Solid polymers doped with rare earth metal salts. I. Complex formation and morphology in the neodymium chloride–poly(ethylene oxide) system

The complex formation and morphology of the NdCl₃?PEO system have been investigated. Peak shifts, peak broadening, and the appearance of new peaks in the 800–1200 cm^?1 range of the infrared (IR) spectra, by comparison with what is observed with pure PEO, unequivocally demonstrates complex formation. Although the NdCl₃?PEO complex is found to be highly hygroscopic, residual moisture can be removed reversibly, thereby permitting the role of water in affecting the morphology of the solid film to be examined. As elucidated with infrared, differential scanning calorimetry, thermogravimetric analysis, and hot-stage polarized optical microscopy, under anhydrous conditions the resultant complex is amorphous at an EO/NdCl₃ ratio approximately less than ca. 8; but above this critical value the PEO in excess of the stoichiometric ratio required for complexation tends to form a separate crystalline phase. Furthermore, water was found to compete with the ethylene oxide unit for complexation with Nd³⁺, resulting in phase-separated PEO with a tendency toward crystallinity. The glass transition temperature of the complex is found to increase sigmoidally with the NdCl₃ content, an observation further substantiating complexation between NdCl₃ and PEO.