Search

Amphiphilic 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

The 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

The reductive ring-opening of hydroperoxides derived trom cyclic ketones leads to alkyl radicals which can effectively be trapped by arenediazonium salts. This synthetic transformation yielding azo carboxylic acids or lactams, after a reductive step, can be classified as a radical version of the well-known Beckmann rearrangement. In this article, we present results on the scope, the limitations and possible applications of this new reaction type.

This paper considers the degradation of dimethyl phthalate (DMP), a highly toxic endocrine disrupter, by a novel Fenton reaction involving a new catalyst Si–FeOOH with H 2 O 2 under UV 365 irradiation. Si was selected for its non-toxic and less secondary pollution and the new catalyst Si–FeOOH was synthesized by adding Si to the amorphous FeOOH. The experiment showed that the physical strength of new catalyst Si–FeOOH was enhanced when Si/Fe was 0.2 and the opportunity of dissolved iron was also reduced. The efficiency of DMP degradation by UV/Si–FeOOH/H 2 O 2 could reach 97% after 30 min reaction time at pH 5, 0.5 g/L dosage of Si–FeOOH, and 2.0 mmol/L of H 2 O 2 under 125 W UV 365 irradiation. DMP could be degraded effectively by synergistic effect of UV, Si–FeOOH and H 2 O 2 due to the catalytic absorption and free radicals reaction of FeOOH under the UV irradiation. The Si–FeOOH photocatalyst can be very easily recycled and the efficiency of DMP photodegradation can also remain 87.1% after six runs of DMP degradation.

The effects of zinc dithiocarbamates on degradation and branching of polypropylene (PP) were studied during melt radical modification using a tri-functional monomer (trimethylol propane triacrylate (TMPTA)). High-temperature size-exclusion chromatography (HT-SEC) coupled with differential refractive index detector (DRI), light scattering detector (LSD) and viscometer detector (VD) and rotational rheometry were used to analyse the microstructure of modified PP samples. The chemical structure of the N-substituted group showed an important influence in controlling the evolution of PP microstructure during melt radical reaction. The chain cleavage of PP was controlled in the presence of zinc N, N-dimethyldithiocarbamate (ZDMC), and a substantial long chain branched (LCB) fraction was formed. Without co-agent, the molecular weight of PP decreased measurably, and only a minor LCB fraction was formed. Importantly, considerable amounts of highly branched (microgel and hyperbranched) structures were formed in this case.

Various techniques have been adopted to impart a biological responsiveness to synthetic hydrogels for the delivery of therapeutic agents as well as the study and manipulation of biological processes and tissue development. Such techniques and materials include polyelectrolyte gels that swell and deswell with changes in pH, thermosensitive gels that contract at physiological temperatures, and peptide cross-linked hydrogels that degrade upon peptidolysis by cell-secreted enzymes. Herein we report a unique approach to photochemically deform and degrade disulfide cross-linked hydrogels, mitigating the challenges of light attenuation and low quantum yield, permitting the degradation of hydrogels up to 2 mm thick within 120 s at low light intensities (10 mW/cm(2) at 365 nm). Hydrogels were formed by the oxidation of thiol-functionalized 4-armed poly(ethylene glycol) macromolecules. These disulfide cross-linked hydrogels were then swollen in a lithium acylphosphinate photoinitiator solution. Upon exposure to light, photogenerated radicals initiate multiple fragmentation and disulfide exchange reactions, permitting and promoting photodeformation, photowelding, and photodegradation. This novel, but simple, approach to generate photoadaptable hydrogels portends the study of cellular response to mechanically and topographically dynamic substrates as well as novel encapsulations by the welding of solid substrates. The principles and techniques described herein hold implications for more than hydrogel materials but also for photoadaptable polymers more generally.

Manganese(III)-catalyzed formal [3+2] annnulation of vinyl azides and β-keto acids has been developed for the synthesis of substituted NH pyrroles with a wide range of substituents.

