G. A. Polotskaya

Transport of Small Molecules through Polyphenylene Oxide Membranes Modified by Fullerene

Abstract Homogeneous membranes based on fullerene‐polyphenylene oxide compositions containing up to 2 wt% fullerene C60 were prepared. The effect of fullerene addition on PPO transport properties was studied in gas separation and pervaporation processes. Permeability coefficients of H2, O2, N2, CH4, and CO2 were measured; a correlation between gas transport properties and membrane free volume was established. Pervaporation properties were studied for the system with ethyl acetate synthesis reaction: quaternary system ethanol—acetic acid—water—ethyl acetate and some constituent binary and ternary mixtures. Pervaporation in binary systems, ethanol–water and ethyl acetate–water was considered with the use of the data on sorption capacities and interaction parameters. In pervaporation of a quaternary reacting mixture, the permeate containing essentially ethyl acetate was obtained. Results show that membranes with fullerene additives exhibit improved transport properties.

Gas transport and structural features of sulfonated poly(phenylene oxide)

The effect of ionomer structure on gas transport properties of membranes was investigated. For this purpose physical and transport properties of poly(phenylene oxide) (PPO) and its sulfonated derivative (SPPO) were compared. SPPO has a more rigid structure and a lower free volume, which determines low gas permeability and high permselectivity. Gas transport properties of two types of SPPO—PPO composite membranes with top layers prepared from solutions in methanol or N,N-dimethylacet-amide (DMA) were investigated. The use of SPPO solution in DMA leads to the formation of membranes with higher gas permeability. It was shown that DMA is a morphologically active solvent for SPPO. Strong complexes of SPPO with DMA are formed in solution and retained upon transition into the condensed state. The plasticizing effect of DMA on SPPO determines the high gas permeability of the membranes and is in agreement with their mechanical properties.

Polyamide Membranes Modified by Carbon Nanotubes: Application for Pervaporation

New polymer nanocomposites consist of poly(phenylene isophtalamide) (PA) modified by carbon nanotubes (CNT) were obtained by the solid state interaction method to prepare dense membranes. The investigation of the PA/CNT nanocomposites was made by Raman spectroscopy. The morphology of the dense membrane was analyzed by SEM. The transport properties of the dense polyamide membranes modified by 2 and 5 wt% CNT were studied in pervaporation of methanol/ methyl tert-butyl ether mixture. It was shown that the selectivity with respect to methanol and permeability were the highest for membranes containing 2 wt% CNT as compared to membranes of pure PA and containing 5 wt% CNT. To analyze transport properties the sorption tests and contact angle measurements were employed.

Effect of polymerization conditions of pyrrole on formation, structure and properties of high gas separation thin polypyrrole films

Abstract Gas separation membranes composed of sulfonated poly(phenylene oxide) as a support and polypyrrole were prepared by two alternative ways: (1) the support films were saturated by oxidant and then treated with pyrrole vapor; (2) the support films were saturated with pyrrole vapor and then treated with the oxidant. Study of the polymerization conditions has shown that the second method of membrane preparation results in formation of a dense polypyrrole layer on the support surface. The membranes were characterized by Fourier transform infrared spectroscopy, ultraviolet spectroscopy, optical microscopy and atomic force microscopy. Measurements of gas transport properties demonstrated that the O 2 vs. N 2 selectivity coefficient of this polypyrrole layer was 15, which is one of the highest values described in the literature.

Gas-separating properties of membranes based on star-shaped fullerene (C60)-containing polystyrenes

Based on regular star-shaped PSs differing in the structure of the branching center (one or two covalently bound fullerene C60 molecules) and in the number of branchings (6 and 12), homogeneous gas-separation membranes have been produced. The transport behavior of the membranes with respect to several gases, such as H2, He2, N2, CO, CO2, and CH4, has been studied by mass spectrometry. It has been found that the membranes prepared from six-arm PSs are characterized by a smaller density of macromolecular packing than the membranes obtained from 12-arm PCs and, consequently, they possess higher gas permeability. The starshaped PSs demonstrate a higher selectivity factor for separation of the O2/N2 gas pair compared to the corresponding characteristics of the linear PSs. The analysis of gas-separation characteristics by means of the Reitlinger-Robeson diagrams demonstrates that the transport behavior of star-shaped PSs qualitatively surpasses similar parameters of the known polymers in the separation of the CO/N2 gas pair.

