I. P. Kim

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 Tb ≈ 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.

Determination of rate constants for radical telomerization chain growth and transfer from the molecular-mass distribution of oligomer

The ratio of rate constant for growth and transfer X(n), as a function of the chain length n has been found from the measured molecular-mass distributions of the products of tetrafluoroethylene telomerization in acetone, ethyl acetate, chloroform, and carbon tetrachloride. For all these telogens, the function increases by a factor of 1.5–2.5 in the range of n from 2 to 5, is almost constant for n of 6 to 10, and increases by a factor of 7–10 in the range of n from 12 to 20. This behavior of the function X(n) has been explained in terms of the model of diffusion-controlled propagation and kinetic chain transfer. The model takes into account the change in the diffusion nature of oligomers in the form of rigid rods with an increase in their length. A sharp increase in X(n) occurs when the oligomers that accumulate in the environment of growing macroradical sterically restrict the withdrawal of the forming oligomer to the bulk by an effective solid angle, which decreases with the increasing oligomer length and becomes minimal in the region of formation of colloidal particles.

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 C0 ≈ 0.5 mol/l. The MMD includes a low-molecular-mass component (n ≤ 5) in an amount that decreases with increasing C0 and a high-molecular-mass component, whose maximum shifts toward higher values of n with an increase in C0. The bimodality of MMD is explained in terms of decrease in the propagation rate constant with the accumulation of long oligomers.

Application of infrared spectroscopy to investigation of the structure of tetrafluoroethylene telomers in acetone and their intermolecular interaction

Measured FTIR spectra of the products of the radiation-chemical telomerization of tetrafluoroethylene in acetone have been compared with the spectra calculated by density functional theory for oligomers with the structural formula H(C2F4)nCH2COCH3, n ≥ 3, and the dimer of the latter. Inhomogeneous broadening, splittings, and shifts of the CH, CC, and CO vibration bands in the terminal groups on the oligomers relative to the associates of acetone molecules confirm the structural formula of the oligomers and show that strong hydrogen bonds are formed between their end groups.

Enthalpies of formation of radicals and the mass spectra of the products of tetrafluoroethylene polymerization in acetone

The mass spectra of the dissociative electron-impact ionization products of telomers formed upon the radiation-chemical telomerization of tetrafluoroethylene in acetone were measured over the range of m/z from 1 to 204. The most intense bands at m/z = 43, 51, and 57 were attributed to the CH3CO+, CF2H+ and CH3COCH2+ cations—the main dissociation products of the H(C2F4)nCH2COCH3 telomers. The telomer composition was consistent with a radical telomerization mechanism, in which chain growth and chain transfer are due to the formation of the CH3COCH2· radical. Based on published data supplemented with quantum-chemical calculations, the enthalpies of formation of the radicals R(CF2)n (n = 2–8; R = H, CH3, CH3CO, and CH3COCH2) were tabulated. The formation of telomers with the same terminal groups is consistent with thermodynamic data and a polymerization mechanism in which the chain growth reaction is diffusion-limited and the chain transfer reaction is activated hydrogen-atom transfer.

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

AbstractThe 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

The study of polymerization initiated by gamma-irradiated perfluoroacids and their derivatives

\bar n

Study of fluoroalkylsilanes, a new class of amphiphilic oligomers: Determination of end groups and chain length

≈ 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