Functionally terminated poly(methyl acrylate) by SET‐LRP initiated with CHBr3 and CHI3

The single‐electron transfer living radical polymerization (SET‐LRP) of methyl acrylate initiated with bromoform (CHBr₃) and iodoform (CHI₃) and catalyzed by Cu(0)/Me₆‐TREN in DMSO at 25 °C provides a reliable method to prepare poly (methyl acrylate) (PMA) with active chain ends and controlled structure that can undergo subsequent functionalization to provide strategies for the synthesis of different block copolymers and other complex architectures. A detailed kinetic and structural analysis was used to assess the scope and the limitations of CHBr₃ and CHI₃ as initiators under SET‐LRP conditions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 278–288, 2008     

Copper‐Mediated Controlled/“Living” Radical Polymerization in Polar Solvents: Insights into Some Relevant Mechanistic Aspects

The field of transition‐metal‐mediated controlled/“living” radical polymerization (CLRP) has become the subject of intense discussion regarding the mechanism of this widely‐used and versatile process. Most mechanistic analyses (atom transfer radical polymerization (ATRP) vs. single‐electron transfer living radical polymerization (SET‐LRP)) have been based on model experiments, which cannot correctly mimic the true reaction conditions. We present, for the first time, a determination of the [Cu^IBr]/[L] (L=nitrogen‐based chelating ligand) ratio and the extent of Cu^IBr/L disproportionation during CLRP of methyl acrylate (MA) in dimethylsulfoxide (DMSO) with Cu⁰ wire as a transition‐metal catalyst source. The results suggest that Cu⁰ acts as a supplemental activator and reducing agent of Cu^IIBr₂/L to Cu^IBr/L. More importantly, the Cu^IBr/L species seem to be responsible for the activation of SET‐LRP.     

Ambient temperature rapid ATRP of methyl acrylate, methyl methacrylate and styrene in polar solvents with mixed transition metal catalyst system

Ambient temperature atom transfer radical polymerization (ATRP) of methyl acrylate (MA), methyl methacrylate (MMA) and styrene (Sty) in the presence of polar solvents (dimethyl sulfoxide: DMSO, dimethylformamide: DMF and acetonitrile: MeCN) with a mixed transition metal catalyst system (Fe(0) as initial activator and CuBr₂/Me₆TREN complex as deactivator) provides a rapid synthesis of polymers with very low polydispersity (PDI) values and predetermined molecular weights. The polymethylacrylate (PMA) prepared using this novel approach contains the Br-terminated chain ends (functionality ∼100%) and can be successfully used for block copolymer synthesis (as demonstrated on the chain extension experiment performed using the PMA–Br macroinitiator). The key elementary reactions involved in this novel ATRP system and some preliminary mechanistic aspects of the process are also discussed.     

Photoelectron spectroscopy of electronic surface structure of the Cs/GaN and Cs/InN interfaces

The electronic structure of the epitaxial GaN, InN nanolayers, and the ultrathin Cs/GaN and Cs/InN interfaces was investigated under ultrahigh vacuum at various Cs coverages. The experiment was carried out using synchrotron-based photoelectron spectroscopy. The photoemission spectra of the valence band and the In 4d, N 2s, Ga 3d, and Cs 4d semicore levels were studied as a function of Cs coverages. It was found that the Cs adsorption in the submonolayer coverage region causes substantial changes in the spectra due to charge transfer between the Cs adlayer and surface Ga or In atoms. The strong interaction of the dangling bonds of Ga or In with Cs adatoms effectively increases the Ga or In valency.     

Calorimetric and spectrophotometric investigation of PLGA nanoparticles and their complex with DNA

The calorimetric investigation of non-coated and chitosan-coated PLGA nanoparticles (NP) shows that at initial temperatures of heating particle swelling takes place what results in an internal architectural change at lower than physiological temperature. It has shown that the temperature of NP tightness perturbing depends on solvent polarity: as more polar is the solvent more stable are particles. The break of existing bonds in NP shell is accompanied with heat absorption peak which undergoes significant changes depending on heating rate. In the wide pH 2–8 interval in transition temperature no changes occurred. The obtained results show that such NP could be used in acidic area for drug transfer, which gives possibility to take medicine orally. It was shown that DNA attaches only to chitosan-coated NP. The optimal ratio for DNA loading onto the NP was found to be 7:1 (W_NP/W_DNA).     

