Poly(Vinyl Alcohol) Cryogels Formed from Polymer Solutions in Dimethyl Sulfoxide with Tetramethoxysilane Additives

Organic–inorganic hybrid cryogels of poly(vinyl alcohol) (PVA) containing silica inclusions (SiO2) were obtained and studied. Such inclusions were formed in the course of hydrolytic polycondensation (sol-gel process) of tetramethoxysilane (TMOS) introduced into concentrated polymer solutions in dimethyl sulfoxide (DMSO). PVA concentration in these solutions was 60, 80 or 100 g/L; while the concentration of TMOS was varied in a range of 0.15–0.61 mol/L. The polymer solutions were subjected to the cryogenic treatment at temperatures by 40 °С lower than DMSO crystallization temperature (+18.4°C). The frozen samples were thawed out at a heating rate of 0.03°/min. It is shown that moderate freezing at −21.6 °C, then frozen storage and subsequent thawing of the initial reaction mixture PVA/DMSO/TMOS/acid catalyst resulted in the formation of strong macroporous PVA/SiO2 cryogels. Such cryogel materials are hybrid systems, because the gel-forming polymer and the silica containing moieties belong to the content of the gel phase. The basis of this intermolecular interaction is hydrogen bonding between OH groups of the adjacent chains. This leads to the formation of modified microcrystallinity zones that perform as the nodes of the three-dimensional network of cryogels. The effects of significant increase in their rigidity and heat-resistance with increasing PVA and TMOS concentration in the initial feed were also observed. It was shown that the success of the synthesis of transparent elastic and heat-resistant PVA/SiO2 cryogels depends on the choice of the optimal ratio between the precursors and the combined effect of the liquid (methanol and water) and silicon-containing components on the formation of multiple hydrogen bonds and microcrystallites.