Chemical networks of poly(vinyl alcohol)-Si hybrid films and the thermodynamics of their interaction with water

Organic-inorganic hybrid polymer films are prepared through the sol-gel method via the hydrolytic condensation of tetraethoxysilane in a 4% aqueous solution of poly(vinyl alcohol). The films are polymer networks containing O-Si-O bonds between chains formed via the interaction of OH groups of alcohol and Si-OH groups of the products of hydrolysis of tetraethoxysilane. The films contain 10.8–26.2 wt % Si in the polymer matrix. Isotherms of water-vapor sorption by the films are determined and used to calculate the molecular mass of polymer-chain fragments between crosslink-junction points in terms of the Flory-Rehner theory. For hybrid polymer networks, the products of sol-gel synthesis, this calculation is performed for the first time. The molecular mass of chain fragments between crosslink-junction points decreases from 9000 to 180 with an increase in the content of Si in the films. Poly(vinyl alcohol)-Si hybrid films are active during the separation of components of organic-aqueous media (a solution of tetrahydrofuran in water). The selectivity of the films increases as the molecular mass of chain fragments between crosslink-junction points decreases, that is, as the density of the chemical network increases.