Supramolecular H-bonded three-arm star polymers by efficient combination of RAFT polymerization and thio-bromo “click” reaction

Efficient and versatile "click"-based post-polymerization tools for the straightforward modification of especially polymers with sophisticated architectures play a significant role in polymer chemistry. We here report on the synthesis of supramolecular three-arm star polymers by a combination of RAFT polymerization and the thio-bromo "click" reaction, consequently exploring the potential of this particular thiol-halogen "click" reactions as post-polymerization tool. Therefore, two new trivalent chain transfer agents (CTAs) bearing either trithiocarbonate or dithiobenzoate groups were designed and investigated for the RAFT polymerization of n-butyl acrylate (nBA) and styrene. Kinetic investigations of CTA/monomer combinations were performed to obtain star-shaped poly(n-butyl acrylate)s (PnBA) and poly(styrene)s (PS) with adjustable molecular weights and well controllable polydispersities in the range of 1.13-130. The capped thiol-groups were released by aminolysis and quantitatively converted into barbiturate or imidazolium end-groups, allowing to prepare functionalized supramolecular star polymers via this particular thio-bromo "click" reaction. Thereby, the best results for aminolysis were not obtained in a one-pot reaction as expected but in a two step process, while acetonitrile has been shown to be essential for the success of the reaction in contrast to the pKa-value of the investigated bases. As proven via NMR spectroscopy and mass spectrometry all desired supramolecular star polymers were obtained with an exceptional high extend of end-group functionality (>95%) underscoring the potential of this specific "click"-based post-polymerization modification tool in combination with RAFT polymerization. (C) 2017 Elsevier Ltd. All rights reserved

Improving Kinetics of “Click-Crosslinking” for Self-Healing Nanocomposites by Graphene-Supported Cu-Nanoparticles

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

Carbon-Supported Copper Nanomaterials: Recyclable Catalysts for Huisgen [3+2] Cycloaddition Reactions

Highly disperse copper nanoparticles immobilized on carbon nanomaterials (CNMs; graphene/carbon nanotubes) were prepared and used as a recyclable and reusable catalyst to achieve CuI-catalyzed [3+2] cycloaddition click chemistry. Carbon nanomaterials with immobilized N-heterocyclic carbene (NHC)-Cu complexes prepared from an imidazolium-based carbene and CuI show excellent stability including high efficiency at low catalyst loading. The catalytic performance evaluated in solution and in bulk shows that both types of Cu-CNMs can function as an effective recyclable catalysts (more than 10cycles) for click reactions without decomposition and the use of external additives