Hexafluoropropylene Research Articles

Robust Free-standing Electrodes for Flexible Lithium-ion Batteries Prepared by a Conventional Electrode Fabrication Process

Highly flexible free-standing electrodes for flexible lithium-ion batteries (LIBs) are prepared by casting slurry on a glass substrate and detaching the film after drying. The slurry is composed of lithium cobalt oxide (LiCoO2) as a cathode material and Super-P as a conductive agent. These are currently used in conventional electrode fabricating. The flexible electrode contains the similar constituents and composition to the electrodes in commercial LIBs, but does not include metal foil as a current collector as that limits the flexibility of the LIB. Polyvinylidene fluoride (PVDF) with hexafluoropropylene (HFP) is used as a binder instead of PVDF alone due to its better mechanical properties (tensile stress, strain, and peel-off strength). In order to compensate for the low electronic conductivity of flexible electrodes without metal foil, a carbon nanotube (CNT) is incorporated into the electrode. The flexible electrodes offer great flexibility with the ability to be bent and folded without deforming. The flexible electrode exhibits high overpotential during charging/discharging process and inferior electrochemical performance (rate capability, energy density and cycling stability) to conventional electrodes with metal foil due to the low electronic conductivity but it delivers reasonable performance in a punch cell with an aluminum-deposited PET substrate as a current collector. Using CNT enhances the electrochemical properties of flexible electrodes, but weakens its mechanical strength at the same time. Therefore, the optimum amount of CNT needs to be determined.

Synthesis and characterization of poly(trifluoroethylene-co-hexafluoropropylene) and the optical properties of its thin films

Copolymers of trifluoroethylene (TrFE) and hexafluoropropylene (HFP) were synthesized and characterized by various instrumental techniques. The maximum incorporation of HFP was 19.6 mol%. It was found that the reactivity ratios of TrFE and HFP were r TrFE =4.12 and r HFP ≈0, respectively, by applying Mayo-Lewis method. It was also found that the incorporation of HFP in copolymer chain influenced thermal properties. As increasing HFP content in copolymers, the melting temperature and crystallinity of copolymers were decreased and the glass transition temperature of copolymers gradually shifted to low temperature. Reduced crystallinity of copolymers was helpful to prepare coating layers having much even surface. Compared with coating layer prepared from TrFE homopolymer, the surface roughness was decreased and light transmittance through the coating layer increased when the copolymers of TrFE and HFP were used. This tendency was more appreciable as increasing HFP content in the copolymers.

Gas permeation and diffusion in copolymers of tetrafluoroethylene and hexafluoropropylene: Effect of annealing

Two novel perfluorinated materials, copolymers of tetrafluoroethyelene (TFE) and hexafluoropropylene (HFP), were prepared and studied. In both copolymers the prevailing comonomer was HFP. The copolymers are completely amorphous and similar by their properties to poly(hexafluoropropylene) studied earlier. A detailed investigation of gas permeation parameters (permeability and diffusion coefficients) was conducted both at ambient temperature and in the range 22–50°C. For comparison, additional measurements of temperature dependencies of transport parameters were performed for annealed films of poly(hexafluoropropylene). On the Robeson diagrams for gas pairs He/H2, He/CH4 the data points of the ‘as cast’ films of the copolymers were located between Upper Bounds (UB) of 1991 and 2008. However, annealing of the copolymers resulted in a dramatic increase in selectivity, so the data points shifted above UB-2008 on these diagrams as well on those for the gas pairs H2/CH4, N2/CH4 and He/N2. This makes these copolymers interesting candidates for separation gas mixtures containing He and H2.

