Gels of poly(vinyl alcohol) from dimethyl sulphoxide/water solutions

Abstract Sol-gel diagrams of atactic poly(vinyl alcohol) (at-PVA) in a mixture of dimethyl sulphoxide and water (60/40 vol/vol) have been investigated. The crosslinking points of the gels are crystallites of PVA. Gelation of seven samples of at-PVA having degrees of polymerization (Pn) ranging from 186 to 20 200 was observed at quenching temperatures (TQs) between −60°C and 80°C. Gelation time, which is defined as time required for gelation, decreases with decreasing TQ. In a temperature range below ∼ −20°C, the gels are transparent and the critical gelation concentrations ( C∗ s ) are independent of TQ for all the samples except the lowest Pn. Further, C∗ s in this temperature range are proportional to P−0.5n, suggesting that C∗ is determined by the polymer chain overlap concentration. On the other hand, gels formed above −20°C are not transparent, and the degree of transparency decreases with increasing TQ. The lowest C∗ which is lower than the overlap concentration for polymer chains with radius of gryration Rg is observed in the TQ range of −20 to 40°C. This may be explained by the effect of liquid-liquid phase separation or spinodal decomposition, which is supported by TQ and PVA concentration dependences of u.v. transmission.