Dynamic Geometry and Kinetics of Polymer Confined in Self-Assembly via Cooperative Hydrogen Bonding: A Solid-State NMR Study under Paramagnetic Doping

Paramagnetic doping was used to enhance the sensitivity of NMR for poly(ethylene oxide) (PEO)-UREA self-assemblies without disturbing their structures and thermal properties. Bis(2,4-pentanedionato) Cu(II) (Cu(II)-AA), a paramagnetic compound, was added to the solution after the supramolecular particles had formed. At a low concentration, the T1H value rapidly decreased with increasing Cu(II)-AA wt %. However, the T1H value was almost saturated at concentrations higher than 1wt%. At 5 wt%, doping effects on local structure and thermal property were investigated. The 13C line widths for PEO and UREA signals did not change with the doping. DSC scan also showed the characteristic melting peak corresponding to the supramolecular crystals at 416 K, with melting of some excess UREA crystals at 407 K. These structural results and T1H behaviors suggest that the Cu(II)-AA molecules simply attach to the surface and reduce the T1H value due to a fast spin diffusion into the interior region without disturbing the bulk structures and thermal properties.