Solution cation-binding properties of segmented polyethylene oxide- a ¹³C NMR spectroscopic study

Abstract

Two segmented polyethylene oxides, SPEO-3 and SPEO-4, were prepared using a novel transetherification methodology. Their structures were confirmed by ¹H and ¹³C NMR spectroscopy. The complexation of these SPEO's with alkali-metal ions in solution was investigated by ¹³C NMR spectroscopy. The mole-fraction method was used to determine the complexation ratio of SPEO with LiClO₄ at 25 °C, which showed that these formed 1:1 (polymer repeat unit/salt) complexes. The association constant, K, for the complex formation was calculated from the variation of the chemical shift values with salt concentration, using a standard nonlinear least-square fitting procedure. The maximum change in chemical shift (Δδ) and the K values suggest that both SPEO-3 and SPEO-4 formed stronger complexes with lithium salts than with sodium salts. Unexpectedly, the K values were found to be different, when the variation of δ of different carbons was used in the fitting procedure. This suggests that several possible complexed species may be in equilibrium with the uncomplexed one. Structurally similar model compounds were also prepared and their complexation studies indicated that all of them also formed 1:1 complexes with Li salts. Interestingly, it was observed that the polymers gave higher K values suggesting the formation of more stable complexes in polymers when compared to the model analogues.