Jakov Kulis

A comparative study of the SET-LRP of oligo(ethylene oxide) methyl ether acrylate in DMSO and in H2O

A comparative analysis of the SET-LRP of oligo(ethylene oxide) methyl ether acrylate (OEOMEA) in DMSO and in H2O at 25 °C is reported. Both the catalysis with activated Cu(0) wire/Me6-TREN and with mimics of “nascent” Cu(0) nanoparticles/Me6-TREN resulted in a higher rate of polymerization in water than in DMSO. This result is consistent with the acceleration expected for SET-LRP by a more polar reaction solvent, and with the difference between the equilibrium constants of disproportionation of CuBr in DMSO (Kd = 1.4–4.4) and in water (Kd = 106 to 107), both much higher in the presence of Me6-TREN. The inefficient access of the Cu(0) catalyst to the hydrophobic reactive centers of the monomer and initiator assembled in micellar structures explains the induction time observed in the SET-LRP of OEOMEA in water. This induction period is longer for Cu(0) wire. The use of “nascent” Cu(0) nanoparticles prepared by the disproportionation of CuBr in DMSO, in combination with 5 mol% CuBr2, led to an extremely efficient SET-LRP of OEOMEA in water. This SET-LRP in water is fast and follows first order kinetics to complete monomer conversion with linear dependence of experimental Mn on conversion, and narrow molecular weight distribution. Under the polymerization conditions investigated in both water and DMSO, no reduction in the absorbance of CuBr2/Me6-TREN was observed by online UV-vis spectroscopy. This excludes the formation of CuBr by reduction of CuBr2 by Cu(0) during the SET-LRP in DMSO and in water.

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.

Synthesis of dianionic and trianionic chiral, chelating ligands based on amino acids

The synthesis of two new families of amino acid-containing chiral ligands, based on methyliminodiacetic acid and nitrilotriacetic acid cores, has been accomplished using a simple protection, solution phase amide coupling and deprotection strategy. The amino acids glycine, leucine, aspartic acid and phenylalanine were used to demonstrate the versatility of the synthetic route, and that no epimerisation occurs. Thus, the tridentate ligands bear C3 symmetry, while the bidentate ligands have C1 symmetry.