- Suppression of spin-spin coupling in nitroxyl biradicals by supramolecular host-guest interactions
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The use of supramolecular architectures to control the spatially dependent spin exchange (spin communication) between two covalently linked radical centers (biradical) has been explored. Cucurbit[8]uril, through supramolecular steric effect, completely suppresses spin exchange between two adjacent radical centers in a biradical. The Royal Society of Chemistry.
- Porel, Mintu,Ottaviani, M. Francesca,Jockusch, Steffen,Jayaraj, Nithyanandhan,Turro, Nicholas J.,Ramamurthy
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supporting information; experimental part
p. 7736 - 7738
(2010/11/17)
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- Ultrafast and reversible multiblock formation by the SET-nitroxide radical coupling reaction
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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 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 CuI 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-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. CSIRO 2010.
- Kulis, Jakov,Bell, Craig A.,Micallef, Aaron S.,Monteiro, Michael J.
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experimental part
p. 1227 - 1236
(2011/03/19)
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- Inhibition of polymerization of unsaturated monomers
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Disclosed herein is a method for inhibiting the premature polymerization of ethylenically unsaturated monomers comprising adding to said monomers an effective amount of a mixture comprising: A) at least one stable hindered nitroxyl compound having the structural formula: wherein R1and R4are independently selected from the group consisting of hydrogen, alkyl, and heteroatom-substituted alkyl and R2and R3are independently selected from the group consisting of alkyl and heteroatom-substituted alkyl; and X1and X2(1) are independently selected from the group consisting of halogen, cyano, COOR7, —S—COR7, —OCOR7, (wherein R7is alkyl or aryl), amido, —S—C6H5, carbonyl, alkenyl, or alkyl of 1 to 15 carbon atoms, or (2) taken together, form a ring structure with the nitrogen; and B) at least one inhibitor selected from the group consisting of ortho-quinone, ortho-hydroquinone, para-quinone, para-hydroquinone, and derivatives of the foregoing.
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- Synthesis and magnetic properties of some crystalline nitroxide radicals
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The syntheses of different nitroxide radicals are reported. The thermal behaviour of the nitroxide radicals was examined by polarizing microscopy, differential scanning calorimetry as well as X-ray diffraction experiments. Temperature dependent magnetic susceptibility measurements were carried out in order to determine the magnetic properties of these nitroxide radicals. The majority of the radicals presented here show weak antiferromagnetic exchange interactions.
- Griesar,Soto-Bustamante,Haase
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p. 567 - 575
(2007/10/03)
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