Synthesis and Properties of Physically Cross-Linked Hydrogel Obtained from Linear Polymer

Chemically crosslinked gels typically have a low toughness because of inefficient energy dissipation. Increasing the amount of covalent crosslinks improves the stiffness of the gel but makes it brittle. Gels that are physically crosslinked are comparatively tougher due to better viscoelastic energy dissipation produced by non-covalent, polar, and ionic interactions.^{1, 2} In addition, they are processable and can be molded in to desired shape unlike covalently crosslinked gel. We achieved hydrophobically modified hydrogels (HPMHs), in which hydrophobic groups act as physical crosslinking sites, show a dramatic increase in the storage modulus (G’)  and the loss modulus (G”) compared to the conventional physical hydrogels. However, the strength of HPHMs increases with increasing concentration of the hydrophobic species and decreases with increasing hydrophilic monomer content in the polymer backbone.³ However, the swelling ratio increases with decreasing hydrophobic content. The HMHs we obtained are stable till 200 ^oC. Nevertheless, The HMHs also show thermoresponsive behavior in swollen state.

References:

1. Ajayaghosh, A.; George, S, J. J. Am. Chem. Soc. 2001, 123 , 5148–514

2. Sun, J. Y.; Zhao, X.; Illeperuma, W. R. K.; Chaudhuri, O.; Oh, K. W.; Mooney, D. J.; Vlassak, J. J.; Suo, Z. Nature 2012, 489, 133-136

3. Hao, J.; Weiss, R. A.; Macromolecules 2011, 44, 9390–9398