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