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

Gel permeation chromatography (GPC) separation accompanied with the ra ndom degradation of polymer in the column is modelled by a set of cont inuity equations. Numerical solution of the equations yields: (i) time evolution of the axial concentration profiles of all X-mers that visu alize a course of the processes running in the column; and (ii) the nu mber-distribution function of degrees of polymerization (DP) of each p olymer fraction passing through the detector (i.e., of each GPC-slice) . These data are evaluated by the exact approach way and by convention al methods based on DP values taken from the calibration curve or meas ured by a light-scattering (LS) detector. Thus obtained DP averages ar e compared with each other, with those predicted by the theory of poly mer random degradation and with those of the non-degraded original pol ymer. The procedure of determination of the degradation rate constant and original values of DP averages of the degrading polymer with a hel p of the kinetic equation of random degradation has been also simulate d and the following conclusions have been reached: the degradation rat e constant is available from GPC measurements performed with the use o f both a single concentration detector and its combination with the LS detector. In contrast, the values of DP averages of original non-degr aded polymer are not available except for the original weight-average DP provided that values of weight-average DP of degraded polymer are m easured with an LS detector. Extrapolation to zero degradation time of the DP values obtained by the calibration curve method yields overest imated DP values of non-degraded polymer. (C) 1997 Elsevier Science B. V.