Study of Cryostructuring of Polymer System. 65. Features of Changes in the Physicochemical Properties of Poly(vinyl alcohol) Cryogels Caused by the Action of Aqueous Solutions of Amino Acids of General Formula H2N–(CH2)n–COOH

Abstract

Macroporous cryogels of poly(vinyl alcohol) (PVA) have been prepared by the cryogenic processing (freezing at –20°C for 12 h followed by defrosting through heating at a rate of 0.03°C/min) of aqueous PVA solutions with a polymer concentration of 100 g/L. The character of changes in the physicochemical parameters of the cryogels has been studied after equilibrating their samples with aqueous solutions of amino acids of general formula H₂N–(CH₂)_n–COOH (n = 1–5). It has been shown that these amino acids, glycine (n = 1) and ε-aminocaproic acid (n = 5) to the highest and lowest extent, respectively, impose a kosmotropic action on the properties of the PVA cryogels causing a decrease in their volume, a significant increase in the compression elasticity modulus, and a rise in the fusion temperature of the samples. Nevertheless, H₂N–(CH₂)_n–COOH amino acids are released from the cryogels saturated with amino acid solutions into an external aqueous environment with no significant diffusion hindrances. After cryogels loaded with amino acids are exhaustively rinsed with pure water, their physicochemical parameters do not return completely to the values observed for the samples before their treatment with solutions of such amino acids due to the formation of additional H-bonded nodes of a three-dimensional network, with their formation being promoted by kosmotropic amino acids in the bulk of the already formed cryogels.