Copolymer Of Tetrafluoroethylene Research Articles

Influence of third monomer on the crystal phase transition behavior of ethylene–tetrafluoroethylene copolymer

Crystal phase transition between the low- and high-temperature phases has been investigated for ethylene (E)–tetrafluoroethylene (TFE) alternating copolymer (ETFE) containing the third monomeric species by the temperature dependent measurements of wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) and differential scanning calorimetry. Nonafluoro-1-hexene (NFH) and hexafluoropropylene (HFP) were chosen as the third monomers, where they are different in the side-branch length, –(CF2)3CF3 and –CF3, respectively. In the case of E/TFE/NFH copolymer (ET–C4F9), the crystal phase transition temperature of the original ETFE two-components copolymer was not very much affected by the existence of NFH in the range of NFH content from 0.7 to 3mol%. Contrarily, the crystal phase transition temperature of E/TFE/HFP copolymer (ET–CF3) was found to decrease drastically with increasing HFP content. The melting temperature and the higher-order structure were also affected sensitively depending on the HFP content. This difference in phase transition behavior between ET–C4F9 and ET–CF3 copolymers is reasonably interpreted as follows: the short side groups (–CF3) of HFP monomeric unit are included in the crystal lattice of E/TFE chains and the unit cell is expanded gradually with an increment of the HFP content, resulting in the decrease in phase transition point because of easier thermal motion of the chains. On the other hand, the long side groups [–(CF2)3CF3] of NFH monomeric units are excluded out of the crystal lattice and located on the lamellar surfaces or in the amorphous region and do not affect very much the phase transition temperature even when the NFH content is increased. In association with such a change in crystal structure, the long period of stacked lamellar structure was found to decrease remarkably in the case of NFH, whereas it does not change very much for HFP, consistent with the interpretation of the above-mentioned WAXD data.

The thermal desorption mass spectra of polytetrafluoroethylene modified under the action of radiation at elevated temperatures

The products of the pyrolysis of polytetrafluoroethylene (PTFE) in a vacuum modified under the action of gamma irradiation in the molten state were studied mass spectrometrically at various temperatures. Radiation modification was found to cause the appearance of an additional stage of the thermal decomposition of PTFE at decreased temperatures compared with not irradiated PTFE. The chemical composition of the gas components of thermal decomposition substantially changes after the irradiation of PTFE, which increases the molecular weight of decomposition products. A comparison with the results of an additional study of the thermal decomposition of tetrafluoroethylene copolymer with hexafluoropropylene is evidence of the formation of side CF3 groups in PTFE under irradiation. Data on the composition of gaseous products of PTFE radiolysis under gamma irradiation were obtained.

Structural study of a series of ethylene–tetrafluoroethylene copolymers with various ethylene contents, Part 2: Phase transition behavior investigated by temperature dependent measurements of X-ray fiber diagrams

Phase transitional behavior has been investigated for a series of ethylene (E) and tetrafluoroethylene (TFE) two-component copolymers on the basis of the temperature dependent measurement of X-ray fiber diagrams taken for the uniaxially-oriented samples. The usage of such uniaxially-oriented samples has allowed us to clarify the structural changes more definitely than before. So far, the crystalline transition from the low-temperature phase to the high-temperature phase had been assumed to occur continuously, but the detailed analysis of the X-ray reflections at higher scattering angles revealed for the first time that the transition is of the thermodynamically-discontinuous first-order type between the monoclinic and the pseudohexagonal phases. This phase transition temperature shifted toward lower temperature side as the TFE content became higher. The analysis of the X-ray reflection profile allowed us to imagine that low-temperature shift of the transition point is considered to occur due to the easier thermal motion of the planar-zigzag chains around the chain axis because of looser packing of chains containing higher population of bulky CF2CF2 groups. From these experimental data a phase diagram has been built up to show the phase transition behaviors of a series of E/TFE copolymers in a systematic manner. The characteristic features of the structural disordering including trans–gauche conformational exchange have been also discussed on the basis of the data of polarized infrared and Raman spectra combined with the X-ray diffuse scatterings.

