Direct fluorination of polymers is a widely utilized technique for chemical modification. Such introduction of fluorine into the chemical structure of polymeric materials leads to laminates with highly fluorinated surface layer. The physicochemical properties of this layer are similar to those of perfluorinated polymers that differ by a unique combination of chemical resistance, weak adhesion, low cohesion, and permittivity, often barrier properties, etc. Surface modification by elemental fluorine allows one to avoid laborious synthesis of perfluoropolymers and impart such properties to industrial polymeric materials. The current review is devoted to a detailed consideration of wetting by water, energy characteristics of surfaces, adhesion, mechanical and electrical properties of the polymers, and composites after the direct fluorination.

Fluorine-containing polymers occupy a peculiar niche among conventional polymers due to the unique combination of physicochemical properties. Direct surface fluorination of the polymeric materials is one of the approaches for the introduction of fluorine into the chemical structure that allows one to implement advantages of fluorinated polymers in a thin layer. Current review considers the influence of the surface interaction of the polymeric materials and membranes with elemental fluorine on gas, vapor and liquid transport as well as swelling and related phenomena. The increase in direct fluorination duration and concentration of fluorine in the fluorination mixture is shown to result mostly in a reduction of all penetrants permeability to a different extent, whereas selectivity of the selected gas pairs (He-H₂, H₂-CH₄, He-CH₄, CO₂-CH₄, O₂-N₂, etc.) increases. Separation parameters for the treated polymeric films approach Robeson’s upper bounds or overcome them. The most promising results were obtained for highly permeable polymer, polytrimethylsilylpropyne (PTMSP). The surface fluorination of rubbers in printing equipment leads to an improved chemical resistance of the materials towards organic solvents, moisturizing solutions and reduce diffusion of plasticizers, photosensitizers and other components of the polymeric blends. The direct fluorination technique can be also considered one of the approaches of fabrication of fuel cell membranes from non-fluorinated polymeric precursors that improves their methanol permeability, proton conductivity and oxidative stability.

Poly-2,6-dimethylphenylene oxide (PPO) film samples with varying degrees of crystallinity (from 0 to 69%) were obtained by means of different techniques. The films were studied by various physicochemical methods (Fourier-transform infrared spectroscopy, positron annihilation lifetime spectroscopy, X-ray diffraction, and ¹H nuclear magnetic resonance relaxation). Solubility coefficients of gases in the PPO samples were measured via sorption isotherms of gases by volumetric technique with chromatographic detection. The apparent activation energy of permeation and the activation energy of diffusion of all gases were estimated based on temperature dependences of gas permeability and diffusivity for amorphous and semi-crystalline PPO in the range of 20–50 °C. The peculiarities of free volume, density, and thermal properties of gas transport confirm the nanoporosity of the gas-permeable crystalline phase of PPO. So, the PPO can be included in the group of organic molecular sieves.

The influence of controlled biaxial uniform deformation of annealed and unannealed (with residual solvent) Ultem 1000 amorphous glassy polyetherimide films on their mechanical and gas separation characteristics have been studied. It has been shown that the transport and mechanical properties of strained Ultem-1000 film samples can be examined on reaching the quasi-steady state 48 hours after the beginning of their deformation. It has been shown that an increase in the strain of the unannealed Ultem 1000 films leads to an increase in mechanical strength of the films (increase in elastic modulus, tensile strength, and upper and lower yield stresses and decrease in elongation at break), an increase in chain packing density, and orientation of chains in the dense part of the polymer matrix, with these changes resulting in a drop of gas permeability and an enhancement of ideal selectivity. It has been demonstrated that the deformation of the annealed Ultem films leads to a dramatic change in mechanical properties even at small strains: from brittle fracture to the emergence of plastic deformation. As the strain increases, the gas diffusion coefficients decrease for all the samples, suggesting the ordering of chain packing. Thus, the combination of the methods used has made it possible to obtain information about the effects of deformation of polymer films and the residual solvent on their structural and transport properties useful for achieving the best permeability–selectivity ratio.

Membrane gas separation using polymeric membranes is one of rapidly developing energy-conserving technologies. This review describes the scope of membrane gas separation problems and demonstrates the relevance of membrane methods for their solution. The basic concepts and regularities of diffusion gas transfer and principles and characteristics of membrane gas separation are considered. The main physicochemical approaches to the selection of membrane materials considering both the properties of the gas–polymer system and the structure and physical properties of polymers are discussed. The considered issues are combined within a common approach to substantiate the choice of both existing commercial polymers and advanced polymeric materials to address important gas separation problems such as separation of air components; carbon dioxide, hydrogen and helium recovery from natural and industrial gas mixtures; and separation of a nitrogen and methane mixture. The avenues of development of the membrane materials science to solve each of the mentioned problems of membrane gas separation are demonstrated. The review is intended for specialists in the synthesis and physics of polymers for planning the research and assessing the applicability of polymeric materials for various practical gas separation problems and for specialists in the membrane materials science and membrane technology. The bibliography includes 165 references.