The gelation process of aqueous solutions of a syndiotacticity-rich poly (vinyl alcohol), which was derived from vinyl trifluoroacetate, has been studied by measuring the zero- shear solution viscosity η
t0 as functions of the standing time t at a constant temperature, 30 or 50°C. After the solutions with polymer concentrations higher than about 1.0g/di were transferred from high temperature to the test temperature, the viscosity η
t0 increased with time
t until the gelation took place. The plot of log η
t0 versus
t is generally divided into three linear regions with different slopes,
i. e., the slow initial, the steep second, and the still steeper third regions. The second and third regions obey Avrami's equations with exponents, 1.7 and 3.6, respectively, suggesting that these regions correspond to the linear growth and three dimensional growth of crystallite in a heterogeneous nucleation system.
The linear dependence of log η
t0 on
t has been derived theoretically by using a linear association model of polymer chains. It has been conjectured that 7~8 mol% of polymer molecules participates in bimolecular association in the initial region and about 20 mol% in the second region.
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