Hexafluoropropylene Research Articles

Dissolving Perfluoropolymers in Supercritical Carbon Dioxide

A copolymer of TFE (tetrafluoroethylene) and HFP (hexafluoropropylene) was dissolved in supercritical (SC) CO 2 at about 200 °C and 100 MPa. The copolymer contained 19.3 mol % HFP and had an ultimate melting point of 200 °C. Theoretical predictions for phase diagrams of CO 2 with TFE homo-and copolymers indicate solubility at ≥100 MPa for all systems. The temperature requirements for solubility are about 300 °C and greater for PTFE [poly(tetrafluoroethylene)], with lower temperatures required for the copolymers. The experimental results for the low-melting HFP copolymers are reasonably consistent with these phase diagrams, leading us to believe that PTFE should be soluble near the predicted conditions.

Study on the synthesis of perfluorovinyl‐sulfonic functional monomer and its copolymerization with tetrafluoroethylene

AbstractTetrafiuoroethylene (TFE) and hexafluoropropylene (HFP) were subjected to reactions with freshly distilled sulfur trioxide to obtain 1‐fluorosulfonyldifluoro‐acetylfluoride (FSDFAF, yield 65–70%) and pentafluoro‐2‐propenylfluorosulfate (PPFS, yield up to 50%). A subsequent reaction of FSDFAF with PPFS under anhydrous conditions led to a preparation of 2‐(1‐pentafluoro‐2‐propenyloxy)tetrafluoroethanesulfonyl fluoride (PPOTESF, yield 40–41%) whose structure was proved by both infrared (IR) spectroscopy and nuclear magnetic resonance (19F NMR). TFE was copolymerized with PPOTESF in bulk by using a free radical initiator of the hydrocarbon type at a temperature of 50°C. Various TFE/PPOTESF mole ratios were employed and the presence of sulfonyl fluoride (SO2F) functional groups in the copolymers was proven by IR spectroscopy. The copolymers were subjected to alkaline hydrolysis and the SO2F content was found not to exceed 0.70–0.80 mEq/g with polymer yields in the range of 11–31%. The reactivity ratios r1 and r2 related to TFE and PPOTESF, respectively, were determined by using the Fineman‐Ross method. A random distribution of PPOTESF units along the polymeric chain, consisting mainly of TFE fragments, was found to exist. The copolymers had melting temperatures 40–45°C lower than polytetrafluoroethylene and were thermally stable to 305–315°C. © 1993 John Wiley & Sons, Inc.

Thermal degradation of commercial fluoropolymers in air

Weight-loss data have been obtained for the degradation in air of tetrafluoro-ethylene (TFE) homopolymer, its copolymers with hexafluoropropylene (HFP) and perfluoropropylvinyl ether (PPVE), and for TFE/ethylene/perfluorobutylethylene terpolymer. The nature and approximate amounts of the gaseous degradation products were also determined. The temperature range studied (from 150 to 525°C) includes the range of recommended continuous use and processing temperatures for these commercial resins. None of the six polymers studied showed any detectable weight loss (<0·05%/h) at their continuous use temperature; but three had weight losses at their maximum processing temperatures that were greater than 1%/h. Several of the degradation gases found are quite toxic, emphasizing the need for good local exhaust ventilation during processing.

Preparations of carboxylic acid esters containing heptafluoroisopropyl groups

The reaction of fluoroglyoxylic acid esters and fluoroformic acid esters with perfluoropropene (PFP) yielded perfluoro(3-methyl-2-oxobutyric) acid esters and perfluoroisobutyric acid esters, respectively. Oxamide derivatives and 2,3-quinoxalinediol have been prepared by the reaction of perfluoro(3-methyl-2-oxobutyric) acid esters with amines and o- phenylenediamine, respectively. Perfluoro(3-methyl-2-oxobutyric) acid esters give perfluoroisobutyric acid esters on heating in the presence of fluoride ion in an aprotic solvent.

