Gelation mechanism and mechanical properties of Tetra-PEG gel

Tetra-PEG gel has drawn much attention as a polymer gel with extremely suppressed heterogeneity, which is known as the intrinsic characteristics of polymer networks, and is difficult to control. Tetra-PEG gel is formed by a novel fabrication method, i.e., AB-type crosslink coupling, which is polycondensation between mutually reactive multi-armed polymers forming a polymer network. AB-type crosslink coupling has advantages on suppressing the heterogeneity over conventional polycondensation. In this review, we focused on the gelation reaction and the relationship between the mechanical properties and structure. The reaction proceeded as a simple second order reaction of A and B end-groups from the initiation to the end (approx. 90%), suggesting the homogeneous mixing of two prepolymers. The model predicting the elastic modulus of Tetra-PEG gel shifts from the phantom to affine network models with an increase in polymer concentration. The fracture energy is well predicted by the Lake-Thomas model. These experimental studies also suggest that Tetra-PEG gel has extremely homogeneous network structure and is a candidate material for evaluating the basic physical properties of polymer gels.