ИСТИНА

Perfluorinated polymers form unique class of polymeric materials due to combination of various properties (low surface and cohesive energies, high chemical resistance, low electrical conductivity, high refraction index, etc.). Only a few of them can be successfully applied in gas separation because many perfluorinated polymers are semicrystalline and, hence, have low gas permeability. In this work, synthesis of new perfluorinated copolymers and investigation of their physicochemical and transport properties are considered. The copolymers (copoly-HFP-TFEs) of hexafluoropropylene (HFP) and tetrafluoroethylene (TFE) with intrinsic viscosities [η] = 0.62 and 1.099, respectively, were synthesized by radical polymerization of HFP and TFE at 280°C and 12 kbar with partial ratio of the comonomers 5:3 and 3:1. However, actual ratios of the comonomers in bulk polymers according to 19F NMR were equal to 0.92:0.08 and 0.95:0.05 respectively. The copolymers are amorphous, soluble in common perfluorinated solvents (perfluorodimethylcyclohexane, perfluorotoluene, perfluorobenzene) and have sufficient film-forming properties. According to DSC analysis, copoly-HFP-TFEs have glass transitions at 150-160°С. The densities of the copolymers determined by hydrostatic method are as high as 2.02 and 2.01 g/cm3. Permeability (P) and diffusion (D) coefficients of He, H2, O2, N2, CO2, CH4 were measured by Daynes-Barrer method on a Baratron barometric setup in the temperature range of 20-50°С. The upper stream pressure varied in the range of 1-3 atm, the downstream pressure was 0-12 Torr. Polymer films were prepared by casting its 2 w/w% solution in perfluorotoluene on a cellulose support and subsequent removal after evaporation of the solvent. Then, the films were annealed according to the following protocol (heating (5°C/min) up to 110°C, keeping for 3 h at this temperature, 130°C (3 h), 140°C (1.5 h), 160°C (1 h), 170°C (2 h) and subsequent cooling to the ambient temperature). Gas transport properties were determined for as cast and annealed samples of the copolymers. Annealing procedure results in a compactization of the samples so that the permeability coefficients of light gases (He, H2) decreased only slightly while the permeability and diffusion coefficients of larger penetrants are reduced significantly by a factor of 3-10 for different gases. On Robeson diagrams (ideal separation factor vs. permeability of more permeable gas) for He/CH4, CO2/CH4, H2/CH4, N2/CH4 the data points for copoly-HFP-TFEs lie on common lines formed by other perfluorinated polymers, located in the middle position near Hyflon AD60 and polyhexafluoropropylene (PHFP). Diffusion coefficients of gases in copoly-HFP-TFEs are lower than those in AF1600 by a factor of 1-1.6 but are comparable and slightly higher than diffusion coefficients of gases in Hyflon AD60, PHFP and Cytop. The same is true for solubility coefficients of gases calculated as P/D ratio. Thus, new perfluorinated copolymers of HFP and TFE were synthesized by radical polymerization at high pressure and temperature. The copolymers were shown to have moderate level of gas sorption, diffusivity and permeability among other perfluorinated polymers available, but at the same time they have quite favorable combination of permeability and ideal separation factors for gas pairs containing hydrocarbons.