Gels of some polymeric polyols cross-linked by berate can be liquefied by certain low molecular weight polyols. As the gels respond with some molecular selectivity, we view them as model smart materials. In an effort to gain a quantitative understanding of such chemically responsive polymer systems, we have studied the gelation of atactic poly(vinyl alcohol) (PVA) by berate and have at the same time determined the equilibrium concentration of berate in free solution in the presence of various concentrations of polymer. The standard approach to the determination of the distribution of berate among its various forms-free berate, free boric acid, berate bound to a diol (monodiol), and borate bound to a pair of diols (didiol)-is to use the relevant chemical equilibria and the diol concentration dependence of the berate distribution. This is not appropriate for polymer systems. We have developed a model that uses simple geometrical arguments to define the volume fraction of a polymer solution in which two chains are close enough to be cross-linked. This volume is used with the berate chemical equilibria to define how many berate cross-links there are. From this model, which is generally applicable to chemically reversible gels, experimentally observed gel points and equilibrium concentrations of free berate are predicted when using reasonable input parameters. Furthermore, the model also predicts the mean chain length between cross-links.