Atom-transfer radical addition (ATRA) reactions of ethyl trichloroacetate, dichloromalononitrile, or diethyl 2,2-dichloromalonate with olefins followed by dechlorination have provided functionalized cyclopropanes in one step. The RuIII complex [Cp*RuCl2(PPh3)] was used as a catalyst precursor and commercial Mn powder as reducing agent. Reactions with the less activated substrate ethyl dichloroacetate gave ATRA products with high turnover numbers but cyclopropanation was not observed.

Azide-alkyne and Diels-Alder click reactions together with a click-like nitroxide radical coupling reaction were used in a one-pot fashion to generate tetrablock quaterpolymer. The various living polymerization generated linear polymers with orthogonal end-functionalities, maleimide-terminated poly(ethylene glycol) (PEG-MI), anthracene- and azide-terminated polystyrene, alkyne- and bromide-terminated poly(tert-butyl acrylate) or alkyne-poly(n-butyl acrylate), and tetramethylpiperidine-1-oxyl (TEMPO)-terminated poly(e-caprolactone) (PCL-TEMPO) were clicked together in a one-pot fashion to generate PEG-b-PS-b-PtBA-b-PCL or PEG-b-PS-b-PnBA-b-PCL quaterpolymer using Cu(0), CuBr, and N,N,N',N",N"-pentamethyldiethylenetriamine as catalyst in dimethyl formamide at 80 °C for 36 h. Linear precursors and target quaterpolymers were analyzed via 1 H NMR and gel permeation chromatography.

This study deals with the synthesis of tert-O-alkyl thiohydroxamates and their use as tert-alkoxyl radical precursors. tert-Alkoxyl radicals were applied in mechanistic studies to determine rate constants of (i) p-chlorocumyloxyl radical addition to bicyclo[2.2.1]heptene (k=1×107 M−1 s−1), (ii) 2-phenylhex-5-en-2-oxyl radical 5-exo-trig-cyclization (kcis=3×109 s−1, ktrans=1×109 s−1), and (iii) 2-methyl-5-phenylpent-2-oxyl to 2-hydroxy-2-methyl-5-phenylpent-5-yl radical isomerization (1,5-H-atom shift; k=0.4–1.5×108 s−1). The reactions pose key steps in synthesis of 2,2,5-substituted tetrahydrofurans and 2-bromo-3-alkoxybicyclo[2.2.1]heptanes. Stereoselectivity in 5-exo-trig cyclization (2,5-cis) and intermolecular addition (exo/endo>99:1), originates from torsional strain in transition structures of alkoxyl radical reactions.

The autoxidation of jet fuel takes place via a complex free radical reaction mechanism that involves the decomposition of hydroperoxides.The liquid-phase, unimolecular decomposition of hydroperoxide has been isolated for experimental study. Three hydroperoxides relevant to jet fuel autoxidation, including cumene hydroperoxide (CHP), dodecane hydroperoxide (DHP), and ethylbenzene hydroperoxide (EBHP), were thermally decomposed separately and found to closely fit first-order behavior with respect to hydroperoxide concentration. The activation energy for liquid-phase thermolysis of these hydroperoxides was found to be significantly less than typical gas-phase values. Parameters affecting the rate of hydroperoxide decomposition, such as dissolved metal content, organic acids, and metal deactivator additive (MDA) were explored. Metal type was shown to be a significant factor affecting hydroperoxide decomposition rate, while naphthenic acids (NA) were shown to have little effect on the rate. However, when disso...

