DEGRADATION OF HIGH-MOLECULAR-WEIGHT POLYSTYRENES DURING THE SEC SEPARATION PROCESS, AS DEMONSTRATED BY SEC COUPLED WITH LALLS AND BY STATIC LIGHT-SCATTERING

In order to investigate the phenomenon of polymer degradation during t he SEC separation process, we compared the weight-average molecular we ights of a series of polystyrene (PS) samples with M-w going from 2.3x 10(3) to 1.84x10(7), which were determined by static light scattering (LS) and by SEC-LALLS using various crosslinked PS gels. For all the g els considered, there was a good agreement between LS and SEC-LALLS va lues for M-w up to 2x10(6). For higher M-w, the values given by SEC-LA LLS were lower than those given by LS; the decrease in M-w was differe nt in various SEC columns. Since the same chromatographic equipment wa s used for all the SEC-LALLS measurements, we presumed that the decrea se in M-w reflected the degree of shear degradation of PS molecules du ring their elution through the SEC columns. It depended on the origins of gels, the size of gel particles, the porosity of frits at column e nds, the eluent flow rate, the usage of a pre-column filter, and of th e third detector, a capillary viscometer.