Water State Analysis in Thermo Reversible Hydrogels

Abstract

Polyethylene Glycol (PEG) is considered to be environmentally and biologically friendly materials, and has been applied to industrial or biological use as a highly hydrophilic and viscous polymer. PEG-water systems in various molar ratios of ethylene oxide (constitutional repeating unit of PEG) to H₂O were investigated by DSC, NIR (Near infrared spectroscopy) and ¹⁷O NMR, in order to investigate the behavior of water molecules in PEG hydrogel. The results of DSC show good agreement with those of NIR, NMR measurements. In this study, we focused on the PEG - methylcellulose (MC) - water system at the water-rich region. The water state or the dynamic mechanical property was investigated. PEG {PEG 1500, 6000, molar fraction of ethilenoxide (EOX): 0.01 or 0.07} and MC (MC 50cP, 400cP, molar fraction of MC : 1.0 × 10⁻³) were used in this study. The PEG-MC-water system forms a thermo reversible gel in the heating process. We found that the memory of the gel state was kept for 3 days after gelling at room temperature. The period of keeping the memory of the gel state after gelling agreed with the strength of PEG-water interaction. It was found that the interaction was detectable by DSC.