Viscoelastic Properties of Dynamic Chemical Crosslinking Hydrogel Based on Telechelic Macromolecular Crosslinker

Hydrogels with dynamic chemical crosslinking are obtaining more and more attention in the field of functional polymer materials. To rationally control the functions of the material, it is important to understand the relationship between viscoelastic properties and network structure comprehensively. In this work, dynamic chemical crosslinking hydrogel was prepared using chitosan as the backbone, dibenzaldehyde poly(ethylene glycol) (DF-PEG) as the macromolecular cross-linker and Schiff's base as the dynamic cross-linking bond. The network structure and the viscoelasticity were thus tailored by regulating the molecular weight and the concentration of telechelic macro-crosslinker, and the linear and non-linear rheological properties were studied with a rotational rheometer. The linear rheological results show that the storage modulus of hydrogel increases with the increase of molecular weight or the concentration of DF-PEG, because DF-PEG has higher probability to connect with two different chitosan backbones and creates elastic-active crosslinking as the molecular weight or the concentration of DF-PEG increases. The relaxation time of the hydrogels exhibits the similar dependence on the molecular weight or the concentration of DF-PEG, in reminiscent of the "Sticky Reptation" mechanism of associative polymer chains. An interesting shear thickening phenomenon is observed on the as-prepared hydrogel, and the magnitude of shear-thickening decreases with the increase of concentration or the molecular weight of DF-PEG. It can be explained by a mechanism of shear-induced transition from non-elastic-active crosslinker to elastic-active crosslinker. The current study unveiled the relationship between network structure and viscoelasticity of hydrogel, which would guide the design of functional hydrogels.