Heat capacity of fluoropolymers

The heat capacities of poly(vinyl fluoride), poly(vinylidene fluoride), and polytrifluoroethylene have been measured between 80 and 340°K. The results can be expressed as the sum of two terms: the optical contribution calculated from the vibrational band assignments in the literature and the acoustical contribution calculated according to the Tarasov continuum model. Combining our data with those for polyethylene and polytetrafluoroethylene, it is concluded that the force constant for one-dimensional intrachain interaction is approximately constant for all polymers with carbon backbones. The force constant for three-dimensional interchain interaction is one order of magnitude smaller than the one-dimensional force constant, and decreases when the hydrogen atoms in polyethylene are replaced by fluorine atoms. The thermodynamic functions for the three polymers have been evaluated. Glass transitions at 228°K and 305°K have been found in poly(vinylidene fluoride) and polytrifluoroethylene, respectively.     

Mechanisms of pyrolysis of fluoropolymers

A systematic study of the mechanisms of the pyrolysis of fluoropolymers was made by means of pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and direct Py-MS. For perfluoropolymers and chlorine-containing fluoropolymers the depolymerization reaction predominates during pyrolysis. However, the introduction of OCF₃ groups into perfluoropolymers in place of F atoms brings about significant changes in their mode of degradation. The OCF₃ groups activate the F atoms attached to the same carbon atoms and make them easier to transfer. Therefore, random chain cleavage accompanied by the F transfer becomes predominant in the course of the pyrolysis. When the F atoms of perfluoropolymers are partly replaced by H atoms, elimination of hydrogen fluoride and chain cleavage accompanied by H transfer would occur with great ease. For fluoropolymers containing H, Cl and OCF₃ as side groups, the depolymerization, the elimination of hydrogen chloride and hydrogen fluoride and the random chain cleavage accompanied by H and F transfer would occur simultaneously and compete with each other.     

High-temperature aging of Halar film. II. Analysis of melting behavior

Melting behavior of an experimental Halar film, a predominantly alternating 1:1 copolymer of ethylene (E) and chlorotrifluoroethylene (CTFE), has been studied. Differential scanning calorimetry (DSC) reveals single or double melting peaks, depending upon the thermal history. The lower-temperature melting peak T_m1 is produced only by the thermal treatment and shows a strong dependence on annealing time and temperature. On the basis of the DSC and x-ray data it can be suggested that T_m1 represents the melting of relatively small crystallites formed upon annealing. The higher-temperature melting peak T_m2 is always shown at 238°C. (Note: the specification for commercial Halar product is 240°C. The slightly lower melting temperature reported in this study is probably due to the fact that we are dealing with an experimental melt-processed material.) On the basis of the heating rate study we propose that Halar crystallizes with stable crystals (T_m2 = 238°C) regardless of the crystallization conditions, i.e., quenching, slow cooling, or even annealing. Crystals of Halar have a heat of fusion of approximately 35 cal/g or 146 kJ/kg. Detailed analysis of the melting behavior of Halar is presented.     

A challenge to novel fluoropolymers

Perfluoro(vinyl ether) derivatives are extremely versatile monomers in preparing a variety of functional fluoropolymers. In this paper, two challenging topics in the development of novel fluoropolymers will be introduced. Carboxylated perfluoro(vinyl ether) can be copolymerized with tetrafluoroethylene to afford perfluorinated ion-exchange membranes, which realize the innovative process for pollution-free and energy-saving chlor-alkali production. Another topic includes the discovery of selective cyclo-polymerization of specially designed difunctional perfluoromonomers such as perfluoro(allyl vinyl ether) which is readily derived from the carboxylated perfluoro(vinyl ether). The novel perfluoropolymer with a cyclic structure in the main chain is characterized by an exceptional transparency, and has been commercialized with expectation of major applications in electronics industries.     

