Interaction between poly(ethylene glycol) and water as studied by differential scanning calorimetry

The interaction between poly(ethylene glycol) (PEG) and water was studied b y differential scanning calorimetry (DSC). The DSC curves of PEG-water syst ems were classified into three groups according to the difference in molecu lar weight. The melting peaks of eutectic mixture appeared for PEG with mol ecular weight higher than 1000. The eutectic point temperature shifted to h igher temperatures and the eutectic point composition shifted to lower conc entrations of PEG with increasing molecular weight. The maximum hydration n umber per ethylene glycol (EG) unit was estimated as 1.6, 2.4, and 3.3 for samples with molecular weights 400, 1540, and 70,000, respectively. No ther mal change was found in PEG1540-water system for a narrow weight fraction r ange of 0.585-0.605 for overall measuring temperatures due to perfect super cooling. The glass transition temperature shifted to higher temperatures wi th increasing molecular weight of PEG. A modified Flory-Huggins equation wa s used to fit curves for experimental liquidus data in phase diagrams. (C) 2001 John Wiley & Sons, Inc.