A closer look at the reactivity between N-heterocyclic carbenes and fluoroalkenes

The fundamental reactivity leading to N-heterocyclic fluoroalkene adducts is explored in detail, featuring a total of 15 N-heterocyclic carbenes (NHCs) with various electronic and steric environments. The activity of these carbenes towards tetrafluoroethylene (TFE), hexafluoropropene (HFP), trifluoroethylene (HTFE) and vinylidene fluoride (VDF) is assessed in THF and toluene. Attempts were made to correlate the observed reactivity with electronic (Tolman Electronic Parameters) and steric (% buried volume) parameters unique to each NHC, but a trend has yet to be fully determined. However, the unique steric constraints of a cyclic (alkyl)(amino)carbene (CAAC) were shown to modify the initial point of nucleophilic attack on HTFE, providing selective transformation to a different adduct than has been observed to date with all reactions involving this fluoroalkene.

Temperature and pressure effects on the product distribution of PTFE pyrolysis by means of qualitative, in-line FTIR analysis

The results of the depolymerisation of PTFE under steady operating conditions in a semi-automated, continuous depolymerisation system are presented. The influence of temperature and pressure on the selectivity of the three main products of depolymerisation (tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and octafluorocyclobutane (OFCB)) was investigated via qualitative in-line FTIR analysis. No carrier gas was used, with the PTFE feed rate and experimental run time kept constant. The temperature and pressure ranges investigated were: 650 °C–750 °C and <10 kPa–40 kPa. The optimum operating conditions to maximise the three main products were determined using response surface methodology following a three-level face centered composite design. A TFE mole fraction of 0.95 and higher was achieved at operating conditions of ±675 °C and <10 kPa. HFP mole fractions of 0.19 and higher were achieved within the operating range of 744 °C–750 °C and 32 kPa up to 40 kPa. At operating conditions of 750 °C and 40 kPa, OFCB fractions of 0.5–0.55 were achieved. The OFCB and HFP mole fractions achieved differed from those previously mentioned in the literature. Analysis of the determined product specific kinetics indicates that the predominant HFP production pathway at low residence times (<3 s) is via the reaction of TFE with difluorocarbenes. At higher residence times the dominant reaction pathway is the dissociation OFCB.

On the Limits of Sensitivity of PALS to Incorporated Free Volume Holes in Polymeric Membranes and Sorbents: Effect of &lt;i&gt;sc&lt;/i&gt;-CO&lt;sub&gt;2&lt;/sub&gt; in Polyhexafluoropropylene

Positron annihilation lifetime spectroscopy (PALS) is a recognized instrument for the studies of size-distribution of nanopores (intrinsic free volume holes FVH) in polymers, particularly membrane materials. The limits of this application in the case of “alien” pores, produced by swelling of poly (hexafluoro propylene) PHFP in the gas (CO2) in super-critical (sc-) state are discussed. The obtained conclusions are controlled by measurements of low temperature gas (N2) sorption (LTGS) and by comparison of the data with the results on permeation of various gases through the PHFP membrane. Attention is payed to relaxation with time of the newly created FVH in the PHFP membrane.

Tuning hydrophobicity of a fluorinated terpolymer in differently assembled thin films

In the current report, casting from good solvent (acetone) and casting from mixed solvent and nonsolvent were employed for preparing thin films of terpolymer of Tetrafluoroethylene (TFE), Hexafluoropropylene (HFP), and Vinylidene fluoride (VDF) (THV), on silicon wafers. These films revealed various morphologies and wetting behaviors depending on the solution concentration, temperature, and thin film preparation method. The THV thin films prepared by casting from good solvent showed smooth morphology with holes. The thin film prepared from a 3 wt % THV/acetone solution by casting from good solvent at 15 °C demonstrated spheres in addition to the smooth morphology, while the thin film prepared from a 5 wt % THV/acetone solution at 15 °C by casting from good solvent had a mesh-like structure with some linked spheres. Casting the thin films from mixed solvent and nonsolvent resulted in various morphologies such as different sphere sizes embedded in a dense film layer, and hexagonal close packed structures. The thin films prepared by casting from good solvent showed a slightly hydrophobic character, with a measured water contact angle of approximately 99°, while the nonsolvent cast films had a water contact angle as high as 145°. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 643–657

