Absolute determination of molecular weights of standard polystyrenes by means of sedimentation‐diffusion measurements in toluene

Abstract

AbstractSedimentation coefficients, s0c, diffusion coefficients, Dc, and specific viscosities have been determined for eleven samples of commercial narrow‐molecular‐weight distribution polystyrenes Pressure Chemicals Co. and Waters Ass., 5 · 104 g · mol−1 < weight average molecular weight Mw < 2 · 106 g · mol−1 at different concentrations in toluene (25°C). From the Svedberg equation the values of the MsD averages have been calculated from the sedimentation and diffusion coefficients extrapolated to infinite dilution. The reproducibility of the measured values of s00, D0 and [η] was better than 3%. The parameters determined for the same samples in Prague and in Uppsala (using different instruments and different data evaluation techniques) were in good agreement (the maximum deviation 6%). The plots of log s00 vs. log D0 and log [η] vs. MsD are linear without any systematic deviations; all experimental hydrodynamic data are consistent within the interval of experimental error, i.e. ±3%. However, when plotted versus the nominal molecular weights the scatter is considerably increased. Furthermore, the calculated average molecular weights, MsD, differ in several instances from the nominal ones.