Original way of polyolefin surface activation through covalent grafting of functional polyperoxide (FPP) macromolecules is described. Two interconnected processes, the cross-linking of FPP macromolecules and their grafting to polyolefin surface, govern the peroxidation of polyolefin surface. Ellipsometry, atomic force microscopy (AFM) and contact angle measurements were applied to show that FPP composition and polyolefin reactivity determine the mechanism of peroxidation and properties of grafted polyperoxide films. It is concluded that the grafted fractal (grafted “island”) consists of about 500–1000 cross-linked FPP macromolecules. The latter finding was described by mathematical model characterizing polyperoxide grafting to the polyolefin surface. It was found that thickness of grafted film (20–50 nm) depends on polyperoxide composition and molecular weight. As a result of peroxidation, 0.01–0.03 mmol/m2 peroxide groups can be covalently attached to the polyolefin surface. These groups are further able to initiate radical polymerization on the polyolefin surface.

We report the synthesis of new polyether-based polyols derived from carbohydrates carrying a thioether-spacer in the attempt to potentially provide new antibiotics. The monosaccharide cores are based on d-galactose, d-mannose and d-glucose and the spacer are being built by allylation of the free hydroxyl groups followed by the radical addition of 2-mercaptoethanol using a radical initiator. The CI-MS analysis demonstrated the stepwise and successive fission of the sulfide-spacer groups, however, it did not distinguish between sugars having different arrangement of O-(CH2)3-S(CH2)2OH groups. The SEM image of methyl 2, 3, 4, 6-tetra-O-[3-(hydroxythioethyl)-propyl]-α-d-mannopyranoside, as a representative example, demonstrated a super hydrophobic layer formed via a self-organization effect through the strong hydrogen bonding interactions of the spacer groups. To the best of our knowledge, this is the first report on the formation of such rough surface nanostructure layer from simple monosaccharide. The inves...

Ciguatoxins, the principal causative toxins of ciguatera seafood poisoning, are large ladder-like polycyclic ethers. We report a highly stereoselective 6-exo radical cyclization/ring-closing olefin metathesis sequence to construct the syn/trans-fused polyether system. The new method was applied to the practical synthesis of ciguatoxin CTX3C.

Radical-induced oxidn. of reversible addn.-fragmentation chain transfer (RAFT) agents is studied with respect to the effect of mol. structure on oxidn. rate. The radicals are generated by homolysis of either azobisisobutyronitrile or alkoxyamine and transformed in situ immediately into peroxy radicals through transfer to mol. oxygen. The oxidn. rate depends on the structure of Z- and R-group of thiocarbonylthio compds. For dithioesters with identical Z-Ph substituent, the oxidn. rate decreases in the order of cyanoisopropyl (-C(Me)2CN) > cumyl (-C(Me)2Ph) > phenylethyl (-CH(Me)Ph) > 2-methoxy-1-methyl-2-oxoethyl (-CH(Me) -C(=O)OCH3) > benzyl (-CH2Ph). For dithioesters with identical R-group, the oxidn. rate decreases in the order of Z = phenyl- ∼ benzyl- > RS- (trithiocarbonates) > RO- (xanthates). The stability of the RAFT agents toward oxidn. correlates well with the chain transfer abilities as those previously reported by Rizzardo and coworkers. The priority of the oxidn. reaction over the RAFT process, and the subsequent influence on RAFT polymn. are also studied. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011. [on SciFinder(R)]

Polyethylene (PE), alkoxyamine- and thiol-terminated PEs (PE-TEMPO and PE-SH, respectively) can be converted to macroradicals using a peroxide, a thermal cleavage of the alkoxyamine and a hydrogen transfer reaction of the thiol, respectively. The addition of these macroradicals to multiwalled carbon nanotubes (MWCNTs) were compared by performing grafting reactions at 160 degrees C in 1,3-dichlorobenzene as solvent. Raman spectroscopy was utilized to follow the introduction of PE on the MWCNTs' surface while thermogravimetric and elemental analysis indicated the extent of this grafting. The grafting ratio was found to be in the range of 19-36 wt %. PE-functionalized MWCNTs were imaged by transmission elec-tronic microscopy showing a PE layer with various thicknesses covering the surface of nanotubes. It was found that higher levels of grafting were obtained using PE-2,2,6,6-tetramethyl-piperidinyl-1-oxy and PE-SH rather than a radical grafting reaction in which dicumyl peroxide, PE, and MWCNTs were reacted. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 957-965, 2011