Temperature Dependence of the Free Volume in Amorphous Teflon AF1600 and AF2400: A Pressure−Volume−Temperature and Positron Lifetime Study

The microstructure of the free volume and its temperature dependence were studied for amorphous Teflon AFs using pressure−volume−temperature experiments (PVT) and positron annihilation lifetime spectroscopy (PALS). Two copolymers of tetrafluoroethylene and 2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole units with a composition of 35:65 (AF 1600, Tg = 160 °C) and 13:87 mol parts (AF 2400, Tg = 240 °C) were investigated after drying the as-received materials. The results are compared with those for CYTOP (Tg = 105 °C) and the perfluoroelastomer PFE (Tg = −2 °C) as well as for conventional (non-fluorinated) polymers. The PVT data were fitted by the Tait equation and the Simha−Somcynsky (S−S) equation of state (eos). From the latter one the hole fraction h and the specific hole free volume, Vf = hV, were determined. From the PALS data published recently by some of the authors (Rudel et al. Macromolecules 2008, 41, 788) the free volume hole size distribution characterized by its mean, ⟨vh⟩, and standard dev...

Positron and Positronium Annihilation in Polymers Studied by Age-Momentum Correlation Spectroscopy

Positron (e) and positronium (Ps) annihilation processes in polymers are studied by positron age-momentum correlation spectroscopy, which can sensitively probe momentum distributions of e, p-Ps, and o-Ps. For polyether sulfone and ethylene tetrafluoroethylene copolymer belonging to oxygen-containing polymers (O group) and fluorine-containing polymers (F group), respectively, significant effects of positron trapping by polar element are observed. The Doppler profile of o-Ps pick-off annihilation is strongly influenced by F atoms, giving rise to anomalous broadening. The results are discussed together with our previous data of the S−I3 correlation in order to explore the feasibility of chemical analysis around the free volumes by age-momentum correlation spectroscopy.

Gated proton transport in aligned mesoporous silica films

Modulated proton transport plays significant roles in biological processes such as ATP synthesis as well as in technologically important applications including, for example, hydrogen fuel cells. The state-of-the-art proton-exchange membrane is the sulphonated tetrafluoroethylene copolymer Nafion developed by DuPont in the late 1960s, with a high proton conductivity. However, actively switchable proton conduction, a functional mimic of the ion transport within a cell membrane, has yet to be realized. Herein, we report the electrostatic gating of proton transport within aligned mesoporous silica thin film. It is observed that surface-charge-mediated transport is dominant at low proton concentrations. We have further demonstrated that the proton conduction can be actively modulated by two-fourfold with a gate voltage as low as 1 V. Such artificial gatable ion transport media could have potential applications in nanofluidic chemical processors, biomolecular separation and electrochemical energy conversion.

Morphology of polyvinylidenefluoride and the copolymer of tetrafluoroethylene with ethylene using thermomechanical analysis

AbstractThe morphology of polyvinylidenefluoride (PVDF) and the copolymer of tetrafluoroethylene with ethylene (CTE) were investigated by thermomechanical analysis. Both granules and highly dispersed powders of the polymers have similar morphology. Polymer granules contain amorphous and crystalline regions. The morphology of the polymer powders were determined under two analytical conditions: coaxial, when the vectors of polymer loading and vector of compression pressure are in the same plane, or when they are perpendicular to each other. One amorphous and two crystal blocks were found at coaxial orientations of the vectors. Thermomechanical analysis showed that the polymers had a completely amorphous diblock morphology at the perpendicular orientation of the vectors. Parameters that characterize a degree of interchain interaction, such as coefficients of thermal expansion, free volume, and temperatures of polymer transformation into the glassy, high‐elastic, or flow‐viscous state were determined. PVDF and CTE have similar topographic composition, but different molecular mass and temperatures of phase transitions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Improvement of thermoluminescent sheet for a two-dimensional dosimetry system

We developed a two-dimensional dosimetry system with a thermoluminescent (TL) sheet prepared from a mixture of LiF:Mg,Cu,P (NTL-250, Nemoto) and a copolymer of ethylene and tetrafluoroethylene (ETFE). The tissue-equivalent property of the TL sheet and a dosimetry system with the sheet were presented at the last conference (SSD14). However, the system left room for improvement in thermostability. In this paper, we review our investigation intending to reveal the causes of thermal problems, the sensitivity loss of LiF:Mg,Cu,P, and the softening of the TL sheet below the melting point of the binder material, and to produce a prototype of a modified TL sheet with better thermostability.

