Chain Length Dependent Polymer End−End Reaction Rate Constants in the Reaction of Polystyryllithium with a Styrene-Terminated Fluorescent-Labeled Polystyrene

Gel permeation chromatography with fluorescence detection has been employed to measure polymer−polymer chain end reaction rate constants. In this study, polystyryllithium (PSLi 1 ) of varying chain lengths (degree of polymerization N varying between ∼31 and 246) has been reacted with a styrene-terminated polystyrene 4 (degree of polymerization M ∼ 22) which is labeled with the fluorescence probe pyrene. This study, which was performed in a good solvent (benzene) at the dilute/semidilute threshold and extending into the semidilute regime, reveals a concentration dependence on 1 of this reaction that is close to first order (0.9 ± 0.1). Interestingly, the reaction rate constant at fixed concentration of polystyryllithium ( c = 0.3 g/mL) increases with increasing chain length, from 3.6 M -1 min -1 at N = 31 to 10.3 M -1 min -1 at N = 246. Possible reasons for this unexpected rate increase with chain length are discussed in the context of aggregation and supramolecular effects.