GELATION RATES OF POLY(VINYL ALCOHOL) SOLUTION

Apparent gelation rates t(gel)-1, defined as the reciprocal of the gelation time. are measured for poly(vinyl alcohol) solutions as functions of polymer concentration, C(p), and quenching temperature, T(Q). Here the measurements are limited to the case of homogeneous gelation where T(Q) is below 0-degrees-C. The critical gelation concentration, C(t=infinity)*, extrapolated to t(gel)-1 = 0 is independent of T(Q), and is identical to the polymer chain overlap concentration, C(Rg)*. In order to represent the degree of polymer chain overlap a reduced concentration, phi = (C(p)-C(Rg)*)/C(Rg)*, is introduced. An experimental relation, t(gel)-1 = A(T(Q)) phi2, is obtained where A(T(Q)) is the temperature factor. The phi dependence of the equation can be explained using the chain overlap concept for gelation and random bond percolation theory, and the temperature factor A(T(Q)) is analysed by the crystal nucleation theory.