Degradation of High Molecular Weight Polystyrenes During the SEC Separation Process, as Demonstrated by SEC Coupled with Lalls and by Static Light Scattering

Abstract

In order to investigate the phenomenon of polymer degradation during the SEC separation process, we compared the weight-average molecular weights of a series of polystyrene (PS) samples with M_w going from 2.3×10³ to 1.84×10⁷, which were determined by static light scattering (LS) and by SEC-LALLS using various crosslinked PS gels.

For all the gels considered, there was a good agreement between LS and SEC-LALLS values for M_w up to 2×10⁶. For higher M_w, the values given by SEC-LALLS were lower than those given by LS; the decrease in M_w was different in various SEC columns. Since the same chromatographic equipment was used for all the SEC-LALLS measurements, we presumed that the decrease in M_w reflected the degree of shear degradation of PS molecules during their elution through the SEC columns. It depended on the origins of gels, the size of gel particles, the porosity of frits at column ends, the eluent flow rate, the usage of a pre-column filter, and of the third detector, a capillary viscometer.