FT-raman studies on ionic interactions in π-complexes of poly(hexamethylenevinylene) with silver salts

Abstract

Remarkably high and stable separation performance for olefin/paraffin mixtures was previously reported by facilitated olefin transport through π-complex membranes consisting of silver ions dissolved in poly(hexamethylenevinylene) (PHMV). In this study, the π-complex formation of AgBF 4 , AgClO 4 and AgCF 3 SO 3 with PHMV and their ionic interactions were investigated. FT-Raman spectroscopy showed that the C=C stretching bands of PHMV shifted to a lower frequency upon incorporation of silver salt, but the degree of peak shift depended on the counteranions of salt due to different complexation strengths. The symmetric stretching modes of anions indicated the presence of only free ions up to [C=C]:[Ag]=1:1, demonstrating the unusually high solubility of silver salt in PHMV. Above the solubility limit, the ion pairs and higher-order ionic aggregates started to form. The coordination number of silver ion for C=C of PHMV was in the order AgBF 4 AgClO 4 AgCF 3 SO 3 , but became similar at [C=C]:[Ag]=1:1. The different coordination number was interpreted in terms of the different transient crosslinks of silver cations in the complex, which may be related to both the interaction strength of the polymer/silver ion and the bulkiness of the counteranion.

Olefin separation performances and coordination behaviors of facilitated transport membranes based on poly(styrene-b-isoprene-b-styrene)/silver salt complexes

“…Only a single band at 1030 cm -1 was observed up to 0.2 of silver mole fraction, attributable to the stretching band of free SO 3 -anion. 24,25 At higher silver concentrations, i.e. 0.25 and 0.33 of silver mole fraction, the main band slightly shifted to higher wavenumber at 1031 cm -1 , which seems to be still due to free SO 3 -anions.…”