Direct determination of molecular weight distributions of polystyrene in cyclohexane with photon correlation spectroscopy

Abstract

A recently proposed method for analyzing polydispersity with photon correlation spectroscopy is verified experimentally by directly estimating the molecular weight distributions (MWD’s) of two well characterized National Bureau of Standards (NBS) polystyrene samples in cyclohexane at 35.0 °C. The MWD’s were reproducible and in good agreement with the NBS molecular weight averages. The method finds the smoothest nonnegative MWD that is consistent with the data without requiring initial estimates or subjective judgements. It is shown to work at dust levels where the method of cumulants fails. Minimum necessary precautions against dust and other sources of error are discussed.