S. V. Rogozhin

Study of cryostructurization of polymer systems VII. Structure formation under freezing of poly(vinyl alcohol) aqueous solutions

Rheological properties of the cryogels produced by freezing of concentrated aqueous solutions of poly(vinyl alcohol) have been studied. These properties were shown to depend on the polymer concentration in the initial solution, on PVA molecular weight, cryostructurization duration and temperature. Electron microscopy demonstrates the heterogeneous porous structure of these cryogels and the dependence of the observed pattern on the conditions of formation of the studied objects.

On the possibility of mechanodestruction of poly(vinyl alcohol) molecules under moderate freezing of its concentrated water solutions

SummaryThe freezing of the concentrated PVA water solutions results in obtaining (after thawing) hydrogels of non-covalent nature. In the course of a single freezing-thawing cycle there is no any noticeable destruction or covalent cross-linking of PVA macromolecules.

Study of cryostructurization of polymer systems: II. The influence of freezing of a reacting mass on the properties of products in the preparation of covalently cross-linked gels

The influence of freezing of a reaction mass on the properties of the resulting covalently cross-linked gels is exemplified by a system composed of a solution of chitosan in aqueous acetic acid and glutaric dialdehyde serving as a cross-linking agent. The freezing is shown to lead to a noticeable decrease of critical concentration of gelation as compared with the reactions of polymeric chain cross-linking in ordinary conditions. Consideration is given to some properties of three-dimensional networks obtained by cryostructurization.

Use of PVA-cryogel entrappedCitrobacter intermedius cells for continuous production of 3-fluoro-L-tyrosine

SummaryThe cells ofCitrobacter intermedius (containing L-tyrosine phenol lyase which catalyses the synthesis of 3-fluoro-L-tyrosine fromo-fluorophenol, pyruvate and ammonia) were entrapped into 10% poly(vinyl alcohol) cryogel beads. Cryogenic immobilization resulted in a moderate increase of the synthetic activity of the cells. During continuous operation for one month in a packed bed column reactor the productivity of the immobilized biocatalyst decreased by 30%.

Study of cryostructurization of polymer systems. V: Electron microscopic studies of cross-linked polyacrylamide cryogels

Light microscopy, scanning and transmission electron microscopy techniques were used to carry out investigations of cross-linked polyacrylamide cryogels prepared by freezing aqueous or formamide solutions of acrylamide and N,N′-methylene-bisacrylamide in the presence of a radical polymerization initiator. The application of different techniques for the preparation of gels to be studied with electron microscopes allowed a conclusion to be drawn on the reality of the porous structure of cryogels and on the macro- and microheterogeneity of their structure.