Structural Study on Water-induced Phase Transitions of Poly(ethylene imine) as Viewed from the Simultaneous Measurements of Wide-Angle X-ray Diffractions and DSC Thermograms

Thermal behavior of poly(ethylene imine) PEI] has been studied using simultaneous WAXD/DSC measurement system. PEI exhibits water-induced and thermally-induced phase transitions among four kinds of crystalline hydrates: anhydrate (EI/water = 1/0), hemihydrate (1/0.5), sesquihydrate (1/1.5), and dihydrate (1/2). The chain conformation changes from a double helix in the anhydrate to a planar zigzag form in the three hydrates. The anhydrate melts at 60 °C while the hydrates melt differently in the temperature region of 70–110 °C. By means of the simultaneous WAXD/DSC measurements, complex DSC thermograms of PEI hydrates were characterized on the basis of X-ray diffractions obtained concurrently.