S. V. Kononova

Polymer-inorganic nanocomposites based on aromatic polyamidoimides effective in the processes of liquids separation

The polymer-inorganic nanocomposites based on the aromatic polyamidoimides and the silicate nanotubes of chrysotile structure were developed. The polyamidoimides were synthesized from dicarboxyphenylphthalimide dichloride by the polycondensation with either 4,4′-diaminodiphenyl ether or 3,5-diaminobenzoic acid. The morphology, mechanical and transport properties of the nanocomposite films were studied. Distribution of nanotubes in the composites is shown to be defined by the chemical structure of the polyamidoimide. The conditions for the formation of the composites were optimized to provide a significant increase in selective permeability toward alcohol and water in the process of pervaporation at the introduction of the nanotubes in the polymer.

Nanocomposites Based on Aromatic Polyamide-Imide and Magnesium Hydrosilicate Nanotubes

Structure, morphology, and thermal properties of nanocomposites based on thermally stable poly(diphenyloxydamide-N-phenylphtalimide) (PAI) and layered magnesium hydrosilicate nanotubes (NTs) were studied using thermogravimetric analysis, dynamic mechanical analysis, atomic force microscopy, and differential scanning calorimetry. Thermal stability and glass transition temperature of the composites were shown to exceed those of the PAI matrix. Introduction of NT into the polymer matrix appreciably increased the elasticity and deformability of the composite material. The content of NT was also shown to greatly influence the surface morphology of the PAI-NT composites.

Aromatic polysulfone imides and membranes based on them

Aromatic polyimides containing diphenyl sulfone fragments in the backbone were prepared. Asymmetric microporous films of the synthesized polymers were prepared by wet forming under the conditions of a phase-inversion process. The morphologies and the mechanical and transport properties of nonporous and phase-inversion films as materials for pervaporation membranes were studied. Multilayer composite membranes with diffusion layers of an aromatic polyether imide were prepared on the basis of microporous polyamido imide films. These membranes showed high performance in pervaporation separation of ethanol-cyclohexane mixtures of various compositions.

Pervaporation multilayer membranes based on a polyelectrolyte complex of λ-carrageenan and chitosan

A polyelectrolyte complex (PEC) was prepared from chitosan (CS) and λ-carrageenan (λ-CAR) using a layer-by-layer deposition of polyion solutions on a plated nonporous support. This material was then used as a multilayer membrane for the pervaporation separation of aqueous ethanol solutions. The fabricated complex film (25-30μm thick) was a multilayer system (λ-CAR-PEC-CS) containing a polycation CS (MW 3.1×105, DDА 0.93), a polyanion λ-CAR (MW 3.5×105, extracted from the alga Chondrus armatus), and a PEC layer formed between the two polyion layers. X-ray diffraction indicated a significant structuring of the film in the region of the composite PEC-CS bilayer. The structural and morphological characteristics of the CS surface in the multilayer membrane, as revealed by atomic force microscopy, were close to the characteristics of the dense CS film. However, this structure changed following pervaporation (i.e., the distinct spherical structures on the surface disappeared). Similarly, the initially loose surface of λ-CAR in the composite changed to an ordered domain after pervaporation. The transport properties of the pervaporation membranes were tested by examining the separation of ethanol-water mixtures of different compositions. The flux increased with an increase in the weight percentage of water in the feed mixture, but the separation capacity of the membrane was unchanged. In a range of feed concentrations of 50-94wt%, the membrane mainly releases water with a corresponding concentration in the permeate of 99.9-99.8wt% and substantial fluxes of 0.003-1.130kgm-2h-1 at 40°C. The obtained results indicate significant prospects for the use of non-gelling type CARs for the formation of highly effective pervaporation membranes.

