T. K. Meleshko

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.

Sorption and transport of aqueous isopropanol solutions in polyimide-poly(aniline-co-anthranilic acid) composites

Separation of aqueous isopropanol solutions by pervaporation using membranes based on composites of a polyimide with an aniline-anthranilic acid copolymer was studied.

Fullerene-Modified Polyimide Derived from 3,3',4',-Benzophenonetetracarboxylic Acid and 3,3'-Diaminobenzophenone for Casted Items and Its Use in Tribology

The possibility was examined of processing into a casted item (molding) of the crystallizing thermoplastic polyimide derived from 3,3-diaminobenzophenone and 3,3,4,4-benzophenonetetracarboxylic dianhydride and of composites of this polyimide with fullerenes. The tribological characteristics of the moldings were studied.

The study of sorption and transport properties of membranes containing polyaniline

The transport properties of membranes based on polyimide-polyaniline composites are studied in the pervaporation separation of a methanol-toluene binary azeotropic mixture. The morphology of the membranes is investigated by electronic microscopy, and the wettability of their surface is analyzed by contact-angle measurements. Special attention is given to the study of sorption and diffusion characteristics of membranes affecting the selectivity and rate of membrane separation. It is found that the incorporation of polyaniline into the matrix of the aromatic polyimide facilitates a reduction in the density of the composites relative to that of the nonmodified polyimide. It is shown that the membranes based on the polyimide-polyaniline composites are more selective with respect to methanol and show lower permeability during pervaporation of the methanol-toluene mixture than polyimide membranes.

Conducting film-forming composites based on polyaniline-polyimide blends

A procedure is developed for preparing conducting films by their casting from polymer solutions containing polyaniline in the form of a protonated emeraldin base and polyimides in two cosolvents, N-methylpyrrolidone or m-cresol. Self-supporting films cast from composites based on polyimides and camphorsulfonic acid-protonated polyaniline combine a conductivity of 10−1−10−2S/cm with good mechanical properties: elastic modulus E = 2.0−2.4 GPa, breaking strength σb = 55−60 MPa, and elongation at break ɛb = 8−10%. It has been shown that, when m-cresol and N-methylpyrrolidone are used as cosolvents, the maximum film conductivity is achieved at polyaniline amounts in the composites of 20 and 3%, respectively. In the latter case, films with good strength parameters are formed.

Study of the mechanism of the thermochemical reaction of polyimides with hydroxyl groups via vibrational-spectroscopy and quantum-chemistry methods

The thermochemical transformation of polyimides with one hydroxyl group in a diamine fragment that leads to changes in the polymer structure is studied. It is found that in an inert atmosphere in the temperature range 400–450°C, an intramolecular thermochemical reaction accompanied by evolution of carbon dioxide occurs. The FTIR spectra of all studied polyimide films prepared from different solvents and annealed in an inert atmosphere in the range 25–450°C show similar changes that do not agree with the structures of the reaction products (polybenzoxazole and polydehydrocyclobutabenzene) described in the literature. Possible reaction paths are calculated via quantum-chemistry methods. A mechanism of the intramolecular thermochemical transformation and the related structure of the formed polymer (aromatic lactam) are proposed.

New approach to the formation of polyimide ultrafiltration membranes involving modified polyacrylonitrile

A new approach to the formation of asymmetric ultrafiltration membranes based on insoluble rigid-chain aromatic polyimide (PI) and involving polyacrylonitrile modified by partial cyclization (m-PAN) has been studied. It has been found that m-PAN exerts a favorable effect on the membrane formation and composition: it (i) promotes fast precipitation at the stage of wet formation; (ii) acts as an imidization catalyst that allows for decreasing temperature at the stage of solid-phase thermal imidization; and (iii) it remains as a full-fledged component in the PI/m-PAN membrane. It was shown that up to 20 wt % m-PAN can be effectively introduced into the membrane composition. The membranes have been calibrated using a model mixture of proteins with different molecular weights. The structure, permeability to water, and thermomechanical properties of the membranes have been studied.

Film Composites of polyimide with polyaniline and poly(aniline-co-anthranilic acid)

New two-component composite polymer films are prepared and studied in terms of thermal stability and stress-strain properties. The matrix component of the composite is polyimide based on 3,3′,4,4′-(1,3-diphenoxybenzene)tetracarboxylic dianhydride and 4,4′-bis(4″-aminophenoxy)diphenyl sulfone. Another component is polyaniline or the copolymer poly(aniline-co-2-aminobenzoic acid). Composite films are cast from mixed solutions of individual polymers in N-methyl-2-pyrrolidone. Interpolymer interactions in polyimide composites with polyaniline or the copolymer of aniline and 2-aminobenzoic acid are investigated via viscometry and IR spectroscopy. The thermal treatment of composite films with poly(aniline-co-2-aminobenzoic acid) results in decarboxylation of the copolymer and formation of polyimide-polyaniline composite films. The morphology, microphase structure, and porosity of the composite films are different from those of the films cast from solutions of polyimide-polyaniline mixtures.

Preparation and structure of poly(4,4′-oxydiphenylene)pyromellitimide asymmetric ultrafiltration membranes

A process was developed for preparing asymmetric ultrafiltration poly(4,4′-oxydiphenylene)pyromel litimide membranes, involving wet forming of the membranes from the prepolymer, followed by catalytic solidphase thermal transformation of the prepolymer into the polyimide. The influence exerted on the structure and characteristics of the membranes by the compositions of the forming solution and precipitation bath, and also by thermal imidization conditions was examined. The optimal conditions were determined for preparing asymmetric ultrafiltration poly(4,4′-oxydiphenylene)pyromellitimide membranes exhibiting the water permeability coefficient of (10−500) × 10−6 m3 m−2 s−1 atm−1 and molecular weight cut-off in the range (5−100) × 103 g mol−1.

Features of the crystal structure of the polyimide derived from 3,3'-diaminobenzophenone and 3,3', 4,4'-benzophenonetetracarboxylic dianhydride

Changes occurring in the structural organization of the thermoplastic polyimide derived from 3,3-diaminobenzophenone and 3,3,4,4-benzophenonetetracarboxylic dianhydride on heat treatment at temperatures in the range 250-350°C were studied, and the influence of these changes on the rheological behavior of the polymer was examined.