Because of the environmental issues associated with thermoset or network polymers, recyclable polymers are highly in demand, and the use of sustainable biomass-derived ingredients is also becoming increasingly important. In this work, we utilized 2,5bis(hydroxymethyl)furan as a starting material to produce network polyurethanes (NPUs) under facile, solvent-free (solid-state) ball milling conditions. Urethane bonds may undergo thermally controlled transcarbamoylation, a reversible dynamic covalent bond exchange, enabling reshaping of NPUs. Taking advantage of this chemistry, we demonstrate the self-healing, reprocessing, and shapememory properties of biomass-derived NPU films using mesoerythritol as a cross-linking agent. Interestingly, in urethane-bondforming reactions, the relative reactivity of the secondary alcohol group of meso-erythritol over the primary one is remarkably different in the solid state, resulting in NPU films with much enhanced mechanical properties. Dynamic mechanical thermal and stress relaxation analyses indicate that the NPU films possess typical characteristics of vitrimers, such as constant cross-link density and Arrhenius-like reduction in viscosity at elevated temperatures, even though the dissociative exchange of urethane bonds may work here. Our mechanochemical approach is facile and scalable, enabling the preparation of sustainable and recyclable polymers from various biomass-derived chemicals.
Electroconductive hydrogels are composed of 3-dimensionally structured hydrogels and conducting molecules with electrical, optical, and reversible redox properties. These hybrid materials can be utilized as electrically-stimulated biomaterials in implantable biosensors or drug delivery systems. In this study, carbon nanotube-incorporated polyvinyl alcohol (PVA)-based hydrogels were synthesized by an electroclick reaction, which was controlled by an electrochemically generated Cu(I) catalyst. When the reduction potential of Cu(II) ions was applied, PVA-based hydrogels were deposited onto indium-tin-oxide-coated glass electrodes via Cu(I)-catalysed alkyne-azide cycloaddition (click reaction). When the hydrogels contained carbon nanotubes, thicker films were deposited because the embedded carbon nanotubes provided a larger electrochemical active area. In addition, the carbon nanotubes improved the electrical conductivity of the hydrogel systems. We investigated the electro-stimulated drug release behaviour with electro-click conductive hydrogels using tetracycline as a model drug. † Electronic supplementary information (ESI) available: The SEM image of ITOcoated glass after the gelation reaction without a bis-azide crosslinker (Fig. S1); the cyclic voltammogram of a CNT/PVA click solution (Fig. S2); the cyclic voltammogram of Fe(CN) 6 3− with different scan rates (Fig. S3); UV-vis spectra of tetracycline (Fig. S4); the release profile of tetracycline from PVA hydrogel film without CNTs (Fig. S5). See
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