GEL PERMEATION CHROMATOGRAPHY OF POLYMERS DEGRADING RANDOMLY IN THE COLUMN - THEORETICAL TREATMENT AND PRACTICAL ASPECTS

摘要

Gel permeation chromatography (GPC) separation accompanied with the random degradation of polymer in the column is modelled by a set of continuity equations. Numerical solution of the equations yields: (i) time evolution of the axial concentration profiles of all X-mers that visualize a course of the processes running in the column; and (ii) the number-distribution function of degrees of polymerization (DP) of each polymer fraction passing through the detector (i.e., of each GPC-slice). These data are evaluated by the exact approach way and by conventional methods based on DP values taken from the calibration curve or measured by a light-scattering (LS) detector. Thus obtained DP averages are compared with each other, with those predicted by the theory of polymer random degradation and with those of the non-degraded original polymer. The procedure of determination of the degradation rate constant and original values of DP averages of the degrading polymer with a help of the kinetic equation of random degradation has been also simulated and the following conclusions have been reached: the degradation rate constant is available from GPC measurements performed with the use of both a single concentration detector and its combination with the LS detector. In contrast, the values of DP averages of original non-degraded polymer are not available except for the original weight-average DP provided that values of weight-average DP of degraded polymer are measured with an LS detector. Extrapolation to zero degradation time of the DP values obtained by the calibration curve method yields overestimated DP values of non-degraded polymer. (C) 1997 Elsevier Science B.V