Deactivation of a Pt/Al 2O 3 catalyst during the oxidation of hexafluoropropylene

A 5% Pt/Al 2O 3 catalyst was exposed to hexafluoropropylene (HFP) at concentrations between 500 and 4,500 ppm in humid air at temperatures between 300 and 400°C. The catalyst was found to deactivate over all conditions investigated. Analysis of the catalyst following reaction exposure indicated that the catalyst support had been transformed to aluminum fluoride, and that virtually all of the support's surface area had been lost. The observed deactivation was attributed to degradation of the catalyst support, caused by a reaction between the alumina support and product hydrofluoric acid. Under some conditions, the rate of catalytic deactivation was found to be proportional to the number of moles of hexafluoropropylene reacted.

Ion‐exchange copolymers based on tetrafluoroethylene, hexafluoropropylene, and acrylic acid

AbstractPeroxide‐induced copolymerization of tetrafluoroethylene (TFE) with hexafluoropropylene (HFP) and acrylic acid (AA) at different molar ratios of monomers, reaction time, pressure, and initiator concentration was studied. By means of IR spectroscopy and temperature and phase characteristics of the copolymers obtained it was proved that a ternary copolymer of TFE, HFP, and AA was synthesized. Fluoro‐containing polymers with ion‐exchange capacities up to 0.8 meq/g were obtained. The composition of binary TFE‐HFP and ternary TFE‐HFP‐AA copolymers and some of their characteristics were determined. Copolymerization takes place mainly in the stationary state with an induction period. Polymerization rate R ∼ [In]0.7, which is presumably connected with chain transfer reaction to AA.

Reactions of hexafluoropropene trimers with thiols

Reactions of the hexafluoropropene (HFP) trimers — perfluoro-3-isopropyl- 4-methyl-2-pentene (I) and perfluoro-3-isopropyl-2-methyl-2-pentene (II) with thiols have been studied. Trimer (I) was shown to give vinyl derivatives by substitution of fluorine atoms. Interaction of trimer (II) with thiols produces alkyl(aryl)perfluoroalkadienylsulfides. A mechanism for their formation, including nucleophilic attack of the thiolate-anion at a RS-group of intermediate alkyl(aryl)perfluoroalkenylsulfides is proposed. The first perfluoroalkylsubstituted thiete is obtained.

Toxicology of Fluorine-Containing Monomers

Fluorine-containing monomers form the basis for production of a large number of commercially important polymers. Most of the polymerization occurs as gas-phase reactions, hence the hazards associated with the monomers arises primarily from inhalation. The chemicals covered in this review include bromotrifluoroethylene (BTFE), chlorotrifluoroethylene (CTFE), hexafluoroacetone (HFA), hexafluoroisobutylene (HFIB), hexafluoropropylene (HFP), perfluorobutylene (PFBE), tetrafluoroethylene (TFE), trichloropropene (TFP), vinyl fluoride (VF), and vinylidene fluoride (VF2). The amount of toxicologic information available on the compounds is relatively small and for certain of these the information consists is short-term or acute, hence the current need to make predictions of biologic activity based on analogy or chemical reactivity is great. In animal models and in man, these monomers may be absorbed into the body at varying rates and the metabolism ranges from extensive to little in a species, dose, and chemical specific fashion. The major toxicologic target of these materials is the kidney, and the degree of involvement depends greatly on the excretion patterns and metabolic profiles of the monomers. However, other target sites exist, such as the reproductive system for HFA, making the use of structure-activity relationships difficult.

