Nanostructures of tetra-arm Poly(ethylene glycol) networks by Iron(III)-Catechol coordinative crosslinking units

Abstract

The internal structure of tetra-arm poly(ethylene glycol) networks crosslinked via coordination bonds was investigated to understand the structural aspects of these networks, which are connected by finite polymer units. In tetra-arm poly(ethylene glycol) modified with catechol moieties (4-PCA), the networks were preserved by coordination bonds of catechol-Fe(III) ions using optimal quantitative ratios (RCA/Fe) that form bis and tris-complexes depending on pH values. The network is established with finite units associated with changes in geometrical connections. This research focuses on the structural aspects composed of controllable coordination bonding units. The samples were investigated using small-angle X-ray scattering (SAXS) and neutron scattering (SANS) measurements. The apparent correlation lengths of the gels were discussed as the presence of nano-defects. The contrast variation SANS results support the presence of nano-defects, Rg ∼3 nm. The defects are incorporated by partial irregularity of missing linkages and subsequent distortion of the topology. The rapid and sensitive controls using metal-mediated coordination bond may generate defects in the polymer network. It suggests that diverse strategies for metal-mediated hydrogels can be found by monitoring their nanostructures.