Single Electron Transfer-nitroxide Radical Research Articles

Tadpole-shaped polymers based on UV-induced strain promoted azide-alkyne cycloaddition reaction

In the present study, we synthesized well-defined tadpole-shaped polystyrene (PS) via the combination of atom transfer radical polymerization (ATRP) and UV-induced strain promoted azide-alkyne cycloaddtion (SPAAC) reaction. A di-bromo ATRP initiator (Br-ini-Br) containing cyclopropenone-masked dibenzocyclooctyne group was used to prepare the linear PS with a cyclopropenone-masked dibenzocyclooctyne in the middle of the chain and bromo groups at both ends (Br-PS-Br). Then we used the single electron transfer-nitroxide radical coupling (SET-NRC) reaction to transfer the bromo end groups to azide groups (N3-PS-N3). After UV irradiation, the dibenzocyclooctyne group was quantitatively released, and intramolecularly reacted with alternative azide end group to produce the tadpole-shaped PS based on SPAAC reaction.

Methods for Synthesizing the Macromolecular Constituents of Smart Nanosized Carriers for Controlled Drug Delivery

Smart multifunctional polymeric nanocarriers able to respond to physicochemical changes in their environment or to external stimuli represent a new paradigm in the field of pharmaceutical formulations for controlled drug delivery. The introductory part of the present review deals with this new concept and presents the main advantages resulting from the use of such nanovehicles instead of conventional, much larger drug delivery systems. The access to drug nanocarriers based on smart supramolecular polymeric materials is primarily limited by the available polymerization methods capable to produce polymers with low polydispersity index, as well as much more complex macromolecular architectures with strictly controlled chemical composition, such as block copolymers and star or graft polymers or copolymers. This article reviews the state-of-the art in controlled/"living" free radical polymerization techniques as well as ring opening polymerization methods. Nitroxide mediated free radical polymerization (NMP), atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain-transfer polymerization (RAFT), single electron transfer-living radical polymerization (SET-LRP), single electron transfer-nitroxide radical coupling reaction (SET-NRC), cationic ring opening polymerization (CROP), anionic ring opening polymerization (AROP), and metal catalyzed ring opening polymerization are described, highlighting their mechanistic details and their synthetic potential as well as their limitations. The final part of the article is dedicated to a special type of unimolecular, monodisperse nanocarriers - the dendrimers. Both divergent and convergent approaches to dendrimer synthesis are described along with the therapeutic applications taking advantage of the unique branched tree-like globular structure of dendrimers to treat cancer.

ATNRC/SET-NRC synthesis of graphene/polyisobutylene nanocomposites

Two polyisobutylene-grafted graphene nanocomposites were prepared by CuBr-catalyzed atom transfer nitroxide radical coupling (ATNRC) and Cu-catalyzed single electron transfer-nitroxide radical coupling (SET-NRC) chemistry under mild conditions, respective

Nitroxide radical coupling reaction: a powerful tool in polymer and material synthesis

The aim of this review is to summarize and highlight the rapidly expanding area of nitroxide radical coupling reactions, including atom transfer nitroxide radical and single electron transfer nitroxide radical coupling reactions, in polymer and material synthesis. Initial discussion is focused on the influencing factors, e.g. temperature, solvent, catalyst and the structure of reactant, on the reaction rate and efficiency. In addition, this review attempts to demonstrate the broad applications of nitroxide radical coupling reactions on the terminal functionalization of polymers, the synthesis of polymers with complex and well-defined architecture, and the preparation of organic–inorganic composites. Finally, the current challenges and future directions of nitroxide radical coupling reactions are also discussed.

One-pot synthesis of chitosan-g-(PEO-PLLA-PEO) via “click” chemistry and “SET-NRC” reaction

For the development of biocompatible and degradable biomaterials, a kind of well-defined graft copolymer consisting of chitosan back-bone and amphiphilic PEO-PLLA-PEO branch chains was synthesized by Cu(0) catalyzed one-pot strategy combining “click” chemistry and single electron transfer-nitroxide radical coupling (SET-NRC) reaction. First, the precursors of 6-azide-N-phthaloyl-chitosan, TEMPO-PEO-alkyne and mPEO-PLLA-Br were designed and produced. Then, the one-pot coupling reactions between these precursors were performed in the presence of nanosized Cu and PMDETA. The efficiencies of the coupling reactions were greater than 90% determined by the FTIR and ESR spectra. The structure of graft copolymer with 43% of the grafting ratio was confirmed by the spectral analysis. This work provided a route to prepare chitosan graft copolymer.

