Study of the Degradation of High Molecular Weight Polystyrene in the Course of Size Exclusion Chromatography (SEC)

Abstract

The possibility of degradation of large macromolecules in their motion through a porous medium in the course of SEC decreases considerably the range of application of this highly productive and highly selective analytical method for the determination of the MWD of polymers. In fact, the MWD determined by SEC with the existence of degradation is mainly the distribution according to degradation fragments and does not reflect the initial molecular characteristics of the polymer.

The dependence of the degree of degradation of maccromolecules on the main parameters of the chromatographic experiment: the rate of the eluent flow, the size and shape of sorbent particles and the size of their pores was studied in detail. A non-monotonic change in the degree of degradation with increasing flow rate of the eluent was detected.

It is shown that the degree of degradation increases with decreasing particle size and the size of their pores. A new concept of the degradation of high polymers in SEC is formulated. It is related mainly not to the existence of local rate gradients in the interparticle volume but, rather, to the entire combination of hydrodynamic and adsorption effects accompanying the process of interaction between the macromolecules and the surface of sorbeiit particles. Practical recomendations are given for carrying out SEC, including that of super-high molecular weight samples under “non-degrada- tive” condritions.