Ionic interaction behavior and facilitated olefin transport in poly(n‐vinyl pyrrolidone):Silver triflate electrolytes; Effect of molecular weight

Abstract

AbstractInteractions of cation/anion and cation/polymer in poly(N‐vinyl pyrrolidone) (PVP):silver triflate (AgCF3SO3) electrolytes with different weight‐average molecular weights (Mw's) of 1 × 106 (1 M), 3.6 × 105 (360 K), 4 × 104 (40 K), and 1 × 104 (10 K) have been studied with IR and Raman spectroscopies. According to the change of the CO peak, coordination of silver ions by CO in a low Mw (10 or 40 K) PVP matrix tend to be always thermodynamically favorable than high Mw (1 M or 360 K) PVP, demonstrating that the polymer matrix of low Mw dissolves silver salts more effectively. In addition, silver cations interact with both larger SO and smaller CF3 to form ion pairs, and the former interaction is stronger than the latter in a monomer or low Mw polymer matrix (40 K, 10 K), as demonstrated by theoretical ab initio calculation or experimental spectroscopy, respectively. However, CF3 interacts more favorably with silver cation than SO in high Mw (1 M and 360 K) PVP, which is ascribed to the steric effect of the bulky SO anion by highly entangled polymer chains. Despite the superior dissolving property of the low Mw polymer matrix, the membranes consisting of low Mw PVP and AgCF3SO3 exhibited poor separation performance for propylene/propane mixtures in comparison with those of high Mw, presumably because of the poor mechanical property for membrane formation in low Mw PVP. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1813–1820, 2002