Pentacene Field-Effect Transistor with Ferroelectric Gate Insulator as Maxwell–Wagner Effect Element

The behavior of charges in pentacene field-effect transistors (FETs) with a ferroelectric gate insulator [copolymer of vinylidene fluoride and tetrafluoroethylene, i.e., P(VDF-TeFE)] was investigated. Two peaks appeared in the Igs–Vgs characteristics at Vds = 0 V. Analyzing the behavior of the charges in the pentacene FETs revealed that the first peak appearing at the lower Vgs is ascribed to the exhaustion of accumulated holes at the pentacene/P(VDF-TeFE) interface in the direction from the interface to the source and drain electrodes in response to the electric field formed in pentacene. On the other hand, the second peak appearing at the higher Vgs is ascribed to the turn-over of the spontaneous polarization of the P(VDF-TeFE). However, a threshold voltage shift due to the spontaneous polarization that was small compared with the expected shift suggests that the turn-over of the spontaneous polarization is partial. A mechanism of the turn-over of spontaneous polarization is analyzed in terms of the Maxwell–Wagner effect.

Structural study of a series of ethylene–tetrafluoroethylene copolymers with various ethylene contents, Part 1: Structure at room temperature investigated for uniaxially-oriented samples by an organized combination of 2D-WAXD/SAXS and IR/Raman spectra

The X-ray fiber diagrams, polarized infrared/Raman spectra, and small-angle X-ray scattering data have been successfully measured for a series of uniaxially-oriented ethylene (E)–tetrafluoroethylene (TFE) random copolymers. The difference in crystal structure and morphology has been investigated. All the samples of E/TFE copolymer were found to take the planar-zigzag conformation at room temperature except pure polytetrafluoroethylene case. The layer line intensities of the X-ray fiber diagram and the 00l reflection intensities were found to change systematically. From this, the E and TFE sequences were considered to be included commonly in a crystal lattice. The detailed investigation of the polarized infrared and Raman spectra allowed us to assign the bands to some characteristic structures. These can be used effectively in the study of structural changes occurring in the phase transition of these copolymer samples. The 2-dimensional small-angle X-ray scattering patterns were compared among the copolymers and the difference in stacked lamellar structure has been discussed.

Ultrafast Chemistry of Nanoenergetic Materials Studied by Time-Resolved Infrared Spectroscopy: Aluminum Nanoparticles in Teflon

Ultrafast mid-infrared (IR) spectroscopy is used to monitor chemical reactions initiated by flash-heating a nanoenergetic material consisting of 30 nm diameter Al nanoparticle fuel in a TeflonAF oxidizer. TeflonAF is a copolymer of tetrafluoroethylene (TFE) and 2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole (dioxole), so Al can react with several different moieties. Transitions associated with CF2 stretching of TFE or CFO stretching or CF3 stretching of dioxole were monitored. The reactions of Al with CFO occurred with time constant (k1)-1 = 50 (±20 ps); reactions of Al with CF2 or CF3 were more than 10 times slower, (k2)-1 = 0.7 (±0.05 ns). An interesting frequency oscillation is seen in the 1148 cm-1 band, where the peak frequency undergoes a time-dependent shift from 1148 to 1155 cm-1 and then back to 1148 cm-1. Due to the coincidence of CFO and CF2 stretching transitions, this band in the copolymer represents an amalgamated vibration with amplitude on both TFE and dioxole. As concentration is varie...

