CHARACTERIZATION OF LOW-MOLAR-MASS POLYMERS BY GRADIENT POLYMER ELUTION CHROMATOGRAPHY .1. PRACTICAL PARAMETERS AND APPLICATIONS OF THE ANALYSIS OF POLYESTER RESINS UNDER REVERSED PHASE CONDITIONS

摘要

The application of gradient elution techniques such as gradient polymer elution chromatography (GPEC) for the characterization of low-molar-mass polymers has been known for a long time. Until now, however, practical applications have been lacking. The objective of this study was to find out to what extent GPEC can be useful to provide information on the (micro)structure of these materials. The influence of some practical parameters in GPEC under reversed-phase conditions with tetrahydrofuran 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 separation at the cost of a much longer analysis time. Increasing the column length or temperature only significantly improve the separation in the low-molar-mass part of the chromatogram. A sample load of up to 1 mg does not influence the separation. This indicates that separation is probably dominated by sorption (adsorption and/or partitioning) rather than solubility effects. Injection volumes exceeding 10 mu l give rise to additional 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 calculate average molar masses for one polyester. The M(w) thus calculated, agreed well with absolute methods. The oligomer distribution obtained using GPEC was in excellent agreement with the theoretical 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 chemical composition distribution could be obtained.