SIZE-EXCLUSION CHROMATOGRAPHY WITH 2-ANGLE LASER LIGHT-SCATTERING (SEC-TALLS) OF HIGH-MOLECULAR-WEIGHT AND BRANCHED POLYMERS

The accuracy and precision of results obtained from light-scattering detection at two angles (TALLS) for size-exclusion chromatography (SEC) are examined for linear narrow molecular weight distribution polystyrenes between 1,290,000 and 20,000,000 MW and for branched polyesters. The ratio of light-scattering intensities at 15 degrees and 90 degrees is used to calculate weight-average molecular weight, (M) over bar(w), and an average root-mean-square radius, (r) over bar(gu), equivalent to the z-average radius. A shape for the polymer molecule is assumed and an analytical relationship for the particle-scattering function is required. It is shown that analysis of the data using the particle-scattering function for a random coil is valid for both high molecular weight, linear polystyrenes and long-chain branched polyesters. The radius, (r) over bar(gu) is determined with high precision by using the ratio of light-scattering signals, which is insensitive to errors in sample concentration and changes in the eluent flow rate. The correct average radius for the whole polymer is obtained despite using low-efficiency, large-particle diameter SEC columns; however, axial dispersion significantly affects molecular weights and radii calculated at each retention volume that can limit the utility of plots used to deduce polymer conformation. (C) 1995 John Wiley and Sons, Inc.