Structure-property relationships for carbochain fluoropolymers

Polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF) and polychlorotrifluoroethylene (PCTFE) were studied by differential calorimetry at normal pressure in the temperature interval 130–555 K, and by pressure dilatometry in the temperature interval 303–545 K and in the pressure range 14–70 MPa. Pressure derivatives of the melting temperature,dT _m/dP, were used to calculate the true melting entropy S _m from the Clausius-Clapeyron equation, while equilibrium values of the melt specific volume were treated according to the Simha-Somcynsky cell theory. Comparison of the experimental data for PVF, PVDF and PCTFE with pertinent published data for polyethylene (PE) and polytetrafluoroethylene (PTFE) showed that a steady decrease of S _m and of the conformational contribution to S _m reflects the increase of the equilibrium chain stiffness as the hydrogen atoms of the hydrocarbon chain (PE) are substituted with bulkier fluorine and/or chlorine atoms (PCTFE, PTFE), while a concomitant drop of the pressure reducing parameter from the cell model and an increase of melt compressibility and the derivative,dT _m/dP, should be attributed to the increase of the free volume fraction of the melt in the series, PE to PTFE.     

Effect of gamma radiation on fluoropolymers

A series of fluoropolymer films were synthesized by reacting several bisphenol monomers with 1,3‐bis(1,1,1,3,3,3‐hexafluoro‐2‐pentafluorophenyl methoxy‐2‐propyl)benzene via a nucleophilic aromatic substitution to form polyethers. The bisphenols used included two diphenol‐substituted spirodilactams (SDL; aliphatic and aromatic), biphenol, bisphenol A, bisphenol AF, bisphenol O, and bisphenol F to form seven different polymers. Polymers were irradiated by a Gamma beam 651‐PT at a dose rate of 10.5 kGy/h; the absorbed dose in each film was varied between 300 and 1000 kGy. The effect on the chemical structure upon radiation was studied by DSC, TGA, FTIR‐ATR, and NMR after and before irradiation. Thermal analysis showed a lessened thermal stability and a lower T_g after irradiation. Further, irradiation caused a decrease in molecular weight as a result of cleavage of sp³ bonds. These data allowed calculation of the radiochemical yield scission (G_s) for each of these polymers. The SDL aromatic system proved the most radiation‐resistant. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1617–1626, 2009     

Quantum chemistry studies of unbranched fluoropolymers

The results of quantum chemistry calculations of energy and topology parameters, vibration and NMR spectra of model fluorocarbon and unbranched hydrocarbon molecules are presented in this work. The formation of radicals and branches in fluorocarbon molecules and mechanisms of hydrogen substitution by fluorine at fluorination of hydrocarbon paraffins and polymers are discussed based on obtained results.     

Bibliometric analysis of scientific publications on fluoropolymers

Scientific publications on fluoropolymers are sought in the Chemical Abstracts Plus database accessed via the SciFinder system. For the period 1946–2010, nearly 116 000 publications containing the search term fluoropolymers as the main concept are found. For nearly 75 000 publications over the period 2000–2009, a detailed bibliometric analysis is performed on the basis of thematic sections and subject headings of the database, substances, publication types, languages and authors of publications, journal titles, and organization names. On the basis of the results, recommendations for improving Russian indicators in the field of fluoropolymers are suggested.     

Blends and composites based on fluoropolymers

Fluoropolymers represent a rather unique group of polymeric materials. Essentially, current most widely used commercial fluoropolymers are derivatives of ethylene and propylene, also known as fluorocarbon polymers. Other, more complex fluorinated polymers are also important technically, but these are used in considerably smaller amounts. Because of the unique chemistry and properties, fluorocarbon polymers rarely form good blends. The only exceptions are homopolymers and copolymers of vinylidene fluoride, which form blends based on thermodynamic compatibility with certain polymers, such as acrylates and methacrylates. However, most known fluoropolymers can be used to produce fiber and fabric reinforced composites as well as composite films and coatings.     

Electron beam irradiation of fluoropolymers containing polyethers

A highly fluorinated monomer, 1,3-bis(1,1,1,3,3,3-hexafluoro-2-pentafluorophenyl methoxy-2-propyl)benzene (12F-FBE) was polymerized with some diphenols by polycondensation and then was electron beam irradiated between 100 and 1000 kGy to determine degradation radiochemistry yield (G_s) by gel permeation chromatography (GPC). The samples were characterized after irradiation by DSC, FTIR, and nuclear magnetic resonance (NMR). The fluoropolymers show apparent degradation in mechanical properties at 300 kGy, except 12F-FBE polymerized with biphenol and bisphenol A, when they did not show any apparent physical change up to 300 kGy; and continue to be flexible and transparent, with a radiochemical yield scission (G_s) of 0.75, 0.53, 0.88, and 0.38 for 12F-FBE/SDL aliphatic, 12F-FBE/biphenol, 12F-FBE/bisphenol A, and 12F-FBE/bisphenol O, respectively. The number average molecular weights for three of the polymers decrease upon 1000 kGy irradiation to 10% of their original values; however, the polymer from bisphenol A is much more stable and its M_n decreases to only 24% of original.     

