Gelation kinetics in aqueous solutions of syndiotactic‐rich poly(vinyl alcohol)

Aqueous solutions of Syndiotactic‐rich poly(vinyl alcohol) (PVA) form thermally reversible gels. The volume of the solution decreases with gelling time on standing at isothermal condition. Assuming that the gelation is due to the crystallization of PVA, the kinetics of isothermal crystallization from 5 wt.‐% aqueous solutions of PVAs having 64,3 mol‐% syndiotactic diads was investigated as a function of temperature (45–90°C), using dilatometry. The maximum in the overall rate of crystallization appeared at 60°C, regardless of the degree of polymerization of PVA. Since the values of n in the Avrami equation vary from about 1 to 2, it was apparent that the crystallization from aqueous solution of the polymer proceeded in the fashion of one‐dimensional growth and heterogeneous, diffusion controlled nucleation. The phase diagram revealed that the syneresis of the gel was caused by the crystalline phase separation which supports the gelation accompanying crystallization.