A. E. Chalykh

Water sorption on and water diffusion in chitin and chitosan

The kinetics of the sorption of water vapor on powders of crab-shell chitin and chitosan are studied via the methods of static sorption, thermography, and X-ray structural analysis. Sorption isotherms are obtained in the range of humidity from 10 to 95%. S-Shaped water-sorption isotherms observed for all chitin and chitosan samples are approximated via superpositioning of Langmuir and Flory-Huggins isotherms. The water-polysaccharide interaction parameters and the maximum sorption capacities of water located in chitin and chitosan are determined. The cluster integral is calculated, and the moisture values corresponding to water-cluster formation are determined. The water-diffusion coefficients are determined, and the effective activation energies of water diffusion are estimated: 70 kJ/mol in chitosan and 60 kJ/mol in chitin. The data on the concentration dependences of the coefficients of diffusion of water in the powdered chitin and chitosan are summarized.

Phase equilibrium and interdiffusion in the oligo(3,3-bis(azidomethyl)oxetane)-oligo(3-methyl-3-azidomethyloxetane) system

Intersolubility and interdiffusion in the oligo(3,3-bis(azidomethyl)oxetane)-oligo(3-methyl-3-azidomethyloxetane) binary system are studied. The components of the system differ in symmetric and non-symmetric positions of azide groups along the polymer chain, respectively. The chemical and conformational features ensure the ability of oligo(3,3-bis(azidomethyl)oxetane) to crystallize at temperatures of ∼50°C. The system of azidooxetane oligomers is characterized by a simple crystalline equilibrium crystal-melt. The generalized phase diagram of the binary system is constructed. The interdiffusion zones of oligomers are analyzed in detail in a wide temperature range, and a number of specific effects manifesting themselves during their intersolubility are observed. The concentration and temperature dependences of diffusion coefficients are examined, and the activation energies of diffusion are calculated.

Residual water in polyvinyl alcohol

The state of sorbed water molecules in the matrix of polyvinyl alcohol is investigated via the methods of static sorption, DSC, TGA, IR Fourier spectroscopy, 1H NMR spectroscopy, and quantum-chemical simulation. It is shown that the sorption of water by polyvinyl alcohol characterized by an S-shaped isotherm is described by the double-sorption model. It is established that the low diffusion coefficients and extremely low rates of desorption processes observed in the range of low activities are determined by a shift of the equilibrium toward the formation of hydrogen-bonded complexes of water molecules with hydroxy groups of the polymer. A mechanism for the behavior of residual water in hydrophilic polymers is suggested. It implies that differences between polymers are determined only by the quantity of residual water immobilized in “traps” and the energy of hydrogen-bond formation.

Phase diagrams of blends of azide-containing polyoxetanes

The mutual solubility of polymers based on the azide-containing oxetane monomers 3,3-bis(azidomethyl)oxetane and 3-azidomethyl-3-methyloxetane is studied. The temperatures of melting, crystallization, glass transition; the upper critical solution temperature; and the compositions of coexisting phases for blends of polymers with different molecular masses are determined via differential scanning calorimetry and multiple-beam microinterferometry. On the basis of these data, the phase diagrams of blends are constructed. The melting regions and the metastable and heterogeneous states are determined. The studied systems are shown to have a complex amorphous-crystalline equilibrium and to differ in the location of boundary curves on the phase diagram, depending on the molecular mass of the components. Amorphous separation below the liquidus line in the metastable region with respect to the crystalline equilibrium is experimentally detected. The motion of the figurative point in different regions of the diagram is thoroughly considered. The specifics of structural and morphological organization of systems are examined via electron microscopy.

Interdiffusion in a polystyrene-poly(vinyl methyl ether) system

Interdiffusion in polystyrene-poly(vinyl methyl ether) systems is studied by optical-interferometry method in wide temperature and concentration ranges. For these systems, temperature-concentration dependences are constructed, activation energies are calculated, and dependences of the diffusion coefficient on the molecular mass of polystyrene are examined. The results are compared with the phase diagrams of the systems, and it is shown that the diffusion coefficient decreases as the binodal curve is approached, thereby leading to corresponding changes in the Arrhenius coordinates.

A study of the thermal degradation of poly(vinyl chloride)

A thermal degradation of poly(vinyl chloride) (PVC) was studied. This was an essential step in the investigation of the compatibility of PVC-based systems because mixing in industry and in the preparation of materials is carried out in the viscous flow range close to thermal degradation.

Surface-energy characteristics of films of molecular brushes based on polyimide and poly(methyl methacrylate)

Surface characteristics of film samples of molecular brushes with a polyimide backbone and PMMA side chains, as well as of films of polyimide constituting the backbone and linear PMMA homopolymers obtained via the selective destruction of the polyimide backbone of these brushes, are investigated for the first time. The surface-energy characteristics of the films of molecular brushes are determined by the structure and conformational state of the PMMA side chains. The conformations of molecular brushes possessing a polyimide backbone well screened by side chains are preserved after the transition from solutions to “dry” copolymer films and are characterized by high stability. The observed surface activity of molecular brushes is due to adhesion interactions with functional groups of the substrate. The difference in surface activities is caused by small-scale conformational changes in the side chains of molecular brushes. A globular core of molecular brushes formed by the polyimide backbone remains practically spherical and probably does not change in volume.

Analytical electron microscopy for the structural study of grafted polymers

A procedure for the selective staining of phenyl groups of PS and the formation of sulfoacidic groups is proposed. For PE with grafted PS, the combined use of scanning and transmission electron microscopy and X-ray microanalysis in the proposed procedure for staining and structural etching of cross sections in high-frequency oxygen discharge plasma makes it possible to gain information about the distribution of grafted PS in the cross section of the material and the phase state of the system. In grafted polymers, diffusion coefficients of sulfuric acid are estimated. The duration of staining is calculated. The X-ray microanalysis allows a quantitative estimation of the ratio between sulfoacidic groups and sulfonic bridges between phenyl groups.

The Structure of Individual Macromolecules of Butadiene-Styrene Copolymers in Polystyrene Matrix

Radial-density distribution functions of segments and radii of gyration are obtained for the first time with the example of systems of statistical butadiene–styrene rubber of different composition and polystyrene by the processing of electron-microscopy images of individual copolymer molecules. Linear correlation dependences of R = f(M1/2) are plotted. The possibility of quantitative determination of fluctuation deviation from the equilibrium radius value is demonstrated. A method of calculating the values of Flory–Huggins parameters for individual macromolecules and their assembly is suggested.

Phase equilibria in a polyethylene–polystyrene system

The method of optical interferometry is used to study the interaction of PE with PS in situ. On the basis of the obtained data, phase diagrams of the PE–PS system are constructed for a number of molecular masses of the components. For PE and PS oligomers, the UCMT values are determined. Pair parameters for the interaction of homopolymers are calculated, and their dependences on temperature and molecular mass are considered. The quantitative analysis of the behavior of high-molecular-mass fractions of PE and PS at high temperatures is carried out, and the regions of a partial compatibility of the components are predicted.