Design of a continuous gas-phase process for the production of hexafluoropropene oxide

The partial oxidation of hexafluoropropene (HFP) yields 2,2,3-trifluoro-3-trifluoromethyl oxirane (commonly known as hexafluoropropene oxide, HFPO), a highly reactive and versatile fluorochemical intermediate that is used in the manufacture of various high-performance organofluorine products. Most industrial methods of HFPO preparation involve the high-pressure liquid-phase oxidation of HFP in the presence of chemical oxidizers and solvents. Processes that employ molecular oxygen as the oxidizing agent generally have a lower environmental impact. In this study, the design and analysis of a 500tpa continuous gas-phase process for the epoxidation of HFP with molecular oxygen was carried out. A modular coil-type reactor fabricated from drawn copper tubing is proposed to attain residence times up to 120s which are required for acceptable levels of HFP conversion (70%) and HFPO yield (40%). The HFPO product is separated from the residual HFP through a novel sequence of CO2 gas stripping and conventional distillation steps. A final product having a purity of 99.8mol% is obtained. The recovered HFP, which has a purity of 99.2mol%, is subsequently recycled. The process unit operates at a HFP recycle ratio of 0.39.

Influence of barium titanate nanofiller on PEO/PVdF-HFP blend-based polymer electrolyte membrane for Li-battery applications

Organic-inorganic hybrid membranes based on poly(ethylene oxide) (PEO) 6.25 wt%/poly(vinylidene fluoride hexa fluoro propylene) [P(VdF-HFP)] 18.75 wt% were prepared by using various concentration of nanosized barium titanate (BaTiO3) filler. Structural characterizations were made by X-ray diffraction and Fourier transform infrared spectroscopy, which indicate the inclusion of BaTiO3 in to the polymer matrix. Addition of filler creates an effective route of polymer-filler interface and promotes the ionic conductivity of the membranes. From the ionic conductivity results, 6 wt% of BaTiO3-incorporated composite polymer electrolyte (CPE) showed the highest ionic conductivity (6 × 10−3 Scm−1 at room temperature). It is found that the filler content above 6 wt% rendered the membranes less conducting. Morphological images reveal that the ceramic filler was embedded over the membrane. Thermogravimetric and differential thermal analysis (TG-DTA) of the CPE sample with 6 wt% of the BaTiO3 shows high thermal stability. Electrochemical performance of the composite polymer electrolyte was studied in LiFePO4/CPE/Li coin cell. Charge-discharge cycle has been performed for the film exhibiting higher conductivity. These properties of the nanocomposite electrolyte are suitable for Li-batteries.

Gel P (VdF/HFP) / PVAc / lithium hexafluorophosphate composite electrolyte containing nano ZnO filler for lithium ion batteries application: Effect of nano filler concentration on structure, thermal stability and transport properties

Nano ZnO filler incorporating gel co-polymer composites electrolytes membranes were prepared using a solution cast technique. All prepared membranes were characterized using different techniques such as X-ray diffraction (XRD), thermal analysis (TG, DSC), Fourier transform infra –red spectroscopy (FT-IR) and scanning electron microscopy (SEM). X-ray diffraction analysis showed the effect of lithium hexafluorophosphate (LiPF6), poly vinyl acetate (PVAc) and nano zinc oxide (ZnO) on the crystalline structure of the polyvinylidene fluoride –co– hexafluoro propylene (PVdF-co-HFP) matrix containing ethylene carbonate (EC) and diethyl carbonate (DEC) as plasticizers. FT-IR analysis confirmed the good dissolution of the LiPF6 salt and the good interaction of the nano ZnO filler with the co-polymer matrix. TG analysis showed the good thermal stability of the samples containing ZnO compared to the free one. Also, addition of nano ZnO filler enhanced the conductivity value of the co-polymer composites electrolytes. The sample containing 6 wt % of ZnO delivered the highest conductivity value of about 3.69 × 10−4 Ω−1 cm−1 at room temperature with a good thermal stability behavior (Td = 325 °C).

