Organosilica-Modified Multiblock Copolymers for Membrane Gas Separation.

Organosubstituted silica derivatives were synthesized and investigated as modifiers of block copolymers based on macroinitiator and 2,4-toluene diisocyanate. A peculiarity of the modified block copolymers is the existence in their structure of coplanar rigid polyisocyanate blocks of acetal nature (O-polyisocyanates). Organosubstituted silica derivatives have a non-additive effect on high-temperature relaxation and α-transitions of modified polymers and exhibit the ability to influence the supramolecular structure of block copolymers. The use of the developed modifiers leads to a change in the gas transport properties of block copolymers. The increase of the permeability coefficients is due to the increase of the diffusion coefficients. At the same time, the gas solubility coefficients do not change. An increase in the ideal selectivity for a number of gas pairs is observed. An increase in the selectivity for the CO2/N2 gas pair (from 25 to 39) by 1.5 times demonstrates the promising use of this material for flue gases separation.

Features of the Gas-Permeable Crystalline Phase of Poly-2,6-dimethylphenylene Oxide.

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 Effect of Conformation Order on Gas Separation Properties of Polyetherimide Ultem Films.

Changes of the spectral characteristics of absorption bands depending on the films' treatment method were registered for polyetherimide Ultem films. The possibility of selection of structural criteria (the ratio of the functional groups absorption bands intensities) showing all conformational changes in elementary unit with metrological processing of the results is shown. It is demonstrated that film formation from chloroform solution leads to elementary unit fragments, Ph-O-Ph', which have an effect on macromolecule conformation and result in increasing of space between fragments of macromolecules (local polymer matrix packing loosening). Desorption of residual chloroform from films by ethanol or supercritical CO2 leads to a change of conformers set in Im-Ph-Im' units. Quantum chemical modeling showed the possibility of convergence of these fragments in neighboring macromolecules, and consequently of interchain π-π interaction (local densification of chain packing of the polymer matrix). After annealing at a temperature higher than glass transition temperature, the polyetherimide film exhibits the most disordered (amorphous) state at all of the fragments. It is demonstrated that the results, obtained by the combination of theoretical and experimental vibrational spectroscopy methods, are in good agreement with data of chain packing ordering found by analysis of gas separation parameters.