Mechanism of the initiation of low-temperature radiation telomerization of tetrafluoroethylene in hexafluoroisopropanol

ESR and IR spectroscopy and scanning calorimetry are used to investigate the mechanism of low-temperature radiation telomerization of tetrafluoroethylene (TFE) in hexafluoroisopropanol (HFIP). It is found that the low-temperature telomerization of TFE in HFIP proceeds via an ion-radical mechanism. This process is initiated by the radical anions (CF₃)₂C^·-O^? formed during the deprotonation of OH groups of primary hydroxyl radicals (CF₃)₂C^·-OH exhibiting strong acidic properties. An interpretation of ESR spectra of irradiated HFIP recorded at 230–240 K is proposed with regard to the anisotropy on β-fluorine atoms and estimates of the angles between the corresponding C-F bonds and the axis of the unpaired electron orbital.     

Radiation telomerization of tetrafluoroethylene in tetrahydrofuran

According to DSC, DTG, and GPC data, H(CF₂CF₂)nC₄H₇O telomers with a chain length of n = 1−4 and T _b ≈ 170−200°C were formed during the radiolysis of a binary mixture of tetrafluoroethylene + tetrahydrofuran in a molar ratio of (0.37–2)/1 between the reactants at room temperature. IR spectroscopy and quantum-chemical calculations demonstrated that telomerization occurred with chain transfer through the α-hydrogen of the furan ring.     

The specifics of radiation telomerization of tetrafluoroethylene in chlorinated solvents and telomer properties

Radiation telomerization of tetrafluoroethylene in butyl chloride, chloroform, and carbon tetrachloride has been investigated. The chain length of telomers and their solubility and thermal stability depend on the initial monomer concentration and telogen properties. In the case of telomerization in chloroform and carbon tetrachloride, the yield, the chain length, and the thermal stability of the telomers are significantly higher than those in butyl chloride, in which the process is less efficient but soluble telomers having a short chain length and exhibiting quite high thermal resistance are produced. The molecular structure of the telomers has been studied by IR spectroscopy.     

Radiation-initiated telomerization of tetrafluoroethylene in 1,2-dibromotetrafluoroethane

The kinetics of the radiation telomerization of tetrafluoroethylene in 1,2-dibromotetrafluoroethane has been studied. It has been shown that the process occurs very efficiently in the perfluorinated solvent; small doses of γ-radiation (~2 kGy) are required for the complete conversion of the monomer. Telomers with a chain length of 120–360 tetrafluoroethylene units and high thermal stability are formed in the reaction. The structure and properties of the telomers have been studied by IR spectroscopy, thermogravimetry, and elemental analysis.     

Kinetics and mechanism of radiation telomerization of tetrafluoroethylene in hexafluoropropan-2-ol and trifluoroethanol

The kinetics of radiation telomerization of tetrafluoroethylene (TFE) in trifluoroethanol and hexafluoropropan-2-ol (HFIP) has been investigated by method of kinetic calorimetry. The nature of active centers initiating the process of telomerization of tetrafluoroethylene in hexafluoroisopropanol in the temperature range of 77—300 K was investigated by ESR spectroscopy. The molecular structure and properties of the obtained telomeres were studied by IR spectroscopy and TGA.     

Radiation telomerization of tetrafluoroethylene in butyl chloride solution

The kinetics of the radiation-initiated polymerization of tetrafluoroethylene (TFE) in butyl chloride has been studied. The rate of the process, the properties and yield of telomers obtained depend on the initial concentration of TFE (2.6–22 wt %) in the solution and the dose of γ-irradiation. The analysis of the measured IR absorption spectra and a possible scheme of the process allow to suggest that the main product of the reaction is C₄H₈Cl(C₂F₄) _n−1CF₂CF₂H with the formation of small amounts of C₄H₉(C₂F₄) _n−1CF₂CF₂H and Cl(C₂F₄) _n−1CF₂CF₂H. The average number of links in the telomer (n) increases from 7.6 to 16.1 when the concentration of the monomer in the solution varies in the range of 7–22 wt %. The length of the chain of the soluble telomers (n) does not depend on the initial concentration of TFE and makes ∼7.     