Sonochemical reactors offer excellent promise for the intensification of different chemical processing applications. The current work deals with intensification of cavitational activity using different additives with an objective of decreasing the processing cost as well as enhancing the applicability of sonochemical reactors for different applications. Potassium iodide oxidation has been used as a model reaction. Experiments have been carried out in a laboratory scale ultrasonic horn reactor. The effects of different additives such as air, solid particles (cupric oxide and titanium dioxide), salts (sodium chloride and sodium nitrite) and radical promoters (hydrogen peroxide, ferrous sulphate, iron metal, carbon tetrachloride and t-butanol) on the degradation of potassium iodide have been investigated. Combination of additives has also been investigated for examining the possible synergistic effects in comparison to the use of individual additions. It has been observed that based on the type of additive, optimum concentration needs to be selected and it may not be desirable always to use different additives in combination. It is desirable to select an additive which can give additional reaction mechanism in the system to aid the desired application under question.

An efficient protocol for the synthesis of homopropargylic alcohols using propargylic carbonates as pronucleophiles is reported. The reaction is based on a combination of transition metal (palladium) and radical chemistry (titanium). The reaction takes place with an excellent regioselectivity and tolerates a great degree of substitution of the starting propargylic carbonate, thus being an interesting tool in the context of synthetic organic chemistry.

Free radical addition (UV irradiation, 2―7 h or AIBN, 65―70 °C, 6―7 h) of secondary phosphanes to 1-vinylimidazole, 2-methyl-1-vinylimidazole, and 1-vinylbenzimidazole proceeds regioselectively to give the corresponding anti-Markovnikov adducts in 88―98% yields.

Generation of radicals from B-alkylcatecholboranes represents an efficient tin-free procedure for the generation of alkyl radicals. A modified version of this method has been developed. The simple catechol is replaced by a dihydroxylated tetrahydroisoquinoline, which can be separated from the reaction products by simple extraction with an aqueous acid solution. The modified alkyl radical precursors are easily prepared from alkenes by hydroboration with BH3 center dot Me2S followed by treatment with the dihydroxytetrahydroisoquinoline. The new alkylboronates of this type are suitable radical precursors in a wide range of reactions such as sulfenylation, allylation, alkynylation, vinylation, and addition to quinones. This strategy is particularly useful when separation of reaction products from catechol residues is problematic, as illustrated by a radical addition to 1,4-benzoquinone leading to 2-alkyl-1,4-hydroquinones.

Free-radical degradation of xyloglucan (XG) in aqueous solution initiated by 4,4′-azobis-(4-cyanopentanoic acid), potassium persulfate (KPS), hydrogen peroxide (H 2 O 2 ) and H 2 O 2 with ascorbic acid at 75–80 °C has been investigated using gel permeation chromatography. XG degradation behaviour is similar to that of hydroxyethylcellulose with carbon-centred radicals causing little degradation and oxygen-centred radicals producing significant degradation. Based on the observations, the predominant mode of degradation is believed to be random chain scission of sterically unhindered glycosidic main-chain linkages, with an increasing contribution from side-group scission as the degree of polymerization reduces and the relative concentration of side-group linkages increases. The rate coefficient for random chain scission degradation by KPS at 75 °C was 3.98 × 10 −6 s −1 .

Macrocyclic polystrene (PSt) was produced in high yields by an intramolecular atom transfer radical coupling reaction of the chain ends. The slow addition of the dibrominated polystyrene (BrPStBr) ...