Low-voltage scanning electron microscopy of multilayer polymer systems

The possibilities of low-voltage scanning electron microscopy for visualization of specific features of the microstructure in internal layers of multilayer polymer films are demonstrated by the example of “chitosan–polyelectrolyte complex–alginic acid” composite. The process of electron beam interaction with a sample at low electron energies is considered. The key parameters of low-voltage electron microscopy, which make it possible to increase the resolution of SEM images of polymer systems, are discussed.

Phase-inversion gradient-porous films on the basis of polyamidoimides derived from phthalimidobenzenedicarbonyl dichloride and various diamines

Morphology of microporous films prepared from aromatic polyamidoimides under different molding conditions was studied by scanning, transmission, and atomic force microscopy with the specific attention given to the nanosize skin layer. The films were manufactured by the phase inversion molding of aromatic polyamidoimides which were synthesized by low-temperature polycondensation of phthalimidobenzenedicarbonyl dichloride with various diamines. Comparison of the parameters of films, including their wettability and X-ray photoelectron spectroscopy data, gave additional information on factors affecting the mechanism of formation of microporous membranes in the system polymer (polyamidoimide)-solvent (N-methylpyrrolidin-2-one)-non-solvent (water).

Structure, morphology, and thermal properties of nanocomposites based on polyamido imide and hydrosilicate nanotubes

New nanocomposites based on heat-resistant poly[(diphenyl oxide)amido-N-phenylphthalimide] with Mg3Si2O5(OH)4 hydrosilicate nanoparticles of tubular structure were prepared. The structure, morphology, and thermal properties of the nanocomposites were studied in relation to the content of hydrosilicate nanotubes.

Morphology and mechanical properties of polymer-inorganic nanocomposite containing triple chain fibrous Na-Mg hydrosilicate

A polymer-inorganic nanocomposite of fibrous Na-Mg triple chain hydrosilicate and polyamidoimide based on 4-chloroformyl-(N-p-chloroformylphenyl)phthalimide and 4,4′-diaminodiphenyl ether has been developed. Morphology and dynamic mechanical properties of the nanocomposite films have been studied. Anisotropy of mechanical properties of the nanocomposite and the pristine polyamidoimide films has been revealed. Introduction of the fibrous filler disrupts the ordered mesomorphic structure of the polymer matrix; its recovery upon heating above the glass transition temperature is possible.

Composites of multiblock (segmented) aliphatic poly(ester imide) with zirconia nanoparticles: Synthesis, mechanical properties, and pervaporation behavior

On the basis of pyromellitic dianhydride, p-phenylenediamine, and poly(butylene adipate) diol (M n = 1 × 103) and poly(ethylene adipate) diol (M n = 1 × 104) taken at a molar ratio of 10 : 1, initial samples of multiblock poly(ester imide) and its composites with nanoparticles of two types—zirconia ZrO2 surface-treated with γ-aminopropyltriethoxysilane and zirconia doped with yttria (Y0.03Zr0.97O1.985)—are synthesized. Nanoparticles are introduced into the polymer matrix at the stage of synthesis of the poly(ester imide) prepolymer. The mechanical properties of films of poly(ester imide) and its nanocomposites are determined under static and dynamic testing conditions, and the permeabilities and separation selectivities of corresponding solid films for mixtures of aromatic and aliphatic hydrocarbons (toluene-n-octane and benzenecyclohexane) of various compositions are measured under pervaporation testing conditions. It is shown that the different mechanical and pervaporation properties of film samples are due to the presence of zirconiabased nanoparticles.

Polymorphic Modifications of Chitosan

This work describes the analysis of the crystal structures of chitosan, its main polymorphic modifications, and its characteristic mutual chain packing and hydrogen bond systems in the crystalline regions of conformers. The analysis takes into consideration the crystal structures of chitosan complexes (salts) with organic and inorganic acids and their structural transformations. Notably, the transformation of the hydrated form of chitosan into anhydrous is found to be irreversible and occurs either at high temperatures or through a less stable form of hydrated salts. The interaction with polyanions during the formation of multilayer films can be considered as a way to form the anhydrous crystalline form of chitosan.