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

Remarkably high and stable separation performance for olefin/paraffin mixtures was previously reported by facilitated olefin transport through pi-complex membranes consisting of silver ions dissolved in poly(hexamethylenevinylene) (PHMV). In this study, the pi-complex formation of AgBF4, AgClO4, and AgCF3SO3 with PHMV and their ionic interactions were investigated. FT-Raman spectroscopy showed that the C=C stretching hands of PHMV shifted to a lower frequency upon incorporation of silver salt, but the degree of peak shift depended oil the counter-anions of salt due to different complexation strengths. The symmetric stretching modes of anions indicated the presence of only free ions Lip 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 AgBF4 > AgClO4 > AgCF3SO3, 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.