Cvclization of polystyrene chains in the crossover region between theta and good solvents: Cyclization dynamics of polymers 12

The rate constants and the equilibrium constants for end-to-end cyclization have been determined in seven solvents for a polystyrene chain of M_n - 2900 and narrow molecular weight distribution. These values were obtained by measuring the kinetics of intramolecular excimer formation between pyrene groups attached to the chain ends. Values were plotted versus the Hildebrand solubility parameter h: It was found that not only did the rate of cyclization decrease in good solvents, but that the rate of ring opening was substantially faster in good solvents than in poor solvents. Consequently, the cyclization equilibrium constant is far more sensitive to the quality of the solvent than is the mean-squared radius of gyration. The results are interpreted in terms of excluding volume effects on the end-to-end distance distribution function of the polymer.