Redox-induced polymerisation/depolymerisation of metallo-supramolecular polymers

Abstract

Redox-responsive metallo-supramolecular polymers (MSPs), consisting of a ditopic ligand end-capped poly(tetrahydrofuran) (pTHF) macromonomer self-assembled with copper ions, have been developed where the degree of polymerization of the MSP, and therefore the viscosity of its solutions, depends on the oxidation state of the copper ion. We use a combination of UV-Vis, viscosity, light scattering, cyclic voltammetry and SAXS to show that the ligands, 2,6-bis(N-methylbenzimidazolyl)pyridine (MeBip), at the ends of the pTHF, bind copper(II) in a 2 : 1 ratio and copper(I) in a 2 : 2 ratio in solution. Thus at fixed 1 : 1 or 1 : 2 stoichiometry of macromonomer to copper ions the viscosity of their solutions shows dramatic changes in response to addition of a chemical oxidant (nitroso tetrafluoroborate) or reductant (aqueous ascorbic acid).