A new approach to the green synthesis of imidazole-containing polymer ligands and cryogels

Here we propose a new approach to the synthesis of polyallylamine (PAA) and polyethylenimine (PEI) derivatives containing 5-methyl-4-imidazolyl moiety. The developed approach is based on usage of an effective method of polymer transformation under "synthesis in gel" conditions in aqueous solutions under reflux via interactions of aminopolymers with 5-methyl-4-imidazolylmethanol as a non-standard reagent for nucleophilic substitution. Nontoxicity of the alkylating agent and transformation in aqueous medium assure significant preparative advantages and eco-friendliness of this approach to the synthesis of imidazole-containing polymers. It was found that N-functionalization proceeds simultaneously with cross-linking of the derivatives; however, using pre-crosslinked PAA cryogels, the same functionalization strategy can be applied to obtain highly porous materials. The composition of the derivatives was characterized using the elemental analysis and thermo. gravimetry with FT-IR identification of gaseous destruction products. The structure of the derivatives was confirmed using the FT-IR spectroscopy and C-13 and N-15 NMR spectroscopy in the solid state. The resulted imidazole-containing derivatives of PAA (IMPAA) and PEI (IMPEI) were compared with the imidazolylmethyl derivative of natural aminopolymer chitosan (IMC) and unmodified polymers (PAA, PEI, and chitosan) in terms of the Ni(II) ions sorption. It was demonstrated that that introduction of imidazolylmethyl groups remarkably increases sorption capacity of all polymers toward Ni(II) ions, which is changed depending on the polymer structure in the following order: IMPEI > IMC > PEI > IMPAAcryogel > IMPAA > PAA.