Synthesis of H‐shaped A3BA3 copolymer by methyl‐2‐nitrosopropane induced single electron transfer nitroxide radical coupling

AbstractAmphiphilic H‐shaped [poly(ethylene oxide)]3‐polystyrene‐[poly(ethylene oxide)]3(PEO3‐PS‐PEO3) copolymer was synthesized by 2‐methyl‐2‐nitrosopropane (MNP) induced single electron transfer nitroxide radical coupling (SETNRC) using PEO3‐(PS‐Br) as a single precursor. First, the A3B star‐shaped precursor PEO3‐(PS‐Br) was synthesized by atom transfer radical polymerization (ATRP) using three‐arm star‐shaped PEO3‐Br as macro‐initiator. Then, in the presence of Cu(I)Br/Me6TREN, the bromide group at PS end was sequentially transferred into carbon‐centered radical by single electron transfer and then nitroxide radical by reacting with MNP in mixed solvents of dimethyl sulfoxide (DMSO)/tetrahydrofuran (THF), and in situ generated nitroxide radical could again capture another carbon‐centered radical by fast SETNRC to form target PEO3‐PS‐PEO3 copolymer. The MNP induced SETNRC could reach to a high efficiency of 90% within 60 min. After the product PEO3‐PS‐PEO3 was cleaved by ascorbic acid, the SEC results showed that there was about 30% fraction of product formed by single electron transfer radical coupling (SETRC) between carbon‐centered radicals. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

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

AbstractA series of ABC triblock copolymers, that is, polyisoprene‐block‐polystyrene‐block‐poly(ethylene oxide) (PI‐PS‐PEO), PI‐block‐poly(tert‐butyl acrylate)‐block‐PEO (PI‐PtBA‐PEO), and PI‐block‐poly(acrylic acide)‐block‐PEO (PI‐PAA‐PEO) were obtained by combination of anionic technique, atom transfer radical polymerization (ATRP), and single electron transfer nitroxide coupling (SETNRC) reaction. Anionic polymerization of isoprene followed by end capping with ethylene oxide yielded hydroxyl‐terminated PI. After esterification, PI with Br end group was used as a macroinitiator to initiate the polymerization of styrene and tBA by ATRP that was then trapped by 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) group in PEO by SETNRC reaction rapidly with high efficiency in tetrahydrofuran at room temperature. The effect of reaction time and polymer chain length on SETNRC reaction was discussed in detail. In the presence of Cu0/tris[2‐(dimethylamino)ethyl]amine, SETNRC between PI‐PS‐Br and PEO‐TEMPO was carried out with the efficiency of up to 91.6% in 2 h. With the increase in polymer chain length, the efficiency decreased fleetly. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Copper(0)‐catalyzed one‐pot synthesis of ABC triblock copolymers via the combination of single electron transfer nitroxide radical coupling reaction and “click” chemistry

AbstractThe synthesis of ABC triblock copolymers were accomplished by Cu(0)‐catalyzed one‐pot strategy combining single electron transfer‐nitroxide radical coupling (SET‐NRC) reaction with “click” chemistry. First, the precursors α,ω‐heterofunctionalized poly(ethylene oxide) (PEO) with a 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) group and an alkyne group, polystyrene (PS), and poly(tert‐butyl acrylate) (PtBA) with bromine or azide end group were designed and synthesized, respectively. Then, the one‐pot coupling reactions between these precursors were carried out in the system of Cu(0)/Me6TREN: The SET‐NRC reaction between bromine group and nitroxide radical group, subsequently click coupling between azide and alkyne group. It was noticeable that Cu(I) generated from Cu(0) by SET mechanism was utilized to catalyze click chemistry. To estimate the effect of Cu(0) on the one‐pot reaction, a comparative analysis was performed in presence of different Cu(0) species. The result showed that Cu(0) with more active surface area could accelerate the one‐pot reaction significantly. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

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.