Separating impurities produced by the cyclization of PEG

Abstract

Poly(ethylene glycol) (PEG) is biocompatible, which makes it useful in biomedical materials for applications in tissue engineering, controlled drug delivery, and thermoresponsive materials. Our group has developed the synthesis of cyclic and linear PEG based monomers to study how architecture affects thermoresponsive properties. However, the Williamson etherification reaction (second step) to synthesize the cyclic unimer by intramolecular cyclization also has unavoidable intermolecular cyclization, thus producing dimer and higher-order impurities. The purification method developed to isolate the desired cyclic unimer from the impurities utilizes Sephadex LH-20, a size exclusion chromatography technique. Gel permeation chromatography (GPC) was not only used to determine which fractions contained isolated unimers, the results also revealed that the ultraviolet (UV) detector is highly sensitive to the dimers and is therefore essential in confirming successful isolation. The repeatability, reproducibility, and efficacy of one column used over four samples was analyzed using the consistency of sample recovered versus the fraction elution volume. This comparison demonstrated that this technique was repeatable and reproducible over the four samples, but the efficacy of separation suffered after the third sample.