Free radical graft polymerization has been used as a modification method to incorporate functional groups into polyolefins using a melt-mixing process. In this work, modification of polybutene-1 (PB) was performed by limonene radical graft polymerization using the Nd2O3/dicumyl peroxide (DCP) radical initiator system with various mixing ratios in air. The effects of the modification on the crystallization and tensile behavior were studied in detail. The modified PB samples had ketone and limonene groups. The contents of both the ketone and the limonene groups were highest in the modified PB prepared using Nd2O3/DCP (2/0.2 wt%/PB), and a conjugated diene group was found to be produced by a side-reaction. Excess Nd2O3 lowered the limonene graft content in the modified PB. The rate of crystal phase transition (II I) decreased with an increase of limonene content. The presence of a small amount of the ketone group increased the rate, and the modified PB having a small ketone content exhibited more ductility due to its higher crystal phase transition rate. It was found that there was an optimum mixing ratio of the Nd2O3/DCP initiator system for the modification. The ketone and the limonene groups affected the rate of the crystal phase transition and the tensile properties of the modified PB. Copyright © 2010 Society of Chemical Industry

Radical halo-nitration of alkenes using iron(III) nitrate nonahydrate and halogen salt has been developed. The present reaction proceeds by radical addition of nitrogen dioxide generated by thermal decomposition of iron(III) nitrate nonahydrate and subsequent trapping of the resultant radical by a halogen atom in the presence of halogen salt. Application of this method to synthesis of nitroalkenes is also described. The practicality of the present method using nontoxic and inexpensive iron reagents has been shown by the application to broad alkenes.

Sequential intermolecular atom transfer radical addition reactions of activated dichlorides Cl2CRR′ (R = CN, CO2Et, R′ = H, CN, CO2Et) with two olefins catalyzed by [Cp*RuCl2(PPh3)] in the presence Mg allow the synthesis of linear 1,5-dichlorides. Different olefins can be employed in the first and in the second addition reaction. The reaction products are interesting synthetic precursors as demonstrated by the synthesis of two cyclopentanes by Mg-induced dechlorination. The structure of trans-3,4-diphenylcyclopentanecarbonitrile was determined by single-crystal X-ray diffraction.

The effects of the position of a second nitroaromatic group (ortho vs. para vs. meta) during reduction of nitrobenzenes were analysed. Cyclic voltammetric experiments in acetonitrile solution revealed that ortho-, meta- and para-dinitrobenzenes show two reversible reduction processes. An Electrochemical-Electron Spin Resonance (E-ESR) study showed that the corresponding radical anions of the ortho and para derivatives, electrogenerated during the first electron transfer uptake, remain the same even after the second monoelectronic process, increasing their intensity due to the presence of a comproportionation process (A2− + A → 2A −). For the case of the meta derivative, the electrogenerated radical anion at the first reduction peak is consumed at the second reduction step, forming a secondary radical species. During the electrochemical study of methyl 3,5-dinitrobenzoate, two successive and reversible electron processes were also observed; however, in this case, a very rare biradical dianion structure was found. The use of ESR-spectroelectrochemistry shed some light on controversial aspects of nitroaromatic reduction, especially concerning the second and further waves. These results were corroborated and interpreted with quantum chemical calculations of the molecular and electronic structures, electron affinities and spin densities. As a result, electrochemical mechanisms are presented and discussed.

International audience; The radical grafting of pentadecane onto MWCNTs has been investigated. A model for the functionalisation of MWCNTs with molten polyethylene is established, in which a pentadecane radical grafting reaction has been studied in order to determine the reaction conditions necessary to enhance the degree of grafting while minimising side reactions such as radical combination reactions. The effect of a nitroxyle-based radical scavenger (such as TEMPO) on the competition between the recombination of pentadecane radicals and addition to nanotubes has been explored. It was observed that the use of TEMPO resulted in a relatively higher grafting density without excessive pentadecane branching/cross-linking.

