Cation environment in polyether complexes based on poly (tetramethylene glycol) doped with zinc and cobalt chlorides

X-ray absorption spectroscopy [extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANTES)], differential scanning calorimetry, and Raman spectroscopy measurements were performed for a series of liquid polyether/salt systems prepared with poly(tetramethylene glycol) (PTMG) and the copolymer poly(tetramethylene glycol-co-ethylene glycol) as matrices and zinc and cobalt chlorides as dopants in the concentration range of n = 30-90, where n is the molar ratio of oxygen to metal cation. According to EXAFS, XANES, and Raman results, even in diluted solutions, these complexes exist mostly as undissociated ZnCl2 and CoCl2 species, presenting a weak cation-polymer interaction. EXAFS results indicate that for polymer/ZnCl2 systems, the nearest metal neighbors are only chlorine atoms. However, for polymer/CoCl2 samples, oxygen is also observed coordinating the metal. Raman spectra do not support any feature related specifically to the cation-polymer interaction. Nevertheless, for both salts the symmetric stretching vibrations are located in frequencies characteristic of salt in solution, which means that the polymer solvating action is effective. Differential scanning calorimetry data show an increase in the glass-transition temperature for all polymer/salt systems in relation to the pure polymer samples, a consequence of the increase in the macromolecular chain stiffening produced by the presence of the salt. This result corroborates the existence of polymer-salt interactions. (C) 2001 John Wiley & Sons, Inc.