The use of fluoropolymers to protect semiconductor materials

Fluoropolymers are the materials of choice for many materials integrity management applications within the microelectronics industry. This brief overview discusses common types of fluoropolymers and the stringent requirements of semiconductor-processing environments. Fluoropolymers are used in a wide variety of such fluid and device handling applications because they provide a unique combination of toughness, purity, and chemical resistance.     

Radiooxidation of fluoropolymers: Identification of oxidation products

Radiation effects on fluoropolymers induced by high‐energy irradiation were investigated. Poly(fluorovinylidene‐co‐hexafluoropropylene) [P(VDF‐HFP)] films were irradiated with γ rays in air. Peroxy radicals formed by irradiation in the presence of oxygen were partially converted into more stable products such as hydroperoxides, alcohols, and acids. These oxidation products were identified by Fourier transform infrared spectroscopy. Specific chemical treatments were carried out to identify and separate overlapping absorption bands. Model compounds were also used. On the basis of the results, a mechanism of degradation for γ‐irradiated P(VDF‐HFP) is proposed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1509–1517, 2003     

Utilization of oxygen difluoride for syntheses of fluoropolymers

The utilization of OF₂, for chain extension of polyperfluoropolyenes, insertion of functional groups into the polymer structure and addition copolymerization with perfluorodiene is described. The results of reactions of OF₂ and polyperfluoro-1,2- and -1,4-butadiene indicate that conditions can be selected either to extend the polymer chain or to insert acyl fluoride groups into the polymer structure. Ambient and higher temperatures favor insertion of acyl fluoride groups. At 0°C chain extension occurs without introduction of acyl fluoride groups. Preliminary results on the novel synthesis of perfluoroalkylene oxide polymer by addition copolymerization of perfluorobutadiene and OF₂ is also reported.     

New findings on thermal degradation properties of fluoropolymers

In this paper, the thermal degradation properties of Viton A and Fluorel are investigated by both isoconversional and combined kinetic analysis methods using non-isothermal thermogravimetry technique. It has been found that the heating rate has little affect on the degradation residue of Fluorel and Viton A, where around 1.3% char was formed for Fluorel and 3.5% for Viton A. Different from the literature, the decomposition of Viton A should be considered as an overlapped dehydrofluorination and carbon chain scission process, with activation energy of 214 ± 11 and 268 ± 13 kJ mol^?1, respectively. The effect of dehydrofluorination on degradation of Fluorel is not so significant due to low content of H, and hence, it could be considered as a single-step mechanism with average activation energy of 264 ± 14 kJ mol^?1. The thermal stability of Fluorel is much better than that of Viton A, and the predicted half-life is around 218 min for Fluorel and 49 min for Viton A at 420 °C, which are consistent with experimental values. If using a single-step model as in the literature for Viton A, its half-life at 420 °C would be underestimated for >20%.     

New pentafluorothio(SF5)fluoropolymers

New fluorinated polymers containing the pentafluorothio group have been prepared from SF₅Br and the appropriate fluoroolefin under reaction temperatures of 90±5°C and autogeneous pressures of up to 90 atmosphere for periods of four days to two weeks. With ethylene, FCH₂CH₂Br and SF₅CH₂CH₂Br were formed. A new monomer addition product, SF₅CF₂CF₂Br, is also reported for the first time.     

Amorphous fluoropolymers - a new generation of products

Poly(tetrafluoroethylene) (PTFE) already known since 50 years, Is a unique material among plastics due to its chemical inertness, heat resistance, electrical insulation properties and low coefficient of friction. Its high melt viscosity needs special ways of processing. That fact led to the development of melt-processible fluoropolymers such as Perfluoroethylene-propylene (FEP) and Perfluoroalkoxy (PFA). Now we have a third generation which is an amorphous fluorpolymer made by copolymerizing tetrafluoroethylene with 2,2-bis (trifluoromethyl) - 4,5 - difluoro -1,3 - dioxole. The bulky cyclic structure prevents the normal crystallisation as with PTFE polymers. The amorphous fluoropolymers have high clarity and dissolve in selected solvents. Having C-F, C-C and C-O bonds the well known properties as high temperature and chemical resistance are retained. Dielectric constant is in the range 1.83 - 1.93 up to 10.00 MHz the lowest of any plastic material. Optical properties are also very special. Refractive index is very low, in the range 1.29 - 1.32. Transmission is high from UV to IR and the polymer is not photo-degraded. The unique electrical and optical properties, coupled with high chemical and thermal stability, plus the ability to work from solution offers a powerful tool for those working on the frontiers of technology.     

