Application of Redox-Responsive Hydrogels Based on 2,2,6,6-Tetramethyl-1-Piperidinyloxy Methacrylate and Oligo(Ethyleneglycol) Methacrylate in Controlled Release and Catalysis.

Miriam Khodeir,He Jia,Jean-François Gohy,Alexandru Vlad

doi:10.3390/polym13081307

Miriam Khodeir, He Jia + Show 2 more

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https://doi.org/10.3390/polym13081307

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Journal: Polymers	Publication Date: Apr 16, 2021
Citations: 4	License type: CC BY 4.0

Affiliation: Université Catholique de Louvain

Abstract

Hydrogels have reached momentum due to their potential application in a variety of fields including their ability to deliver active molecules upon application of a specific chemical or physical stimulus and to act as easily recyclable catalysts in a green chemistry approach. In this paper, we demonstrate that the same redox-responsive hydrogels based on polymer networks containing 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) stable nitroxide radicals and oligoethylene glycol methyl ether methacrylate (OEGMA) can be successfully used either for the electrochemically triggered release of aspirin or as catalysts for the oxidation of primary alcohols into aldehydes. For the first application, we take the opportunity of the positive charges present on the oxoammonium groups of oxidized TEMPO to encapsulate negatively charged aspirin molecules. The further electrochemical reduction of oxoammonium groups into nitroxide radicals triggers the release of aspirin molecules. For the second application, our hydrogels are swelled with benzylic alcohol and tert-butyl nitrite as co-catalyst and the temperature is raised to 50 °C to start the oxidation reaction. Interestingly enough, benzaldehyde is not miscible with our hydrogels and phase-separate on top of them allowing the easy recovery of the reaction product and the recyclability of the hydrogel catalyst.

Highlights

Hydrogels are three-dimensional, hydrophilic, polymeric networks capable of swelling in aqueous medium and resembling to some extent living tissues [1]
TEMPO groups can undergo reversible oxidation-reduction reactions that lead to redox activity while oligoethylene glycol methyl ether methacrylate (OEGMA) groups are hydrophilic and allow water swelling in order to obtain hydrogels
The nitroxide radical units of TEMPO were oxidized into oxoammonium groups (TEMPO+) with NaClO in the presence of HBF4

Summary

Introduction

Hydrogels are three-dimensional, hydrophilic, polymeric networks capable of swelling in aqueous medium and resembling to some extent living tissues [1]. They may be chemically stable or they may degrade or dissolve under specific conditions [2]. The so-called permanent or chemical hydrogels are obtained from covalently-crosslinked networks and generally present a better homogeneity than physical gels [2]. As far as biomedical applications are concerned, hydrogels derived from bio-based polymers are attracting since those polymers are generally biocompatible and biodegradable and often show a high level of biomimicry, a highly desired characteristic for in vivo applications [8]. In order to reach the desired properties with ever increasing complexity, polymer-based hydrogels may be mixed with other polymeric or non-polymeric components to form composite hydrogel systems, including e.g., polymer nanoparticles, electrospun fibers, nanocarbons, etc. [8,9,10]

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