Nitro-group functionalization of dopamine and its contribution to the viscoelastic properties of catechol-containing nanocomposite hydrogel

X Ding, GK Vegesna, H Meng, A Winter, BP Lee*
March 19, 2015
Macromolecular Chemistry and Physics, 216, 1109-1119, 2015.

Linear polyacrylamide (PAAm) was modified with dopamine or nitrodopamine (PAAm-D and PAAm-ND, respectively) to evaluate the effect of nitro-group modification on the interfacial binding properties of polymer-bound catechol. Nanocomposite hydrogels were prepared by mixing PAAm-based polymers with Laponite and the viscoelastic properties of these materials were determined using oscillatory rheometry. Incorporation of small amount of catechol (~0.1wt% in swollen hydrogel) drastically increased the shear moduli by 1–2 orders of magnitude over those of catechol-free control. Additionally, PAAm-ND exhibited higher shear moduli values than PAAm-D across all the pH range tested (pH 3.0–9.0). Base on the calculated effective crosslinking density, effective functionality, and molecular weight between crosslinks, nitro-group functionalization of dopamine resulted in a polymer network with increased crosslinking density and crosslinking points with higher functionality. Nitro-functionalization enhanced the interfacial binding property of dopamine and increased its resistant to oxidation, which resulted in nanocomposite hydrogels with enhanced stiffness and viscous dissipation property.

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