Experimentally Calibrated Random Walk of Branched Polymers: A Pragmatic Approach

In order to control the branching behavior of polymers, the comparison of experimental and simulated data is important. The utilization of a nonlattice, self‐avoiding necklace‐bead random walk simulator is reported, which allows for the calculation of radii of gyration r g of polymer molecules with branched structures. The focus is on sensitivity toward short‐chain branches, long‐chain branches (LCBs), and the copolymer composition. Using only two parameters—the size of monomer beads and the minimum angle between three subsequent beads—a fast and reliable parameter fit procedure based on experimental data is described. The procedure is exemplarily shown for copolymers of vinylidene fluoride and hexafluoropropene (HFP) with HFP contents in the copolymer of at most 0.3 and is easily transferable to other polymers that may be analyzed by size‐exclusion chromatography/multiangle laser light scattering close to θ conditions. Applying the Zimm–Stockmayer equation to simulated r g data allows for comparing the “effective” number of LCBs with the number of LCBs given by kinetic simulations. A tool for better estimation of rate coefficients associated with the formation of short‐ and long‐chain branches is provided.image

Nano lithium aluminate filler incorporating gel lithium triflate polymer composite: Preparation, characterization and application as an electrolyte in lithium ion batteries

Gel polymer composites electrolytes containing nano LiAlO2 as filler were prepared using a solution cast technique and characterized using different techniques such as X-ray diffraction (XRD), thermal analysis (TG, DSC), Fourier transform infra – red spectroscopy (FT-IR) and scanning electron microscope (SEM). X-ray diffraction analysis showed the effect of lithium tri fluoro methane sulphonate (LiCF3SO3), poly vinyl acetate (PVAc) and nano lithium aluminate (LiAlO2) on the crystalline structure of the poly vinylidene fluoride –co– hexa fluoro propylene (PVDF-co-HFP) matrix containing ethylene carbonate (EC) and diethyl carbonate (DEC) as plasticizers. FT-IR analysis confirmed both the good dissolution of the LiCF3SO3 salt and the good interaction of the nano LiAlO2 filler with the polymer matrix. TG analysis showed the good thermal stability of the LiAlO2 samples compared to the free one. Also, addition of nano LiAlO2 filler enhanced the conductivity value of the polymer composites electrolytes. The sample containing 2 wt% of LiAlO2 showed the highest conductivity value, 4.98 × 10−3 Ω −1 cm−1 at room temperature, with good thermal stability behavior (Td = 362 °C). This good conductive and thermally stable polymer nano composite electrolyte was evaluated as a promising membrane for lithium ion batteries application.

First-principles simulations of PVDF copolymers with high dielectric energy density: PVDF-HFP and PVDF-BTFE

Phase diagrams of polyvinylidene fluoride (PVDF) and its copolymers with hexafluoropropylene (HFP) and bromotrifluoroethylene (BTFE) are investigated via first-principles simulations and compared to previously studied P(VDF-chlorotrifluoroethylene) (CTFE) data. We find that a nonpolar to polar phase transition induced by an electric field also occurs in HFP and BTFE copolymers and the results for P(VDF-HFP) show good agreement with existing experiments. For P(VDF-BTFE) we show that its nonpolar phase remains the ground state for a substantially larger range of concentrations than for P(VDF-CTFE) and P(VDF-HFP), and predict that a high BTFE concentration copolymer will achieve a significantly higher energy density at low field than P(VDF-CTFE) 9%. The transition pathways connecting the polar and nonpolar phases are also calculated and the energy barriers for the transitions turn out to be similar for the three copolymers, even at different co-monomer concentrations. The similarity of barriers indicates that a mixture of these and related copolymers can be used to optimize the properties of the dielectric, such as energy density, processability, and cost.