Fluoroelastomers-dependence of relaxation phenomena on composition

The dynamic-mechanical properties of some fluoroelastomers were determined as a function of composition at low frequency (≈ 1 Hz), by means of a free oscillation torsion pendulum, between −180°C and the softening point. Vinylidenefluoride (VDF)-hexafluoropropene (HFP) copolymers of molar composition 0–39% HFP and terpolymers of VDF and HFP with up to 30mol% tetrafluoroethylene (TFE) and a constant VDF to HFP molar ratio of 3.4 were considered. Two relaxation processes typical of the amorphous phase were found. The first, located at about −87°C, is related to local motions and the transition temperature was found to be independent of composition for copolymers, while it depends on TFE molar content for terpolymers. The second is related to the glass transition and the transition temperature depends on the composition. However, for semicrystalline copolymers the double glass transition phenomenon was observed. When crystallinity goes to zero at about 20 mol% HFP, only one transition is observed. It was also found that ordered structures can take place for terpolymers when TFE molar concentration exceeds 20%. The crystal disorder transition of pure PVDF (75°C) is observed also for low HFP concentrations but the transition temperature is strongly reduced. Analogies between the VDF-HFP and E-P systems are also discussed.

Some thermodynamic properties of tetrafluoroethene‐hexafluoropropene copolymers

AbstractCopolymers of tetrafluoroethene (TFE) with hexafluoropropene (HFP) have been prepared in the 0‐14mol% HFP composition range. Their melting temperatures (Tm), enthalpies (ΔHf) and entropies (ΔSf) of first and second fusion, and crystallinities (X) according to x‐ray diffraction(x.r.d.) and differential scanning calorimetry (d.s.c.) have been determined. The results indicate that ΔHf/Xx.r.d of the polymer crystals decreases with higher HFP content.

Effects of strain‐induced crystallization on the elastic and thermoelastic properties of some fluoroelastomers

AbstractA Viton copolymer containing vinylidene fluoride (VF2) and hexafluoropropylene (HFP), and a terpolymer containing VF2, HFP, and tetrafluoroethylene (TFE) were cross linked using varying amounts of Bisphenol AF to yield two series of fluoroelastomer networks, Stress‐strain isotherms in elongation were determined for these samples at several temperatures and at two degrees of swelling with phenyl acetate. Strain‐induced crystallization was observed, as evidenced by upturns in the isotherms at high elongations. It appears to be more pronounced in the terpolymer samples, presumably because the TFE units not only can crystallize themselves, but can co‐crystallize with the VF2 units. The crystallization was found to persist upon moderate increase in temperature, but was suppressed when the networks were swollen, Thermoelastic (force‐temperature) measurements were used to obtain values of the fraction fe/f of the elastic force that is due to energetic effects. Negative values were obtained for both types of samples and, in the case of two samples studied in detail, their magnitudes increased with increase in elongation. The magnitudes were larger and the increases more pronounced in the case of the terpolymer networks, as would be expected from a greater tendency for straininduced crystallization.

Formation of stable radicals in the radiolysis of hexafluoropropylene

The radiolysis of the dimer (perfluoro-4-methyl-2-pentene) and trimer (perfluoro-2,4-dimethyl-3-ethyl-2-pentene) of hexafluoropropylene (HFP) gives thermally stable perfluoroalkyl radicals. The stability of these radicals is apparently related to the steric isolation of the unpaired electron. The formation of a growing oligomer chain perfluoroalkyl radical which is stable in the liquid phase is observed upon the radiolysis of hexafluoropropylene. The radio-chemical yield of such a radical G approx. 0.05 x 10/sup -2/ eV. The low capacity of hexafluoropropylene to undergo homopolymerization is related to the formation of similar inactive radicals.

