Chain Stoppers in Reversible Supramolecular Polymer Solutions Studied by Static and Dynamic Light Scattering and Osmometry

Abstract

The effect of the addition of chain stoppers to solutions of hydrogen-bonded reversible supramolecular polymers was studied by vapor pressure osmometry and static and dynamic light scattering. Vapor pressure osmometry showed that within the range of concentrations studied the average degree of polymerization is independent of the overall monomer concentration and roughly inversely proportional to the mole fraction of chain stoppers, in agreement with theoretical predictions. The correlation length as measured by static light scattering has a maximum at the overlap concentration in solutions without chain stoppers. In the presence of a fixed fraction of chain stoppers, the results coincide with those without chain stoppers at low and high concentrations, but there is a plateau in the correlation length at intermediate concentrations. From the data, information about the association constant and the persistence length of the chains is obtained. The effectiveness of the chain stopper is discussed, and the results from osmometry and static light scattering are compared. Dynamic light scattering was used to measure the time autocorrelation function. From the characteristic decay time, the hydrodynamic correlation length was calculated. For solutions above the overlap concentration, the distribution of decay times showed a second peak at longer times. It is not yet fully understood what the mechanism behind this slow mode is.