This study explored crosslinking geometry effects on poly(ethylene glycol) networks. Tetra-poly(ethylene glycol) with catechol end groups (4-PCA) was crosslinked through coordination bonds between catechol moieties and Fe(III) ions, which produce bis-complex and tris-complex depending on pH levels. The structure and property of 4-PCA gels were examined upon the bonding types controlled by pH levels and molar ratios between catechol groups and Fe(III) ions. The coordination bond types were probed by UV absorption peaks and Raman spectra. The correlation lengths (ξ) were determined in the semi-dilute solution regime and the PCA gel networks using light scattering, small-angle X-ray scattering, and neutron scattering measurements. For the gels with bis-complex units, ξ values correspond to the size of a single polymer chain. Otherwise, they increased in the gels consisting of tris-complex units, indicating that the matrices have partial crosslinks. Viscoelastic performances of 4-PCA gels are in good agreement with structural differences, showing that typical gel-like behavior was observed in the gels with bis-complex bonds. The results show structures and properties of gels can be controlled by geometries of crosslinking units as a strategy to develop novel polymer gels.

Structures and properties of poly(ethylene glycol) hydrogels controlled by geometries of crosslinking units

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