Theory of interaction of polymer and small molecules which can aggregate in solution

The theory of interaction of small molecules with polymers is extended to the case where the small molecules can aggregate in solution to form dimers, trimers, etc., and where the aggregates can also interact with the polymer. The secular equation is found to be identical in form with that obtained for the binding of nonaggregating monomer to the polymer. Thus, all formulas derived for the latter case apply to the present one also, except that, now the concentration of the free monomer is the relevant factor. It is shown how the experimental data can be analyzed by using information on the molal activity coefficients of the small molecules. As an illustration these formulas are applied to data on the interaction of purines and nucleosides with poly(uridylic acid) in concentrated solutions.