Use of telechelic fluorinated diiodides to obtain well-defined fluoropolymers

Different methods of synthesis involved in the preparation of fluorinated telechelics (or ,ω-difunctional compounds) from ,ω-diiodoperfluoroalkanes for obtaining well-defined fluoropolymers are described. This review focuses on molecules in which fluorinated chains are located on the backbone and not in a lateral position. First, a bibliographical approach develops the syntheses of ,ω-diiodoperfluoroalkanes (1) either by chemical transformations of telechelic derivatives or by telomerisation of fluoroolefins with molecular iodine or diiodoperfluoroalkanes. Then, fluorotelechelics are synthesised by means of four different processes: (a) by the chemical change in the presence of metalic salts; (b) from the bismonoaddition of 1 to ω-functional unsaturated derivatives; (c) from the bis(monoethylenation) of 1 followed by difunctionalisation (e.g., nucleophilic substitution); (d) from the coupling reactions between 1 and -iodo-ω-functional reactants. Finally, this review describes how several well-defined fluoropolymers can be produced from these fluorinated telechelics. Their specific chemical, physical and thermal properties are discussed with regard to modern industrial requirements.     

Modification of fluoropolymers by means of electron beam irradiation

High molecular weight polytetrafluoroethylene (PTFE) is transformed to free-flowing micropowder by treatment with electron beams. In case of irradiation in presence of air carboxylic acid fluoride groups are incorporated which rapidly hydrolyze to carboxylic groups in the surface-near regions due to atmospheric humidity. These polar groups reduce the hydrophobic and oleophobic properties so much that homogeneous compounding with other materials becomes possible. In addition to PTFE, copolymers of tetrafluoroethylene with hexafluoropropylene (FEP) and perfluoropropylvinylether (PFA) were modified. In case of identical irradiation conditions, the concentration of carboxylic groups is much higher in FEP and PFA than in PTFE, which is due to the lower crystallinity of the copolymers.

Electron beam irradiation of PTFE was performed in vacuum at elevated temperature above the melting point. The changes in the chemical structure were studied. The concentration of CF₃ branches was found to be much higher as compared to room temperature irradiation.

In a practical test PTFE micropowders functionalized by electron irradiation were compounded with epoxy resins, with polyoximethylene and with polyamides. Such compounds are characterized by very good frictional and wearing behaviour in dry-running tests.     

Composite materials based on fluoropolymers and oxyfluoride glasses

It was shown that molded specimens of polymer composite materials can be obtained by an extrusion method by melt blending of Fluoroplast F-2 MB (modified poly(vinylidene difluoride)) and oxyfluoride glasses of the composition 3B₂O₃ (40SnF₂–30SnO–30P₂O₅). The compositions of the observed phases of the composites were determined. Conclusions were made on the incompatibility of the components, their dispersion distribution, and strong adhesion interaction. Data on the nano level of the blending of the components were obtained. The elongation and Brinell hardness were measured in the composites with various (0–50 vol %) oxyfluoride contents. It was concluded that it is possible to produce composites based on fluorinated hydrocarbon and fluoroxide polymers.     

Drop size dependence of contact angles on two fluoropolymers

Young’s equation predicts that the contact angle of a liquid drop is independent of its size. Nevertheless, large drop size dependences of contact angles have been observed, especially for millimetre-sized drops, on a variety of solid surfaces. We report new measurements of drop size dependence of contact angles for several liquids on two fluoropolymer surfaces, Teflon AF 1600 and EGC-1700. We demonstrate a new strategy for contact angle measurement that allows detection of approximately 0.1° changes in the contact angle during the growth of a drop. We find that on the surfaces examined, drop size dependence of contact angles is ten times smaller than on all previously studied fluoropolymers at the millimetre scale. The data are insensitive to various attempted surface modifications. We discuss the interpretation of the data and possible physical sources.