Determination of Functionality and Molar Mass Distribution of Aliphatic Polyesters by Orthogonal Liquid Chromatography. I. Off-Line Investigation of Poly(1,6-Hexanediol Adipates)

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Abstract
During polycondensation of polyesters products are formed distributed in molar mass and functionality (end groups). Especially in polyurethane chemistry the knowledge of the distribution of terminal groups is necessary for correlating material properties containing different species in raw materials. The characterization of polyesters by “Liquid Adsorption Chromatography at Critical Conditions” (LACCC) is a new powerful tool for kinetics and modelling. Separation of polyesters according to their terminal groups independently of their molar mass is feasible at the critical conditions determined by the chromatographic system silica/acetone/hexane. Owing to side reactions, the number of combinations of COOH- and OH terminal groups identified was higher than expected. Cyclic species, hexanediol ether structures and alkyl-terminated homologues were identified. Model substances for all structures were synthesized. For orthogonal separation LACCC was combined off-line with SEC. With the help of preparative separation enough material was obtained to identify the species by spectroscopic methods (NMR, MALDI-TOF-MS) and to calibrate both the detector response and SEC. Finally, an algorithm is proposed for the characterization of end-group distributed reactive polymers by orthogonal liquid chromatographic methods.