Isolation of cyclic penta(ethylene oxide) from mixtures with its linear analog by combining selective intercalation into graphite oxide and solvent approaches

Abstract

Cyclic oligomers of poly(ethylene oxide)s intercalate slower into graphite oxide (GO) than their linear analogs from the melt. In present study these kinetic differences are exploited to isolate 15-crown-5 (15C5) from mixtures with linear penta(ethylene glycol) (5EG) by using two approaches: a) melt intercalation and solvent extraction and b) intercalation from solution and filtration. In both cases we found that fractions highly enriched in the cyclic component are obtained by using an appropriate selection of the solvent. Solvents that do not penetrate the interlayer space of GO (such as CCl4 and toluene) lead to an increase of the cyclic fraction from 50 wt% in the initial mixture to values as high as 99 wt%. On the contrary, solvents that penetrate the interlayer space of GO produce fractions with low content of 15C5. The ability of non-penetrating solvents to achieve an effective isolation of 15C5 demonstrates that separation is driven by a faster intercalation of 5EG into unswollen GO, without solvent assistance, and the permanence of 15C5 in solution. These results are discussed in the light of data collected by X-ray diffraction, differential scanning calorimetry and gel permeation chromatography. This study provides substantial evidence of a very promising separation method for a topological purification of cyclic poly(ethylene oxide)s with GO.