Copper-induced telomerization of tetrafluoroethylene with fluoroalkyl iodides

In the presence of catalytic amounts of cooper, telomerization of tetrafluoroethylene with fluoroalkyl iodides can be carried out at 80-100°C. As compared with usual high-temperature (∼200 °C) telomerization process, the reaction time required is much shorter.     

Radiation-initiated telomerization of tetrafluoroethylene in acetone at a constant monomer concentration

Kinetics of radiation-initiated polymerization of tetrafluoroethylene in acetone was studied at various initial concentrations (pressures) of the monomer in the reactor, which remain constant in the course of synthesis. Concentrated solutions of tetrafluoroethylene telomers were obtained and their properties were examined.     

Molecular-mass-distribution of oligomers in the products of tetrafluoroethylene telomerization in various solvents

The possibility of using differential thermogravimetry (DTG) for determination of the molecularmass-distribution (MMD) of oligomers in polymerization products has been experimentally and theoretically substantiated. The technique is based on the assumptions that the increase in the boiling temperature of oligomers with the increasing chain length is described by the additivity rule and the shape of DTG curves obeys the equation of mass transfer in the stationary convective flow created by evaporation. The results have been confirmed by gel-permeation chromatography and ¹⁹F NMR data. It has been shown that the chain length of oligomers produced via tetrafluoroethylene (TFE) telomerization in carbon tetrachloride, chloroform, acetone, and ethyl acetate reaches about 20–25 C₂F₄ units at an initial TFE concentration of C ₀ ≈ 0.5 mol/l. The MMD includes a low-molecular-mass component (n ≤ 5) in an amount that decreases with increasing C ₀ and a high-molecular-mass component, whose maximum shifts toward higher values of n with an increase in C ₀. The bimodality of MMD is explained in terms of decrease in the propagation rate constant with the accumulation of long oligomers.     

Molecular mass distribution of oligomers in products of tetrafluoroethylene radical telomerization

The molecular mass distributions (MMD) of perfluorinated oligomers in products of tetra-fluoroethylene (TFE) radical polymerization in various solvents (telogens) were determined from an analysis of differential thermogravimetric curves and data of gel permeation chromatography and mass spectrometry. Radiolysis of the telogens generates radicals initiating polymer chain growth. The choice of the solvent and TFE concentration makes it possible to obtain oligomers with the controlled average chain length from 4 for 40 CF₂ fragments and specified terminal groups. The polymerization of TFE in THF and propylene oxide affords oligomers with cyclic terminal groups capable of further polymerization due to ring opening. The appearance of two MMD maxima (low-molecular-weight at n ₁ ～6–8 and high-molecular-weight at n ₂ > 10 shifting towards high n with an increase in the TFE concentration) is caused by the formation of colloidal solutions of oligomers.     

Differential thermogravimetric analysis of the products of radiation-chemical telomerization of tetrafluoroethylene in acetone

Differential thermogravimetric (DTG) curves of the products of radiation-chemical telomerization of tetrafluoroethylene solutions in acetone with concentrations (c) of 0.06 to 2.0 mol/l were measured in the temperature range 20–600°C. The pattern of the DTG curves was determined by evaporation of telomers at c < 0.2 mol/l and their thermal degradation at c > 0.2 mol/l. Acetone-soluble telomers with an average chain length of less than 5 units prevail at c < 0.1 mol/l, whereas telomers with a chain length up to 15 units, which form colloid particles, dominate at higher c values. It was shown by means of atomic-force microscopy that such colloid solutions form coatings composed of submicron-sized particles.     

Radiation telomerization of tetrafluoroethylene in chlorinated telogens at a constant reactor pressure

The kinetics of the radiation-initiated telomerization of tetrafluoroethylene (TFE) in the solutions of telogens (butyl chloride, chloroform, methylene chloride, and carbon tetrachloride) at a constant monomer pressure in the reactor was studied. In the course of the Γ-irradiation of the reaction mixture, TFE telomers containing repeatedly soluble and insoluble fractions were formed. In chloroform, methylene chloride, and carbon tetrachloride, the rapidly occurring process of the synthesis of insoluble telomer made the main contribution to the total yield of products. For the solutions of TFE in butyl chloride, the rates of formation of soluble and insoluble telomers were almost the same. The average chain length and the thermal stability of the resulting telomers were evaluated.     

