(363g) Charging Neutral Polymer By Simple and Macro Ions in Solution

It is recently reported that neutral polymers, such as poly (ethylene oxide) (PEO), could behave like weakly charged polyelectrolyte in highly polar solvents. We have examined the ion charging and resulting conformational structure of single PEO chains of varied molecular weight in water and mixed solvents by fluorescence correlation spectroscopy (FCS)-photon counting histogram (PCH) experiments. PCH results indicate that PEO becomes positively charged in LiCl-added solution, yet the measured electrical potential of PEO in LiCl solution decreases rapidly with the addition of multivalent polyoxometalate (POM) polyanions. The net charge of single PEO chains in solution shows strong dependence on the concentration ratio among Li+ cation, POM anion, and PEO monomer. FCS results show non-monotonic change of measured hydrodynamic size of single PEO chains in LiCl or LiCl-POM added solution with increasing ionic concentration, suggesting distinct ionic binding and screening effects. Further, the addition of a solvent with weak hydrogen-bond donor capabilities could further weaken the binding POM with PEO, but not so for the binding of Li+ cation with PEO. Therefore, the formation of PEO-Li+-POM complexes in different solvent mixture could lead to a facile process of PEO-based ionomers of tunable net charge and charge density.