Kinetic analysis of nitroxide radical coupling reactions mediated by CuBr

End-functionalized polymers by controlled/living radical polymerizations: synthesis and applications

This review focuses on end-functionalized polymers synthesized by controlled/living radical polymerizations and the applications in fields including bioconjugate formation, surface modification, topology construction, and self-assembly.

In the (Very) Long Run We Are All Dead: Activation and Termination in SET-LRP/SARA-ATRP

The rate constants of activation and termination were determined for SET-LRP/SARA-ATRP polymerizations of methyl acrylate. Measurement of the rate of generation of CuBr₂ throughout the reaction (using data from Levere et al., Macromolecules 2012, 45, 8267-8274) allowed evaluation of the chain length dependence of the two rate constants, which were found to be 1.25(9) × 10^-4DP_n^-0.51(3) cm·s^-1 (activation) and 3.1(1) × 10⁹DP_n^-0.49(2) L·mol^-1·s^-1 (termination). Addition of the CuBr₂ deactivator at the beginning of the reaction is found to result in a higher proportion of dead chains due to rapid termination of short chains.

Construction of a 3-Miktoarm Star from Cyclic Polymers

Cyclic polymers have intriguing physical properties, including those found in biological membranes for greater temperature, salt and acid stability. Although, many unique and complex synthetic cyclic structures have been prepared, there are no reports of ABC miktoarm stars constructed of three cyclic polymers with very different chemical compositions. We report such a structure in one pot at 25 °C by modulating the copper catalyst activity using combinations of solvents and ligands.

Ultrafast and Reversible Multiblock Formation by the SET-Nitroxide Radical Coupling Reaction

The single electron transfer-nitroxide radical coupling (SET-NRC) reaction has been used to produce multiblock polymers with high molecular weights in under 3 min at 50°C by coupling a difunctional telechelic polystyrene (Br-PSTY-Br) with a dinitroxide. The well known combination of dimethyl sulfoxide as solvent and Me6TREN as ligand facilitated the in situ disproportionation of CuIBr to the highly active nascent Cu0 species. This SET reaction allowed polymeric radicals to be rapidly formed from their corresponding halide end-groups. Trapping of these carbon-centred radicals at close to diffusion controlled rates by dinitroxides resulted in high-molecular-weight multiblock polymers. Our results showed that the disproportionation of CuI was critical in obtaining these ultrafast reactions, and confirmed that activation was primarily through Cu0. We took advantage of the reversibility of the NRC reaction at elevated temperatures to decouple the multiblock back to the original PSTY building block through capping the chain-ends with mono-functional nitroxides. These alkoxyamine end-groups were further exchanged with an alkyne mono-functional nitroxide (TEMPO–≡) and ‘clicked’ by a CuI-catalyzed azide/alkyne cycloaddition (CuAAC) reaction with N3–PSTY–N3 to reform the multiblocks. This final ‘click’ reaction, even after the consecutive decoupling and nitroxide-exchange reactions, still produced high-molecular-weight multiblocks efficiently. These SET-NRC reactions would have ideal applications in re-usable plastics and possibly as self-healing materials.