Formation of colloid solutions and gels during the radiation-chemical telomerization of tetrafluoroethylene in acetone

The polymerization of tetrafluoroethylene (TFE) is initiated by the radicals generated by the radiolysis of acetone. The oligomer chain length n increases with an increase in the initial monomer concentration C. The transition from the true to the colloid solution at C ≈ 0.07 mol/l takes place at an average telomer chain length of $ \bar n $ \bar n ≈ 5. The transition of the colloid solution into gel is observed at C ≈ 0.30–0.35 mol/l. The acetone/TFE ratio in the centrifugation sediment decreases with an increase in the centrifugal acceleration and C. Its minimal value of ∼4 is attained at C > 2 mol/l when $ \bar n $ \bar n ≈ 12–15. The mean particle diameter in the phase separation region is 0.6–0.8 μm. A scaling model of radical polymerization is proposed to explain the molecular-mass distribution of telomers.     

Low-temperature radiation chemistry

An overview of studies on the radiation-initiated chemical reactions of polymerization, copolymerization, graft polymerization, telomerization, oxidation, cryoozonolysis, hydrobromination of olefins, and chlorination of paraffins occurring at low and ultralow temperatures has been presented. Particular attention has been paid to self-oscillating reactions.     

Use of ionizing radiation for the study of the stabilization of tetrafluoroethylene

TFE is highly unstable. It can easily go through an explosive disproportionation reaction under polymerization. The present work proposes the use of ionizing radiation for the study of monomer stability by inducing the polymerization and disproportionation reactions. Radiation was used to promote the initiation of TFE polymerization with and without inhibitors. Inhibitors and TFE were irradiated by γ-rays from ⁶⁰Co. Small explosions with polymerization were observed yielding oligomer and polymer plus byproducts. It was shown that the initiation was completely inhibited by the addition of 0.1% of -pinene, dipentene, terpinolene or its mixture 1:1:1. In conclusion, radiation is a safe, reliable and easily controllable method to study TFE stabilization.     

Three-component one-pot synthesis of 1,2,3,4-tetrahydroquinoline derivatives in hexafluoroisopropanol

The one-pot aza-Diels-Alder reaction of substituted aromatic amines, ethyl glyoxylate and benzyl vinylcarbamate or N- benzyloxycarbonyl 2-pyrroline was conducted in hexafluoroisopropanol, providing the desired 1,2,3,4-tetrahydroquinline derivatives in moderate yields.     

Emulsifier-free emulsion polymerization of tetrafluoroethylene by radiation. III. Simultaneous formation of hydrofluoric acid

Simultaneous formation of hydrofluoric acid (HF) in the radiation-induced polymerization of tetrafluoroethylene (TFE) was investigated. HF concentration in PTFE latex was determined mainly by conductometric titration with 0.01 and 0.001N NaOH. The amount of HF formed is almost independent of agitation speed and the amount of n-hexadecane added and is maximal at ca. 70°C corresponding to the rate of polymerization. The rate of HF formation increases with the initial pressure of TFE monomer and dose rate and decreases with polymerization or TFE consumption. This fact suggests that HF is formed mainly by TFE reactions and not by the degradation of PTFE. The mechanism of HF formation in this reaction system in the absence of oxygen is shown in the following two schemes: scheme I is the reaction of TFE with primary radicals (OH·, H·, e) from the radiolysis of water; scheme II is the reaction of water with the species from the radiolysis of TFE. On the assumption that HF is formed only according to scheme I, the G value of HF formation G(HF)_calc can be calculated as 11.25. All observed G values G(HF)_obs are larger than G(HF)_calc. When the polymerization is carried out at 20 kg/cm² under various dose rates, G(HF)_obs increases with the dose rate. When the polymerization is carried out at 3.0 × 10⁴ rad/hr under various pressures, G(HF)_obs decreases with the decrease in pressure from 20 to 2 kg/cm² and is fairly close to G(HG)_calc at 2 kg/cm². This indicates that HF formation is due mainly to scheme II at high pressure (in the presence of enough TFE) and to scheme I as the pressure is lowered.