The Kinetics of Growth of Metallo-supramolecular Polyelectrolytes in Solution.

Several transition metal ions, like Fe2+ , Co2+ , Ni2+ , and Zn2+ complex to the ditopic ligand 1,4-bis(2,2':6',2''-terpyridin-4'-yl)benzene (L). Due to the high association constant, metal-ion induced self-assembly of Fe2+ , Co2+ , and Ni2+ leads to extended, rigid-rod like metallo-supramolecular coordination polyelectrolytes (MEPEs) even in aqueous solution. Here, we present the kinetics of growth of MEPEs. The species in solutions are analyzed by light scattering, viscometry and cryogenic transmission electron microscopy (cryo-TEM). At near-stoichiometric amounts of the reactants, we obtained high molar masses, which follow the order Ni-MEPE≈Co-MEPE<Fe-MEPE. The experiments indicate that the kinetics of MEPE growth follows a reversible step-growth mechanism. The forward polymerization rate constants follow the order Co-MEPE<Fe-MEPE<Ni-MEPE and the growth of MEPEs can be accelerated by adding potassium acetate.