A comparative computational study of the homolytic and heterolytic bond dissociation energies involved in the activation step of ATRP and SET‐LRP of vinyl monomers

A quantum‐chemical calculation of the homolytic and heterolytic bond dissociation energies of the model compounds of the monomer and dimer is reported. These model compounds include the dormant chloride, bromide, and iodide species for representative activated and nonactivated monomers containing electron‐withdrawing groups as well as for a nonactivated monomer containing an electron‐donor group. Two examples of sulfonyl and N‐halide initiators are also reported. The homolytic inner‐sphere electron‐transfer bond dissociation is known as atom transfer and is responsible for the activation step in ATRP. The heterolytic outer sphere single electron transfer bond dissociation is responsible for the activation step in single electron transfer mediated living radical polymerization (SET‐LRP). The results of this study demonstrated much lower bond dissociation energies for the outer sphere single electron transfer processes. These results explain the higher rate constant of activation, the higher apparent rate constant of propagation, and the lower polymerization temperature for both activated and nonactivated monomers containing electron‐withdrawing groups in SET‐LRP. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1607–1618, 2007     

Kinetic simulation of single electron transfer–living radical polymerization of methyl acrylate at 25 °C

A mechanistic comparison of the ATRP and SET‐LRP is presented. Subsequently, simulation of kinetic experiments demonstrated that, in the heterolytic outer‐sphere single‐electron transfer process responsible for the SET‐LRP, the activation of the initiator and of the propagating dormant species is faster than of the homolytic inner‐sphere electron‐transfer process responsible for ATRP. In addition, simulation experiments suggested that in both polymerizations the rate of deactivation is similar. In SET‐LRP, the Cu(II)X₂/L deactivator is created by the disproportionation of Cu(I)X/L inactive species, while in ATRP its concentration is mediated by the bimolecular termination. The combination of higher rate of activation with the creation of deactivator via disproportionation provides, via SET‐LRP, an ultrafast synthesis of polymers with very narrow molecular weight distribution at room temperature. SET‐LRP is mediated by a catalytic amount of Cu(0), and under suitable conditions, bimolecular termination is virtually absent. Kinetic and simulation experiments have also demonstrated that the amount of water available in commercial solvents and monomers is sufficient to induce the disproportionation of Cu(I)X/L into Cu(0) and Cu(II)X₂/L and, subsequently, to change the polymerization mechanism from ATRP to SET‐LRP. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1835–1847, 2007.     

Categorical interpretations of some key agreement protocols

We give interpretations of some known key agreement protocols in the framework of category theory and in this way we propose a method of constructing of many new key agreement protocols.     

Structural Surface Features of Paramagnetic Multifunctional Nanohybrids Based on Silver Oleic Acid

Sols of core–shell silver nanoparticles (AgNPs) are synthesized by electrochemical method. The method provides the ability to adjust the particle size by changing both the concentration of oleic acid and the residence time τ₀ in the organic phase. We synthesized AgNPs with oleic acid (OA) concentration of 0.25% (AgNPs & 0.25% OA) and 0.75% (AgNPs & 0.75% OA). These nanoparticles have been studied using modern physical–chemical methods. Differential thermal analysis curves indicate the chemical nature of bond ligand in the secondary shell; this conclusion is confirmed by quantum chemical simulation and semi-empirical calculation. In the electron paramagnetic resonance spectra of silver-containing sols AgNPs & 0.25% OA and AgNPs & 0.75% OA complex wide asymmetric signals of 500–800 G and g-factor of 2.09–2.13 are recorded, in addition, in the spectra of AgNPs with bilayer the pronounced ferromagnetic contribution is observed. The change of the oleic acid layers of the particles affects the dimension of the nanocrystallites that are being formed and the manifestation of their magnetism.

Trial registration number and date of registration JCS-P-20-03-0188.R1, 22-Sep-2020 (02-Mar-2020)

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