Functional oligo(vinyl acetate) bearing bipyridine moieties by RAFT polymerization and extraction of metal ions in supercritical carbon dioxide

Abstract

A novel method is developed to functionalize the oligo(vinyl acetate) (OVAc) via a bipyridine (bpy) moiety. A bifunctional xanthate bis[2-(2-(O-ethyl dithiocarbonate)propionate ethoxy)-4,4′-dicarbonyl-2,2′-bipyridine] (X-bpy-X) was synthesized as a RAFT/MADIX agent to control vinyl acetate (VAc) polymerization, and then the bpy moiety was introduced into the OVAc chain successfully. A series of oligo(vinyl acetate)-bipyridine-oligo(vinyl acetate) (OVAc-bpy) with a PDI of 1.5 and a molecular weight range of 1000–3500 were obtained. The phase behaviour of OVAc-bpy in supercritical carbon dioxide (sc-CO₂) was determined by the cloud point method. Compared with OVAc homopolymers with a similar degree of polymerization (DP), OVAc-bpy has lower solubility due to the existence of bpy moieties. The lowest cloud point pressure was achieved in sc-CO₂ at M_n,GPC = 1900. OVAc-bpy was used as a ligand to extract the metal ions by using sc-CO₂ as the solvent. The extraction rate can be as high as 98% (for Ni²⁺) and reasonably good for other metal ions (Cu²⁺ and Co²⁺) without using any additive.