Synthesis and characterisation of redox hydrogels based on stable nitroxide radicals

Abstract

Redox hydrogels are obtained by introducing into a poly(oligoethyleneglycol)methacrylate network 2,2,6,6-tetramethyl-1-piperidinyloxy radicals, which can be oxidized into oxoammonium cations.

Temperature and Redox‐Responsive Hydrogels Based on Nitroxide Radicals and Oligoethyleneglycol Methacrylate

“…P(TEMPO‐ r ‐OEGMA) hydrogels with different X TEMPO and X CL equal to 0.03 ( Figure ) were synthesized using the same experimental protocol as described in our previous report. [ 12 ] X CL was set to 0.03 since the accordingly obtained hydrogels present the highest swelling factor (defined as [( W s – W d )/ W d ] where W s is the weight of the hydrogel in the swollen state at equilibrium and W d is the weight of the hydrogel in the dry state) with a value around 35 (meaning that 0.025 g of gel absorb 1 g of water) for a P(TEMPO‐ r ‐OEGMA) hydrogel with X TEMPO = 0.2. Lower X CL eventually leads to viscous fluids instead of gels (Table S1, Supporting Information) and lower swelling factors are observed for higher X CL .…”

“…[ 12 ] Furthermore, cyclic voltammetry measurements confirmed the presence of redox responsive TEMPO groups in our materials and the reversibility of the redox reactions. [ 12 ]…”

“…In order to get some additional information about the structure of the gel, soluble fractions of the investigated hydrogels have been extracted and further analyzed by dynamic light scattering (DLS). Indeed, as demonstrated in our previous report, [ 12 ] our hydrogels are slightly chemically crosslinked and therefore contain a significant fraction of free or slightly crosslinked chains that can be extracted from the equilibrated hydrogels by bringing them into contact in an aqueous phase. In our previous report, the fraction of extracted was further quantified by 1 H NMR using an internal standard.…”

“…In a previous very recent study on this system, we have focused on the effects of the covalent crosslinking degree and of the content of TEMPO units on the properties of the hydrogels at room temperature. [ 12 ] We have demonstrated that the optimum molar fraction of crosslinker, X CL , is equal to 0.03 in order to obtain homogeneous gels displaying high swelling ratios. By varying the amount of TEMPO units (expressed as X TEMPO molar fraction) in the hydrogels, we have confirmed that our hydrogels are slightly chemically crosslinked systems further reinforced by physically crosslinked nanodomains resulting from the aggregation of hydrophobic TEMPO units.…”

“…By varying the amount of TEMPO units (expressed as X TEMPO molar fraction) in the hydrogels, we have confirmed that our hydrogels are slightly chemically crosslinked systems further reinforced by physically crosslinked nanodomains resulting from the aggregation of hydrophobic TEMPO units. [ 12 ] Here, our aim is to decipher the effects of temperature and redox stimuli on the rheological properties of reduced P(TEMPO‐ r ‐OEGMA) and oxidized P(TEMPO + ‐ r ‐OEGMA) hydrogels with varying TEMPO content at a fixed covalent crosslinking degree.…”