writer：Mingyu Guo, Louis M. Pitet, Hans M. Wyss, Matthijn Vos, Patricia Y. W. Dankers and E. W. Meijer*
keywords：Tough Stimuli-Responsive Supramolecular Hydrogels
source：期刊
specific source：J. Am. Chem. Soc. 2014, 136, 6969-6977.
Issue time：2014年
Hydrogels were prepared with physical crosslinks
comprising 2-ureido-4[1H]-pyrimidinone (UPy) hydrogen-
bonding units within the backbone of segmented
amphiphilic macromolecules having hydrophilic poly(ethylene
glycol) (PEG). The bulk materials adopt nanoscopic physical
cross-links composed of UPy?UPy dimers embedded in segregated hydrophobic domains dispersed within the PEG matrix as comfirmed by cryo-electron microscopy. The amphiphilic network was swollen with high weight fractions of water (wH2O ≈ 0.8) owing to the high PEG weight fraction within the pristine polymers (wPEG ≈ 0.9). Two different PEG chain lengths were investigated and illustrate the corresponding consequences of cross-link density on mechanical properties. The resulting hydrogels exhibited high strength and resilience upon deformation, consistent with a microphase separated network, in which the UPy?UPy interactions were adequately shielded within hydrophobic nanoscale pockets that
maintain the network despite extensive water content. The cumulative result is a series of tough hydrogels with tunable mechanical properties and tractable synthetic preparation and processing. Furthermore, the melting transition of PEG in the dry polymer was shown to be an effective stimulus for shape memory behavior.