Small dop of comonomer, giant shift of dynamics: α-methyl-regulated viscoelasticity of poly(methacrylamide) hydrogels

• Incorporating a small amount (≤6 mol%) of α -methyl-absent monomer, acrylamide into polymethacrylamide hydrogels significantly alters their viscoelasticity, • The α -methyl-absent monomer acts as a hydrophilic defect, enhancing water molecule dynamics and accelerating polymer chain dissociation. • Modulating the α -methyl-regulated dynamic properties enables the development of copolymer hydrogels with rapid self-healing capabilities and tunable adhesion. α -Methyl groups play significant roles in the regulation of water molecules within both small molecular systems and bio-macromolecular systems. Systematically studying the influence of α -methyl on the dynamics of water molecules within hydrogel systems is therefore worthwhile. In this study, we prepared a series of hydrogen-bonded (H-bonded) hydrogels with varying densities of α -methyl groups by copolymerizing methacrylamide (MAm) with its α -methyl-absent analogue, acrylamide (Am). Introducing a small amount of Am (≤6 mol%) into the polymer chain resulted in significant shifts in the viscoelasticity of the hydrogels. The hydrogels exhibit a “time-temperature- α -methyl equivalence”, meaning that introduction of α -methyl-absent monomer has effects similar to elevating temperature and prolonging observation time on the dynamic properties. Based on low-field nuclear magnetic resonance spectroscopy and Raman scattering, a “hydrophilic defects-assisted H-bonds dissociation” mechanism is proposed, depicting that the α -methyl-absent monomer can disturb the rearrangement of water molecules surrounding the polymer chain and accelerate chain dissociation. These findings enabled the copolymer hydrogels with functions such as fast self-healing and tunable interface adhesion.