Characterization of low-molar-mass polymers by gradient polymer elution chromatography, I: Practical parameters and applications of the analysis of polyester resins under reversed phase conditions

The influence of some practical parameters in gradient polymer elution chromatog. (GPEC) under reversed-phase conditions with THF and water as the solvent-non-solvent combination, was investigated using a co-polyester resin. A gradient steepness less than 1%/min hardly improves the sepn. at the cost of a much longer anal. time. Increasing the column length or temp. only significantly improve the sepn. in the low-molar-mass part of the chromatogram. A sample load of up to 1 mg does not influence the sepn. This indicates that sepn. is probably dominated by sorption (adsorption and/or partitioning) rather than soly. effects. Injection vols. exceeding 10 ml give rise to addnl. peak broadening due to a sample solvent effect. For different polyesters, an almost linear dependence was found between the reciprocal square root of the molar mass and the percentage of solvent at the point of elution of an oligomer. This dependence was used to calc. av. molar masses for one polyester. The Mw thus calcd., agreed well with abs. methods. The oligomer distribution obtained using GPEC was in excellent agreement with the theor. distribution, thus demonstrating the feasibility of GPEC for providing information on reaction kinetics. By comparison of GPEC results for two co-polyester resins, evidence for differences in chem. compn. distribution could be obtained