Systematic Investigation of a Crown Ether Functionalized PS-b-PMAA Block Copolymer for Optimized Lithium Extraction from Aqueous Media

Crown ether (CE) functionalized polystyrene-block-poly(methacrylic acid) (PS-b-PMAA) material (PS-b-P(MAA-r-CE3MA)) forms lithium-CE sandwich complexes with high selectivity. The complexation strength of PS-b-P(MAA-r-CE3MA) was determined in a two-phase extraction. A two-step one-pot RAFT polymerization in water was used to synthesize the block copolymers, in which the macro-RAFT agent (PMAA) produced in the first step was polymerized with styrene in an emulsion polymerization in the second step. Subsequently, the MAA block was partially esterified with the functionalized CE. The polymer structure was varied for investigating the influence of the degree of polymerization (DP) of the overall polymer, the DP of the PS, and the functionalization density with regard to increasing the effectiveness of lithium complexation. Based on the observed trends, it was possible to optimize the system toward a significantly improved lithium complexation compared to free CE (by a factor of up to 4 × 10⁸).