Regulating Dynamics of Polyether-Based Triblock Copolymer Hydrogels by End-Block Hydrophobicity

The relaxation dynamics of poly(ethyl glycidyl ether-co-isopropyl glycidyl ether-b-ethylene oxide-b-ethyl glycidyl ether-co-isopropyl glycidyl ether) triblock copolymer hydrogels were investigated as a function of the end-block hydrophobicity and temperature primarily using the oscillatory rheometer, which is crucial to understand the unique viscoelastic behaviors including injectability and self-healing property of the self-assembled hydrogels. Lower critical solution temperature behavior of the poly(alkyl glycidyl ether) end-blocks was harnessed by random copolymerization of poly(ethyl glycidyl ether) (EGE) and poly(isopropyl glycidyl ether) (iPGE), resulting in the remarkable temperature responsiveness of the hydrogel. As the fraction of hydrophilic monomer (i.e., EGE) increases, the sol-to-gel transition occurs at higher temperature and higher polymer concentration. The hydrogel relaxation measured by the oscillatory rheometer becomes faster with decreasing temperature and increasing fraction of hydrophilic monomers. In particular, we observed that a small increment of the hydrophilic monomer fraction significantly reduces the unfavorable interaction between the end-block and aqueous media, resulting in faster hydrogel relaxation dynamics. All polyether-based hydrogels showed biocompatibility and injectability, indicating promising soft materials for biological and biomedical applications. The results are discussed in terms of the current understanding of self-assembled triblock copolymer hydrogels, and particular attention is paid to the issue of chain dynamics.