Thermosensitive gels incorporating cyclic monoazatetrathioether units for the selective extraction of class b metal ions

Abstract

A cyclic monoaza–tetrathia-crown ether, 1-aza-4,7,11,14-tetrathiacyclohexadecane (ATCH) unit have been introduced into the temperature responsive polymer, poly-N-iso-propyl-acryl-amide. The synthesized copolymers were examined for the selective extraction of soft metal ions such as silver(I) and copper(I) ions. The ratio between N-isopropylacrylamide group and cyclic monoazatetrathioether group in the copolymer was clarified by the determination of sulfur atoms in aqueous solution of the copolymer by means of ICP-AES measurements of the sulfur atoms. It varied in the range of 55:1 to 269:1. Each lower critical solution temperature of the copolymer solution was determined spectrophotometrically by the relative absorbance change at 750 nm via temperature of the copolymer solution. Metal ion extraction using the copolymer with an appropriate counter anion such as picrate, nitrate or perchlorate ion was examined. Soft metal ions such as silver(I) and copper(I) ion were extracted selectively into the solid polymer phase. Extraction behaviors of silver(I) and copper(I) ions with the copolymer incorporating cyclic mono-aza-tetra-thio-ethers have been compared with the copolymer incorporating the acyclic analogues 9-aza-3,6,12,15-tetrathiaheptadecane (ATH). The extraction behavior of silver(I) ion with the copolymer of cyclic ATCH was different from that with the copolymer of acyclic ATH, because of the steric effect of cyclic monoazatetrathioether part.