A new procedure for the determination of molar mass distribution from sedimentation equilibrium runs in an analytical ultracentrifuge (AUC), 1. Measurements with interference optics

A new procedure for the determination of the number-, weight- and z-average molar masses M?_n, M?_w and M?_z and a model molar mass distribution W(M) has been developed from measurements of the sedimentation equilibrium. The method is based on the determination of the experimentally measured reduced concentration profile by extrapolation to zero concentration and direct calculation of the molar mass distribution W(M) by nonlinear regression of the integral equation according to the Simplex procedure. Results obtained in different solvents for the well characterized polystyrene NBS 706 with broad distribution are reasonable. Generally, it can be concluded that the suggested procedure is a suitable possibility for the determination of molar mass average values and the molar mass distribution of polymers if the latter is a log-normal, Schulz-Flory or Poisson distribution.