Abstract
Investigation of the curing kinetics of crosslinking reactions and the development of optimized catalyst systems is of importance for the preparation of self-healing nanocomposites, able to significantly extend their service lifetimes. Here we study different modified low molecular weight multivalent azides for a capsule-based self-healing approach, where self-healing is mediated by graphene-supported copper-nanoparticles, able to trigger “click”-based crosslinking of trivalent azides and alkynes. When monitoring the reaction kinetics of the curing reaction via reactive dynamic scanning calorimetry (DSC), it was found that the “click-crosslinking” reactivity decreased with increasing chain length of the according azide. Additionally, we could show a remarkable “click” reactivity already at 0 °C, highlighting the potential of click-based self-healing approaches. Furthermore, we varied the reaction temperature during the preparation of our tailor-made graphene-based copper(I) catalyst to further optimize its catalytic activity. With the most active catalyst prepared at 700 °C and the optimized set-up of reactants on hand, we prepared capsule-based self-healing epoxy nanocomposites.
Highlights
Self-healing approaches do have a significant potential in polymeric materials, especially those based on embedded capsule systems [1]
A two-necked round-bottom flask equipped with magnetic stir bar, rubber septum and gas tap was heated under vacuum and flushed with nitrogen several times. 4-Dimethylaminopyridine (0.2 eq) was added to 2 (1.0 eq) dissolved in dry DMF and the solution was stirred for ten minutes at room temperature
While comparing the different catalysts prepared at 300 to 800 ◦ C, it was observed that the onset temperature (Tonset) and Tp decreased with increasing temperature applied during the reduction of copper(II)-modified graphene oxide towards TRGO-Cu2 O, in line with the expectation and the increasing size of the formed copper particles
Summary
Self-healing approaches do have a significant potential in polymeric materials, especially those based on embedded capsule systems [1]. The molecular design of such self-healing materials requires fast and efficient crosslinking processes, which often are afforded by catalytic reactions using homogeneous and heterogeneous chemistry [2]. We recently reported on a “click”-based crosslinking chemistry useful as a principle for optimized self-healing materials [12] In this particular system, multivalent azides and alkynes are crosslinked by the use of a Cu(I)-catalyst, acting as the known essential catalytic system for “click”-chemistry [12,49,50,51,52,53]. For a capsule-based self-healing approach, the encapsulation of the azides required a careful tuning of their hydrophobicity It was unclear though, how and whether small changes in the azide-monomer would change its reactivity within the same click-system. In this study we investigate the influence of small substitutions within the trivalent azides on the reaction kinetics investigated via DSC as well as in view of different homogeneous and heterogeneous copper(I) catalysts
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