V. K. Gerasimov

Sorption of water by poly(vinyl alcohol)

The isotherms of water sorption by poly(vinyl alcohol) have been obtained by static sorption methods in a wide range of vapor activities. The properties of poly(vinyl alcohol) at various values of relative humidity have been studied by DSC, X-ray diffraction analysis, and mechanical testing. It has been shown that the correct thermodynamic analysis of sorption isotherms for sorbents with complex organization requires knowledge of their structural features. A method of allowing for the effect of osmotic pressure on the polymer sorption capacity is proposed. The pair interaction parameters estimated in this study are compared with the published data.

Sorption and Diffusion of Water in Poly(vinylpyrrolidone)

The effect of molecular mass, thermal prehistory, physical state, and three-dimensional chemical crosslinked structure of a polymer on dissolution and diffusion in the PVP-water system has been studied. The kinetic dependences of sorption that correspond to the Fickian or pseudonormal type have been measured. In a certain concentration range, sorption is accompanied by transition of the system to the rubbery state. In the glassy state, the negative concentration dependence of the diffusion coefficient related to the nonequilibrium state of the polymer sorbent is observed. Sorption isotherms are described by S-shaped curves. It has been shown that the thermal prehistory of the polymer sorbent has the most pronounced effect on its sorption behavior. The effect of molecular mass is insignificant, while three-dimensional chemical crosslinks in PVP manifest themselves only in the region of the rubbery state. In accordance with the double sorption model, the experimental isotherms are represented as the superposition of two isotherms described by the Langmuir and Flory-Huggins equations. For the glassy state of the polymer sorbent, the degree of the nonequilibrium state has been estimated. With due regard for the excess free volume, the detailed thermodynamic analysis of isotherms has been performed; namely, the pair interaction parameters and the free energy of mixing have been calculated. The state of water in the polymer has been examined within the framework of hydrate contributions and clusterization theory.

Diffusion and phase behavior of a hydroxypropylcellulose-poly(ethylene glycol) system

The solubility and interdiffusion between hydroxypropylcellulose samples of various molecular masses (M w = 8 × 104, 14 × 104, 37 × 104, 85 × 104, and 115 × 104) and poly(ethylene glycol) (M w = 400 and 1500) in the range 18–210°C have been studied by optical interferometry and polarization microscopy methods. Oligomeric poly(ethylene glycols) have been considered as solvents for hydroxypropylcellulose. Phase diagrams have been constructed, and Flory-Huggins thermodynamic interaction parameters have been calculated. For the hydroxypropylcellulose-poly(ethylene glycol) 400 system, an LC and crystalline equilibria have been realized. An increase in the M w of hydroxypropylcellulose to 1500 leads to the appearance of a wide region of amorphous phase segregation with a UCST, whereas the liquidus line is conserved at high concentrations of hydroxypropylcellulose. Such a superposition of two kinds of phase equilibrium that is achieved only with a change in M w of the oligomeric solvent has been observed for the first time. For all the systems under examination, the kinetics of diffusion mixing has been estimated and the activation energies of the process have been calculated. The concentration dependences of diffusion coefficients demonstrate jumps in the mesomorphic-transition region.

The effect of aminoalkoxy and glycidoxyalkoxy silanes on adhesion characteristics of double and triple copolymers of ethylene

The effect of aminoalkoxy and glycidoxyalkoxy silanes on strength of a polyethylene-modified copolymer-metal (polyethylene terephthalate) adhesion joint was studied for double and triple acetate copolymers of ethylene. It was shown that such modification resulted in an essential increase in the deformation-strength and adhesion characteristics of adhesive joints.

Phase structure of silanol-modified ethylene-vinyl acetate copolymers

For (ethylene-vinyl acetate copolymer)-tetraethoxysilane and (ethylene-vinyl acetate copolymer)-polydimethylsiloxane systems, the solubility of components has been studied in a wide range of temperatures and compositions. Phase diagrams have been constructed, pair interaction parameters have been calculated, and diffusion coefficients and activation energies of diffusion have been estimated. The temperature and concentration ranges of a change in solubility related to chemical interactions between the components have been revealed, and the structure of the modified copolymers has been studied. On the basis of the kinetic data on the movement of isoconcentration planes in diffusion zones of component mixing, time intervals corresponding to the onset of the chemical reaction between the components have been determined and the apparent activation energies of the process have been computed. Complex-shaped binodal and boundary curves have been interpreted within the framework of the classical Flory-Huggins theory.

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.

Structure of binary mixtures of ethylene-vinylacetate copolymers

The method of differential scanning calorimetry was used to analyze the structure of binary mixtures of ethylene and vinylacetate copolymers with different contents of reagent monomers. The anomalous deviation of the degree of crystallinity from additivity in the system is found and a possible interpretation of this experimental fact is suggested.

Effect of structural heterogeneity of ethylene-vinylacetate copolymers modified by ethyl silicate on their stress-strain characteristics

Structural and morphological studies of ethylene-vinylacetate copolymers modified by tetraethoxysilane have been performed. It has been found that microheterogeneity of cevilens is caused by phase separation of oligomeric siloxane fragments. The observed effect of elastication in CEVA-ETS systems is due to the structural heterogeneity of the material.

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.

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.