ChemInform Abstract: Direct Isoperfluoropropylation of Arenediazonium Salts with Hexafluoropropylene.

An efficient copper-promoted isoperfluoropropylation of aryl diazonium salts is described. The reaction occurs under mild conditions using commercially available hexafluoropropylene (HFP) as the starting material. In addition, a one-pot direct diazotization and isoperfluoropropylation protocol was developed. The method allows facile conversion of various arylamines into isoperfluoropropylarenes with good functional group compatibility using HFP.

Direct heptafluoroisopropylation of arylboronic acids via hexafluoropropene (HFP).

A novel and straightforward strategy for heptafluoroisopropylation of arylboronic acids at room temperature has been developed. This method, directly using commercial available hexafluoropropene (HFP) as the starting material, provides a new way to synthesize a variety of synthetically useful heptafluoroisopropylated arenes.

Studies on oligomerization and kinetic of pyrolyzing trifluoromethane to tetrafluoroethylene and hexafluoropropylene

The pyrolysis experiment of trifluoromethane (R23) to tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) was carried out in a nickel tubular reactor at temperature of 700–900°C and residence time of 4–40s. Gas products were identified as TFE, C3F8, C2HF5, HFP, CF3CCCF3, CF2CHCF3, cyc-C4F8, CF3CFCFCF3, n-C4F10, CF2CFCF2CF3, CF2C(CF3)2 (PFiB), CH(CF3)3 and cyc-C5F10 by using GC–MS. It was proposed that TFE and HFP would convert into oligomers at high temperature and long residence time through elemental balance analysis and formation rate measurement of HF and oligomers. Oligomers formed during pyrolysis reaction was also analyzed by 1H NMR method. Based on the studies of oligomerization and reported papers, a relatively detailed pyrolysis mechanism and kinetic model was developed. The results revealed that the molecular structure of oligomers was only consist of carbon and fluorine element and could be expressed as (CF2)n. The computer simulation result of kinetic model showed good agreement with experimental data as the deviation of model was acceptable.

Simultaneous determination of three organic fluorides in workplace air by portable gas chromatography-mass spectrometer

To establish a method for rapid determination of organic fluorides in the air of a fluorine chemical plant using portable gas chromatography-mass spectrometer (GC-MS). Standard samples of monochlorodifluoromethane, tetrafluoroethylene, and hexafluoropropylene of different concentrations were prepared by static volumetric method with high-purity nitrogen as the diluent gas. The samples were injected into the GC-MS by a hand-held probe. Retention time and characteristic ion were used for qualitative analysis, and the area of selected ion peak was used for quantitative analysis. The standard curves were then created for quantitative determination of the three organic fluorides. The linear ranges for monochlorodifluoromethane, tetrafluoroethylene, and hexafluoropropylene by the method were 0.39-7.72, 0.45-8.84, and 0.61-12.20 mg/m3, respectively, the average recovery rates for the three concentrations were 102.8%, 96.0%, and 106.5%, respectively, and the average deviations were 2.1%, 5.1%, and 2.4%, respectively. The portable GC-MS can be used for the simultaneous qualitative and quantitative analysis of monochlorodifluoromethane, tetrafluoroethylene, and hexafluoropropylene in the workplace air, and the method is simple, fast, and accurate.

Multidimensional 19F NMR Analyses of Terpolymers from Vinylidene Fluoride (VDF)–Hexafluoropropylene (HFP)–Tetrafluoroethylene (TFE)