Effect of molecular weight parameters on gas transport properties of poly(2,6-dimethyl-1,4-phenylene oxide)

The gas permeability of O 2 and N 2 for homogeneous and composite membranes prepared from poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) samples with different molecular weight parameters was investigated. Temperature dependencies of gas permeability coefficients and permselectivity were determined for homogeneous membranes. It was established that gas permeability coefficients of homogeneous membranes depend on molecular weight of the polymers used. The gas permeability of composite membranes with a PPO selective layer was investigated as a function of PPO intrinsic viscosity [η] and its casting solution concentration (c). It was shown that under the condition [η].c = const it is possible to obtain composite membranes with the same transport properties by using polymers with different molecular weight parameters.

Gas transport properties and structural order of poly(4,4′-oxydiphenylene piromelliteimide) in composite membranes

Abstract Specific physico-chemical properties of aromatic polyimides determine their high selectivity in gas separation and relatively low gas permeability. Gas transport properties of insoluble polyimides may be improved in the process of membrane formation. A two-stage process was used for making composite membranes comprised of poly(4,4′-oxydiphenylene pyromelliteimide) (PI) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO). In the first stage the polyamic acid (PAA)/PPO membrane was formed by casting a 5% PAA solution on the surface of the PPO support. The second stage of solid-phase imidization led to obtaining a PI/PPO membrane. Catalytic, chemical and thermal methods of imidization with heating to 150°C were compared. It was established that the catalytic method is the simplest and most reliable in the preparation of membranes with the best gas transport properties. The interaction between the PAA prepolymer and benzimideazole (BI) catalyst was studied. The formation of a PAA:BI complex is favourable to imide ring formation at lower temperature. The PI/PPO membrane was analysed on the basis of the resistance model. It was shown that resistance to gas flow through the PI/PPO composite membrane is determined principally by the zone of homogeneous film in the PI top layer. The analytical data on the membrane structure was verified by electron microscopy data. It was concluded that low-temperature solid-phase catalytic imidization is a promising method for making composite membranes based on insoluble polyimides.

Formation and analysis of a polyimide layer in composite membranes

Composite membranes containing a thin-film layer of aromatic polyimides (PI) ensure an advantageous combination of selectivity and permeability in gas separation. A series of rigid-chain PI with different chemical structures were studied as a thin active layer. Composite membranes were prepared by coating a solution of poly(amic acid) (PAA) and an imidization catalyst on a poly(phenylene oxide) (PPO) support with pores filled by decane. The subsequent stage of solid-state catalytic transformation of the PAA/PPO membrane into the PI/PPO membrane determines the specific structure of the PI layer and the transport properties of the PI/PPO composite membranes. The structure of composite membranes was determined by scanning electron microscopy and analyzed in the terms of the resistance model of gas transport in composite membranes.

Fullerene‐Containing Polymer Membranes for Rejection of Estrogenic Compounds in Water

Abstract Asymmetric membranes based on compositions of fullerene C60 and hydrophobic polymer, polyphenylene oxide containing up to 10 wt.% C60, were prepared with the aim of study on removing estrogenic pollutants from water. Efficiency of asymmetric membranes to estrone rejection was estimated in adsorption and ultrafiltration processes. Membrane containing 2 wt.% C60 showed the fastest adsorption rate in the limiting adsorption stage. In the dead‐end filtration, all kinds of membranes demonstrated very good estrone rejection (more than 95%). Fullerene‐containing membranes exhibited higher flux than pure polyphenylene oxide membranes.

Polyimide Ultrafiltration Membranes with High Thermal Stability and Chemical Durability

Abstract Asymmetric ultrafiltration membranes based on poly[(4,4′-oxydiphenylene)pyromelliteimide] were produced by wet technique from prepolymer casting solution, followed by solid-phase conversion of the prepolymer membranes into polyimide insoluble form at 200°C. It was demonstrated that by adding benzimidazole to the casting solution and filling of prepolymer membrane pores with inert high-boiling oil prior to thermal treatment allow us to prepare asymmetric porous polyimide membranes. The main characteristics of the membranes obtained (permeability coefficients and molecular weight cut-off) match those typical to ultrafiltration membranes. It was found that the developed asymmetric ultrafiltration polyimide membranes have excellent thermal and chemical resistance. The membranes retain rigidity above Tg (360°C) and are chemically stable at temperatures up to 400°C. The developed membranes are resistant against swelling and dissolving in aggressive and organic media including amide solvents.