Reactions of vinilydene fluoride-hexafluoropropene copolymers

The alkaline dehydrofluorination of Vinylidene Fluoride (VDF) -Hexafluoropropene (HFP) copolymers in dimethylacetamide has been reported by Schmiegel [1]. Basing on the reduction of 19F NMR signals related to HFP-VDF-HFP sequences and the apprearance of small low-field resonances attributed to allilic CF 3, he suggested that the reaction takes place at HFP-VDF-HFP sequences, to give conjugated dienes and α, β unsaturated ketones deriving from OH − addition to dienes. This communication presents a study of the dehydrofluorination of VDF-HFP copolymers in THF, by alcoholic KOH. The reaction has been followed by analysis of the fluoride ion in solution. The intrisinc viscosity of the polymer did not change after elimination of up to 7.9 x 10 −4 moles F − per g polymer. Higher reaction extents resulted in a decrease of intrinsic viscosity, suggesting polymer chain degradation. The reation products exhibit IR absorptions at 1720, 1684 and 1638 cm −1, that can be attributed to isolated double bonds and/or carbonil groups. No IR bands indicate conjugation that is also not evidenced by UV spectra. 19F NMR spectra are similar to those reported by Schmiegel, but show a larger variety of new CF 3 signals, both in the low-field and the usual CF 3 regions. The Tg of the unsaturated polymers and the reation of these products with phenate anions have also been studied.

Homo- and copolymers of vinylfluoride

In this paper some special features of emulsion polymerization of vinylfluoride (VF) and its copolymerization with vinyliden fluoride (VDF), threefluoroethylene (ThFE), tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) in the presence of different emulsifiers, initiated by ‘redox’-systems, have been studied. It was shown that emulsifiers by their activity in the reactions of homo- and copolymerization of VF are placed in the following sequence: anionic- > nonionic- > cation-active compounds. The highest rate of homo- and copolymerization is observed while using perfluorocarbonic acids and their salts. It was established that the chemical process proceeds through the three stages: induction period, postnuclear stationary stage and finishing stage, typical for the emulsion (co)polymerization of polar monomers being low soluble in water. In all cases the obtained copolymers were enriched in VF compared to the initial monomer mixture. High activity of VF as well as low stability of radical, obtained from the VF molecule, lead to the fact that during copolymerization with fluorolefines it is charecterized by high values of copolymerization constants (r VF ⩾ 1). Introduction of fluorolefine links leads to the increase of heat-, thermo- and chemical stabilities and simplification of polyvinylfluoride conversion. A possibility of conversion of homo- and copolymers of VF into films, fibers and coverings is shown.

Fluoro-olefin chemistry Part 20 [1]. Reaction of hexafluoropropene with alcohols

Reaction of hexafluoropropene (HFP) with a series of alcohols under thermal, photochemical or peroxide-initiated conditions affords the 1:1 adducts CF 3CHFCF 2CR 1R 2OH (R 1 = H, R 2 = H, Me, Pr n or CF 3; R 1 = Me, R 2 = Me or Et) in high yield via a radical chain mechanism. Adduct are not formed with the alcohols (CF 3) 2CHOH and CF 3CHFCF 2CH 2OH. Other 1:1 adducts of structure CHF 2CF(CF 3)CH 2OH and CH 3(C 2H 3CF 2CHFCF 3)CH 2OH are formed as minor products in the methanol and n -butanol reactions, respectively.

Particle formation in the soapless emulsion copolymerization of vinylidene fluoride and hexafluoropropene

The comonomer system based on vinylidene fluoride (VDF) and hexafluoropropene (HFP) has been polymerized in soapless emulsion, at various pressures of the gaseous feed and different concentrations of the free-radical initiator. The particle size and number, evaluated as a function of conversion, suggest a rather long nucleation period. In Smith-Ewart's Interval II the limiting particle number decreases with increasing monomer fugacity (which is proportional to the monomer concentration in water), and increases with increasing initiator concentration. The kinetic data cannot be fully accounted for by changes of particle number. On the contrary, there is evidence that the average number of free radicals per particle is affected by experimental conditions and follows a trend very similar to that predicted by Stockmayer's model.