The use of multidimensional NMR methods for the characterization of polymer microstructure has been applied to terpolymers from vinylidene fluoride (VDF), hexafluoropropylene (HFP), and tetrafluoroethylene (TFE). By assembling the atomic connectivity information obtained from different multidimensional NMR experiments, selective 19F–19F COSY (correlation spectroscopy), 19F–19F gradient double-quantum COSY, and 19F–13C gradient heteronuclear single-quantum coherence (gHSQC), among others, the detailed monomer sequence arrangements in the terpolymer were obtained. Obtaining the resonance assignments of the terpolymer was greatly aided by the extrapolation of known resonance assignments from PVDF homopolymer, poly(VDF-co-HFP) copolymer, and poly(VDF-co-TFE) copolymer. A tabulated comparison of the microstructure assignment of resonances from PVDF homopolymer as well as poly(VDF-co-HFP) and poly(VDF-co-TFE) copolymers and the terpolymer is provided. Detailed comparisons of 19F spectra from 470 and 658.4 MHz spectrometers, revealing the AB patterns present in this terpolymer, are presented and discussed in this paper. The compositions of the comonomers in the terpolymers were calculated with different methods, all of which gave similar values. The percentages of VDF and HFP monomer inversions in the terpolymers were also calculated from the assigned NMR resonances.

Preparation, zinc ion transport properties, and battery application based on poly(vinilydene fluoride-co-hexa fluoro propylene) polymer electrolyte system containing titanium dioxide nanofiller

New nanocomposite polymer electrolytes have been synthesized by solution casting technique with a view to investigate detailed transport characteristics of a zinc (Zn2+) ion-conducting polymer electrolyte system, namely, poly(vinilydene fluoride-co-hexafluoropropylene):zinc triflate in the ratio of 75:25 dispersed with 1, 3, 5, 7, and 10 wt% titanium dioxide (TiO2) nanofiller, respectively. The particular polymer electrolyte specimen having 5 wt% TiO2 nanofiller exhibited the maximum electrical conductivity of 3.4 × 10−4 S cm−1 at room temperature (298 K). Frequency response analysis in terms of conductivity and dielectric relaxation studies has been carried out in order to ascertain the possible movement of ions within the polymer matrix. The modulus spectra show the existence of a non-Debye type of relaxation occurring with a distribution of relaxation times. The Zn2+ ionic transport number has been determined to be approximately 0.57, thereby suggesting the predominant impact of Zn2+ ions toward the measured total electrical conductivity. Differential scanning calorimetric results have confirmed that with the loading of TiO2 nanofiller up to 5 wt%, glass transition temperature and degree of crystallinity of the polymer decrease but increase slightly beyond 5 wt% TiO2. The present X-ray diffraction analysis has revealed the occurrence of ion/filler interactions within the polymer network due to the dispersion of TiO2 nanofiller. Certain device characteristics have also been evaluated by fabricating an appropriate electrochemical cell based on Zn/manganese dioxide electrode couple as an area of application and examining relevant discharge features.

Characterization and quantification of microstructures of a fluorinated terpolymer by both homonuclear and heteronuclear two-dimensional NMR spectroscopy.

Fluoropolymers are usually insoluble in organic solvents. Insolubility of fluoropolymers limits basic characterization such as microstructural investigations. In the family of fluoropolymers, terpolymer of tetrafluorethylene (TFE), hexafluoropropylene (HFP), and vinylidene fluoride (VDF), named THV is one of the newest members. There are nine grades of THV available. Among the nine grades, THV-221 G is an ideal model polymer for basic characterization purposes. THV-221 G is soluble in solvents such as acetone and ethyl acetate. In the current report, both homonuclear and heteronuclear 2D NMR experiments were employed in solution on THV-221 G. The homonuclear gradient correlation spectroscopy NMR measurement revealed that THV has two adjacent TFE units in addition to TFE-HFP sequence orders. The fraction of the microstructures is quantified by the analysis of 1D solution (19)F NMR spectrum. Further, the gradient heteronuclear single quantum coherence experiment helped with the clarification of chemical environments of the units TFE, HFP, and VDF. The 1D solution (13)C NMR spectrum was helpful in clarifying sequence assignments of VDF. It is concluded that THV is a random polymer with a limited fraction of TFE-TFE and TFE-HFP sequence orders in addition to head-to-tail polymerization of VDF unit.