Polystyrene Cyclization Using Pyrene Excimer Formation. Effect of Geminate Pairs in Good Solvents

The cyclization of polystyrene chains ( M̄ n = 2600, M̄ w / M̄ n = 1.07; M̄ n = 4500, M̄ w / M̄ n = 1.08), both-ends labeled with 1-pyrenyl groups, was studied in the range of temperatures 25−90 °C, in two good solvents (toluene and 1,4-dioxane) and one poor solvent (methylcyclohexane). In methylcyclohexane a two-state Birks kinetics is followed, but in good solvents at high temperatures the contribution of geminate pairs recombination must be considered. Values of the standard enthalpies, Δ H °, and entropies, Δ S °, for excimer formation were determined from the van't Hoff plots. The Δ S ° values are solvent and chain length dependent, while the Δ H ° values are, within the experimental error, chain length independent.