limitations as photo-coinitiator and to demonstrate that such LjjMt-MtLjj photolyzable transition metal complexes afford the initiation of VDF polymerization directly from a variety of regular and (per)fluorinated alkyl halides (Cl, Br, I) even at rt, thus opening up novel synthetic avenues for the photome-diated synthesis of block and graft copolymers based on FMs. Second, we also set to kinetically explore such polymerization and investigate the possibility of Mn2(CO)io-mediated IDT-VDF-CRP. Third, we aimed to demonstrate the first examples of the synthesis of well-defined PVDF-block copolymers. 

The electrostrictive behavior of P(VDF-CTFE) copolymers was investigated (Li et al. 2004 Li et al. 2006). A high electromechanical response was obtained in these copolymer films. As other PVDF-based polymers, the processing condition plays a very critical role on its properties. For a well-stretched and annealed P (VDF-CTFE) 88/12 copolymer film, a longitudinal electrostrictive strain as much as 5.5 % was obtained. A linear relationship between the strain response and the was observed, which indicates the electrostrictive nature of the electromechanical response in P(VDF-CTFE) copolymers. The corresponding electric field-related electrostrictive coefficient for the copolymer film is obtained as Mss = —1.23 0.02 X 10 (m /V ) (Li et al. 2006). 

As to the fabrication of PEMs, PVDF was usually used as a copolymer with hexafluoropropylene, indicated as PVDF-HFP. Kumar et al. have done much work on PVDF-HFP-based PEMs [29-33]. Since then, the copolymer was blended with other polymers or inorganic materials for ion introduction like Naflon, montmoril-lonite (MMT), and A10[0H]. Besides, PVDF has been grafted with PSSA or vinyl-imidazole (Vim) in some research works [34,35], and AI2O3, poly(ethylene glycol) (PEG), or poly(2-acrylamido-2-methyl-l-propanesulfonic acid) (PAMPS) have been used to blend with PVDF system [35,36]. In these researches, PVDF-based PEMs are designed mainly for DMFC application as well as DEFC. 

MICHAEL, M., PRABAHARANS, R.S., Rechargeable hthium battery employing a new ambient temperature hybrid polymer electrolyte based on PVK+PVdF+HFP (copolymer), J. Power Sources, 2004,136(2), 408-15. 

Technologies on PVDF based GPEs have been disclosed by Bellcore [3,4], A polymer matrix is a copolymer of vinyMene fluoride (VDF) and hexafluoro-propylene (HFP) and the LiPFg solution in EC/DMC (dimethyl carbonate) (2 1) is added to the matrix to make up a GPE of the phase separation type. HFP plays an important role in the reduction of the crystallinity of the resulting copolymer, increasing its capacity to hold the electrolyte solution. It is claimed that ionic conductivity of their GPE is almost 10 S-cm ... 

For liquid-based systems, the present state-of-the-art for commercial Li-ion batteries almost universally employs either PVDF homopolymers or PVDF-HFP copolymers for electrode binders and, in some cases, for the electrolyte separator-matrix [52]. These polymers are most effective for commercial processing of composite electrodes on current collector metal foils such as Cu and Al, and... 

The preparation and properties of a novel, commercially viable Li-ion battery based on a gel electrolyte has recently been disclosed by Bellcore (USA) [124]. The technology has, to date, been licensed to six companies and full commercial production is imminent. The polymer membrane is a copolymer based on PVdF copolymerized with hexafluoropropylene (HFP). HFP helps to decrease the crystallinity of the PVdF component, enhancing its ability to absorb liquid. Optimizing the liquid absorption ability, mechanical strength, and processability requires optimized amorphous/crystalline-phase distribution. The PVdF-HFP membrane can absorb plasticizer up to 200 percent of its original volume, especially when a pore former (fumed silica) is added. The liquid electrolyte is typically a solution of LiPF6 in 2 1 ethylene carbonate dimethyl car-... 

Mokrini, A., Huneault, M. A. and Gerard, P. 2006. Partially fluorinated proton exchange membranes based on PVDF-SEBS blends compatibilized with methylmethacrylate block copolymers. Journal of Membrane Science 283 74—83. 

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