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 (Tos) 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 T o for all the samples except the lowest P.. Further, C * s in this temperature range are proportional to P~- 05 , 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 R~ is observed in the T o 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 T o and PVA concentration dependences of u.v. transmission.
Посилання на статтю:
Gels of poly(vinyl alcohol) from dimethyl sulphoxide/water solutions / Masatoshi Ohkura, Toshiji Kanaya and Keisuke Kaji // Polymer. – 1992. – Vol 33. – P. 3686-3690.