Gas solubility and permeability in MFA

AbstractAn experimental analysis has been performed in this work, aimed to the characterization of thermodynamic and mass transport properties of a semicrystalline fluoro polymer (MFA) obtained from the copolymerization of tetrafluoroethylene (TFE) and perfluoromethylvinylether. Sorption and permeation experiments for two alkanes and corresponding perfluorinated compounds in MFA were performed at two different temperatures and solubility coefficients, as well as diffusivity and permeability, were determined. Experimental data were analyzed through different thermodynamic models to draw general conclusions about properties of MFA polymeric phases. Special attention was devoted to the glassy nature of MFA polymeric mixtures around room temperature. Indeed, analysis of experimental sorption data was performed through the use of specific models for glassy polymeric phases as well as by means of classical equilibrium models for fluid mixtures. Conclusions have been drawn from the aforementioned analysis, which significantly contributes to the discussion of correct location of glass‐transition temperature for PTFE and its copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1637–1652, 2007

Polymer–LiF: Mg,Cu,P foil as thermoluminescent detector of low-energy X-rays

Thermoluminescent responses of LiF: Mg,Cu,P and co-polymer of tetrafluoroethylene and ethylene (ETFE) dosimeters exposed to low-energy X-rays from 0.6 to 8.1 keV are compared with responses of TLD-700H. Thickness of a front dead layer of ETFE, which screens the LiF: Mg,Cu,P grains, is estimated with the use of a narrow band of 1.1-keV radiation emitted from Xe/He plasma generated with a laser beam. Absorption properties of the polymer–LiF: Mg,Cu,P dosimeters are measured with 5.9-keV radiation. A large area polymer–LiF: Mg,Cu,P dosimeter is presented as a recording full cross-section of a beam of Cu - K α radiation (8050 eV) from a copper rotating anode. The surface roughness of polymer–LiF: Mg,Cu,P dosimeters is compared with the roughness of TLD chips.

Modeling of the Homogeneous Free‐Radical Copolymerization Kinetics of Fluoromonomers in Carbon Dioxide at Supercritical Conditions

Simulations of the free‐radical homopolymerization and copolymerization kinetics of fluoromonomers in carbon dioxide at supercritical conditions are presented. The homogeneous homopolymerization of dihydroperfluorooctyl acrylate (FOA) and the surfactant‐free precipitation copolymerization of tetrafluoroethylene (TFE) with vinyl acetate (VAc) in supercritical carbon dioxide were used as case studies. Reasonable agreement between experimental data from the literature and model predictions of monomer conversion vs. time, number and weight average molecular weights vs. conversion, and copolymer composition vs. conversion, for the above mentioned systems, was obtained.

Comparison of Hydrogen Sulfide Transport Properties in Fluorinated and Nonfluorinated Polymers

Permeability coefficients of hydrogen sulfide in fluorinated polymers are anomalously low when compared to its permeability in nonfluorinated polymers. As a result, fluoropolymer membranes have unusual selectivities for gas pairs involving H2S. For example, while the mixture CO2/H2S selectivity is 0.66 for nonfluorinated, rubbery poly(dimethylsiloxane), this selectivity is 8.0 for a fluoroelastomer composed of tetrafluoroethylene, perfluoromethyl vinyl ether, and perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene (TFE/PMVE/8CNVE) and 27 for a glassy, cyclic perfluoroether (Cytop) under similar test conditions. The low H2S permeability in fluoropolymers is caused primarily by unexpectedly low H2S solubility in the fluorinated polymer matrices. For instance, H2S solubility in a Teflon AF copolymer of tetrafluoroethylene and 2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole is approximately 5 times lower than the value predicted by a correlation of solubility with gas critical temperature. This low solubility is ...

