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

Abstract

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 Me 6 TREN as ligand facilitated the in situ disproportionation of Cu I Br to the highly active nascent Cu 0 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 Cu I was critical in obtaining these ultrafast reactions, and confirmed that activation was primarily through Cu 0 . 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 Cu I -catalyzed azide/alkyne cycloaddition (CuAAC) reaction with N 3 -PSTY-N 3 to reform the multiblocks. This final 'click' reaction, even after the consecutive decoupling and nitroxide-exchange reactions, still produced highmolecular-weight multiblocks efficiently. These SET-NRC reactions would have ideal applications in re-usable plastics and possibly as self-healing materials.

Synthesis of amphiphilic ABC triblock copolymers by single electron transfer nitroxide radical coupling reaction in tetrahydrofuran

“…This reaction is termed as SETNRC reaction 41. Later, SETNRC reaction strategy is successfully applied in macromolecular chemistry, offering polymeric materials ranging from the block41 copolymers to the complex macromolecular structures like star,42 multiblock,43 and cyclic polymer 44. We investigated the effect of temperature, catalyst system, and the structure of bromine‐connected groups on the coupling reaction in dimethylformamide (DMF) 45.…”

Introduction: Charting the landscape of cancer survivors' health‐related outcomes and care

“…ATNRC reaction of GS‐TEMPO with well‐defined Br‐terminated PNIPAM homopolymer was preformed in the presence of CuBr/PMDETA at room temperature for 4 days using DMF/H 2 O (v:v = 1:1) as solvent. Another coupling approach, single electron transfer‐nitroxide radical coupling (SET‐NRC),50–52, 59–64 was also attempted by using cheaper Cu 0 powder instead of CuBr as catalyst. However, we did not obtain the desired product.…”

Post‐polymerization modification by nitroxide radical coupling

“…Later, the same group extended the method to quadruple click reactions including thiol‐ene for the preparation of cysteine‐terminated linear PS‐ b ‐PCL‐ b ‐PMMA‐ b ‐PEG copolymers . Other interesting examples of multiblock linear copolymers obtained with this strategy have also been reported …”

“…described the use of different functional TEMPO derivatives to functionalize PS‐Br working at 25 °C with CuBr/tris(2‐dimethylaminoethyl) amine (Me 6 TREN) as the catalytic system and with toluene/DMSO as solvent (Scheme ). Later the method was expanded to P t BA‐Br and Br‐PS‐Br polymers using different functional TEMPO‐based compounds . These NRC reactions were completed in less than 10 min obtaining chain‐end functionalized polymers with functionalities above 90% and near‐quantitative coupling efficiency.…”