GELS OF POLY(VINYL ALCOHOL) FROM DIMETHYL-SULFOXIDE WATER SOLUTIONS

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 (P(n)) ranging from 186 to 20 200 was observed at quenching temperatures (T(Q)s) between -60-degrees-C and 80-degrees-C. Gelation time, which is defined as time required for gelation, decreases with decreasing T(Q). In a temperature range below approximately -20-degrees-C, the gels are transparent and the critical gelation concentrations (C*s) are independent of T(Q) for all the samples except the lowest P(n). Further, C*s in this temperature range are proportional to P(n)-0.5, suggesting that C* is determined by the polymer chain overlap concentration. On the other hand, gels formed above -20-degrees-C are not transparent, and the degree of transparency decreases with increasing T(Q). The lowest C* which is lower than the overlap concentration for polymer chains with radius of gryration R(g) is observed in the T(Q) range of -20 to 40-degrees-C. This may be explained by the effect of liquid-liquid phase separation or spinodal decomposition, which is supported by T(Q) and PVA concentration dependences of u.v. transmission.