ИСТИНА

A challenging problem of carbon dioxide (CO2) capture and storage attracts a wide attention of scientists worldwide. СО2 separation from mixtures with nitrogen (N2) is an important aim in the processes of post-combustion CO2 capture from power plant flue gas. Moreover an actual problem is purification of energy carriers particularly of hydrogen synthesized in petrochemical and biochemical processes. Hydrogen produced in such processes contains small amounts of CO2 not over 20% and in this case it is technologically more favorable to use membranes which are selective to CO2. Glassy polymers attract high interest as materials for gas separation membranes. However most of membranes from glassy polymer either have selectivity toward hydrogen (polyimides, polysulfones etc.) i.e. work by a principle of high hydrogen diffusion due to small size of H2 atom or have selectivity toward CO2 (cellulose acetate) but extremely low values of permeabilities. As concerning separation of CO2/N2 mixture the aim for glassy polymers also consist in achievement of high selectivities and high permeabilities at the same time. Polyvinyltrimethylsilane [PVTMS] is one of the representatives of silicon-containing glassy polymers and represents high permeabilities, in particular CO2 permeability, but has small CO2 selectivities in mixture with N2 and nonselective toward CO2/H2 mixture. One of the ways to improve permselectivity is to enhance selectivity of CO2 solubility. This can be achieved by introducing polar ethylene oxide (EO) groups which are known to have high solubility toward CO2. Combination of poly(ethylene glycol) [PEG] and PVTMS properties looks perspective for creation of materials with high CO2 selectivity and high permeability. A two-stage method of synthesis of PVTMS-graft-PEG which includes synthesis of brominated polymer and subsequent substitution of bromine group by low molecular weight poly(ethylene glycol) ether was elaborated. PVTMS-graft-PEG samples with PEG content varied from 7 to 79% wt. were synthesized using the developed method. Solubility of graft-copolymers become worse with increase of PEG-content and it is difficult to prepare films from copolymer when PEG content is higher than 30%wt. It was shown what 30%wt. of PEG in graft-copolymer is not enough for appearance of CO2 solubility properties which were expected. So preparation of physical blends of PVTMS as well as PVTMS-graft-PEG with low molecular weight PEG were considered in order to increase content of EO groups in developed materials and to keep film forming properties. A new compound, namely poly(etheleneglycole) methyl(trimethylsilylmethyl) ether (MPEG), was synthesized on the basis of low molecular weight poly(ethelene glycol) methyl ether (PEGME) and chloromethyltrimethylsilane (CMTMS) for better compatibility of PEG with polymer. This compound is similar Si-containing fragment of elementary unit of polymer modified by EO groups. The degree of compatibility of obtained physical blends on the basis of PVTMS as well as PVTMS-graft-PEG with MPEG was estimated by method of DSC analysis. It was found that compatibility of MPEG with graft-copolymers is better than with pure PVTMS and it depends on the content of PVTMS-graft-PEG. According to the results the influence of EO groups content and method of their introduction (chemical modification and physical blending) in PVTMS on ability to reversible interaction with CO2 was shown. Gas transport properties and CO2 sorption of graft-copolymers and blends were studied. It was found that it is possible to turn selectivity toward CO2 in mixture with H2 in comparison with nonselective pure PTMSP and to enhance CO2/N2 selectivity several times by using designed membrane materials on the basis of PVTMS and PEG.