Structure/activity studies of the nephrotoxic and mutagenic action of cysteine conjugates of chlgro and fluoroalkenes

The cysteine conjugates of the nephrotoxins hexachlorobutadiene (HCBD), tetrafluoroethylene (TFE) and hexafluoropropene (HFP), together with those of trichloroethylene and perchloroethylene, have been chemically synthesized and a relationship determined between their structures and their nephrotoxicity and mutagenicity in vitro. All of the conjugates had a marked effect on the uptake of both the organic anion p-aminohippuric acid (PAH) and the cation tetraethylammonium bromide (TEA) into rat kidney slices, suggesting activation of the conjugates in the slices to a toxic species which interferes with ion transport. This observation is consistent with the known nephrotoxicity of HCBD, TFE and HFP in vivo. Each of the conjugates was found to be metabolised by rat kidney slices and by semi-purified rat kidney beta-lyase to pyruvate, ammonia and an unidentified reactive metabolite. When semi-purified beta-lyase was used stoichiometric amounts of pyruvate and ammonia were produced. Although all of the conjugates were activated by beta-lyase and had a similar effect on ion transport their mutagenicity differed markedly. The conjugates of HCBD, trichloroethylene and perchloroethylene were mutagenic in the Ames bacterial mutation assay when activated by rat kidney S9. Metabolic cofactors were not required suggesting that activation was due to the enzyme beta-lyase. In the same assay the conjugates of TFE and HFP were not mutagenic either in the presence or absence of rat kidney S9 and cofactors. With a limited number of cysteine conjugates a clear distinction has been identified between the conjugates of chloroalkenes which were were similarly nephrotoxic but were not mutagenic. The mutagenicity of the cysteine conjugate of HCBD is consistent with the known renal carcinogenicity of this chemical.

Synthesis and properties of some hexafluoropropene-1,1-difluoroethene copolymers

Hexafluoropropene (HFP) — 1,1-difluoroethene (VDF) copolymers have been synthesized in the 0–16 mole % HFP range and the results of a physico-chemical characterization by means of XRD (cristallinity index) and DSC techniques are related to the microstructure of the polymers, as determined by 19F NMR. The addition of a small percentage of the HFP comonomer does not affect the polymorphism of poly(vinyl-idenefluoride).

Effects of inhaled chlorotrifluoroethylene and hexafluoropropene on the rat kidney

Male Fischer-344 rats were subjected to 4.0 hr inhalation exposure to chlorotrifluoroethylene (CTFE) concentrations ranging from 100 to 540 ppm, or hexafluoropropene (HFP) concentrations ranging from 380 to 1200 ppm. Within 2 days following exposure, the rats exhibited dose-related proximal tubular necrosis, diuresis, increases in urinary fluoride, urinary lactic dehydrogenase (LDH) activity, serum creatinine, and BUN. The toxicities of CTFE and HFP were similar except that (1) CTFE was the more potent renal toxin and (2) HFP produced necrosis of the pars recta and pars convoluta portions of the proximal tubule, while CTFE produced necrosis of only the pars recta. At the lowest exposure concentrations, diuresis was the most sensitive index of toxicity manifesting 50% increases in water intake and 25% decreases in urine osmolality. Increases in urinary LDH activity correlated with the degree of proximal renal tubular necrosis, with greater than 100-fold increases at the highest concentrations of CTFE and HFP. At 100 ppm, CTFE induced renal dysfunction (mild diuresis), but no significant increase in urinary LDH nor necrosis were apparent. All concentrations of HFP studied produced necrosis within 24 hr postexposure, with tubular cell regeneration apparent within 4 days.

Reactions of amines with a dimer of hexafluoropropene and with a perfluorovinyl sulfide prepared with hexafluoropropene

Some reactions of amines with a perfluorovinylsulfide, (CF 3) 2CFSC(CF 3)CFCF(CF 3) 2, prepared from hexafluoropropene (HFP) and sulfur [1] are compared to reactions of the same amines with the thermodynamic dimer of HFP, (CF 3) 2CCFCF 2CF 3. Many new ketenimines, eneamines, amidines, nitriles, and quinoline derivatives are reported.