Low-temperature fluorination of fluoro-containing polymers: EPR studies of polyvinylidenefluoride and the copolymer of tetrafluoroethylene with ethylene

The direct fluorination of polyvinylidenefluoride (PVDF) and the copolymer of tetrafluoroethylene with ethylene (CTE) was studied at 35–300 K. The dependence of radical formation on temperature and reaction time was obtained by use of electron paramagnetic resonance (EPR) spectroscopy. Primary alkyl radicals formed as a result of the reaction of fluorine abstracting a hydrogen from the polymer were detected at 35 K. These radicals rapidly react with molecular oxygen producing long-lived (∼48 h at 300 K) peroxy radicals. The peroxy radicals when subjected to UV-irradiation ( λ < 280 nm) give rise to other radicals that are not stable at T > 77 K. The concentration of the radicals produced during fluorination of PVDF at 77–200 K is one order of magnitude less than that formed from CTE under similar conditions. A mechanism based on the abstraction of the H and the energies of the C–H bonds is given. Density functional theory was used to predict the structures and EPR parameters for a number of fluorinated radicals to explain the observed spectra. The FOO radical was detected at low temperatures.

New Amorphous Fluoropolymers of Tetrafluoroethylene with Fluorinated and Non-Fluorinated Tricyclononenes. Semiconductor Photoresists for Imaging at 157 and 193 nm

Twenty-two tricyclo[4.2.1.02,5]non-7-ene (TCN) or 3-oxatricyclononene monomers, having fluorinated or nonfluorinated substituents on the four-membered rings, were prepared by cycloaddition reactions of functionalized olefins with norbornadiene or quadricyclane. Radical polymerizations with tetrafluoroethylene (TFE) and/or TFE and acrylates provided amorphous polymers with high solubility in standard organic solvents. The TFE/TCN dipolymers typically have glass transition temperatures of over 200 °C, substantially higher than TFE copolymers with norbornene. Perfluoroalkyl sulfonyl fluoride groups can be incorporated in the side chains of the TCN monomers giving soluble copolymers. Polymers which also incorporated acrylate monomers were prepared using a semibatch process to control composition. Selected polymers incorporating tertiary alkyl ester groups from the TCN monomer or acrylates have shown good image formation when compounded with a photoacid generator, imaged with 157 or 193 nm light, and developed using aqueous base.

Final thermally stimulated discharge current in nonpolar materials

The final thermally stimulated discharge current technique is used to study the molecular movements in nonpolar dielectrics. The main peak is an apparent peak being very sensitive to the experimental conditions. The experimental conditions can be chosen so that the thermal activation energy W, a characteristic parameter which has to be independent of the experimental conditions, can be determined. Five relaxations have been identified for Teflon FEP (a copolymer of tetrafluoroethylene with hexafluoropropylene) in the temperature range from 30to320K. W is in the range from 0.06to0.53eV.

Hyflon Ion Membranes for Fuel Cells

Processes based on membranes are attracting growing interest in the scientific community and in industry, because, in many cases, they offer a favorable alternative that is not easily achievable using conventional routes. In particular, membranes made with perfluorinated polymers are very interesting, because they exhibit unique features. Hydrophilic highly conductive proton exchange membranes have been developed from the copolymer of tetrafluoroethylene (TFE) and a short-side-chain (SSC) perfluorosulfonylfluoridevinyl ether (Hyflon Ion); they have found interesting application in the field of fuel cells, especially in view of the current tendency to move to high-temperature operation. The advantages given by these hydrophilic perfluorinated materials for use in membrane technology are discussed. The properties and performance of Hyflon Ion membranes are compared with other perfluorinated membranes present on the market.

Self-emulsifying polymerization (SEP) of 3,6-dioxa-Δ 7-4-trifluoromethyl perfluorooctyl trifluoromethyl sulfonimide with tetrafluoroethylene

The copolymerization of an insoluble gaseous monomer with a soluble monomer that behaves as its own surfactant is described. This process is called self-emulsifying polymerization (SEP). A variety of sulfonamide monomers can be used in SEP, but current work has focused on copolymers of tetrafluoroethylene with 3,6-dioxa-Δ 7-4-trifluoromethyl perfluorooctyl trifluoromethyl sulfonimide 1. 19F NMR was used to determine the critical micelle concentration of the sodium salt of the monomer 1 for the SEP with tetrafluoroethylene.