Activators generated by electron transfer (AGET) was integrated into atom transfer radical coupling (ATRC) systems to drastically reduce the amount of copper catalyst required to achieve dimerization of monohalogenated polystyrene (PStX) precursors. PStCl or PStBr, prepared by ATRP, were activated and coupled in ATRC systems with varying equivalents of the reducing agent tin(II) ethyl hexanoate (Sn(EH)2) with ligand-bound copper(I) and/or copper(II) present. Effective coupling was only observed in PStBr systems, with total copper content in the reaction mixture able to be reduced into the range of 10–25% of what is typically reported in traditional ATRC reactions of PSt while maintaining coupling yields of >50%. Additional reducing agents, glucose and ascorbic acid, were also studied and were found to be even more effective in some AGET ATRC reactions compared with Sn(EH)2. Best results were achieved with ascorbic acid as the reducing agent (>80% coupled product) with total copper content 25% of what was used for a traditional ATRC. Using an activators regenerated by electron transfer ATRP–AGET ATRC sequence resulted in an overall reduction of total copper down to 0.1–0.25% for the overall reaction sequence (compared with a traditional ATRP–ATRC sequence). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

A new strategy for the one-pot preparation of ABA- type block-graft copolymers via a combination of Cu-catalyzed azide-alkyne cycloaddition (CuAAC) ''click'' chemistry with atom transfer nitroxide radical coupling (ATNRC) reaction was reported. First, sequential ring-opening polymerization of 4-gly- cidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (GTEMPO) and 1- ethoxyethyl glycidyl ether provided a backbone with pendant TEMPO and ethoxyethyl-protected hydroxyl groups, the hydroxyl groups could be recovered by hydrolysis and then esterified with 2-bromoisobutyryl bromide, the bromide groups were converted into azide groups via treatment with NaN3. Subsequently, bromine-containing poly(tert-butyl acrylate) (PtBA-Br) was synthesized by atom transfer radical polymeriza- tion. Alkyne-containing polystyrene (PS-alkyne) was prepared by capping polystyryl-lithium with ethylene oxide and subse- quent modification by propargyl bromide. Finally, the CuAAC and ATNRC reaction proceeded simultaneously between back- bone and PtBA-Br, PS-alkyne. The effects of catalyst systems on one-pot reaction were discussed. The block-graft copolymers and intermediates were characterized by size-exclusion chroma- tography, 1 H NMR, and FT-IR in detail. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 5430-5438, 2010

This review is intended to update the recent developments in the reactivity of methylene- and alkylidenecyclopropanes, covering the literature from 2003 to 2010. The highly strained structure of these atypical compounds allows an otherwise unattainable chemical reactivity in many diverse synthetic applications, such as ring-opening reactions, cycloaddition reactions, rearrangements, radical reactions, polymerisation reactions and miscellaneous reactions including addition reactions with ring conservation and Heck reactions.

The arms of star-like nanogels were replaced by means of dynamic covalent exchange processes, and arm detachment and arm exchange reactions were successfully accomplished. Each star-like nanogel with alkoxyamine units at its branching points consisted of arms of poly(methyl methacrylate) (PMMA) synthesized by atom transfer radical polymerization, and a core of poly(divinylbenzene), synthesized by nitroxide-mediated radical polymerization using functionalized PMMA as a macroinitiator. The alkoxyamine groups were capable of serving as radically exchangeable units. Arm detachment reactions were carried out through a radical crossover reaction by heating the star-like nanogels with an excess of a small molecule alkoxyamine, whereas arm exchange reactions were performed by heating nanogels with higher molecular weight PMMA functionalized with alkoxyamine units at the chain ends. The molecular weights and sizes of the star-like nanogels were examined by gel permeation chromatography–multiangle light scattering and small-angle X-ray scattering measurements, respectively, and the shapes of nanogels were characterized by means of scanning force microscopy. Arm-replaceable star-like nanogels consisting of poly(methyl methacrylate) arms and poly(divinylbenzene) cores with alkoxyamine units at their branching points were synthesized by a combination of atom transfer radical polymerization and nitroxide-mediated radical polymerization. The arms of the star-like nanogels were replaced by means of dynamic covalent exchange processes, and arm detachment and arm exchange reactions were successfully accomplished. The structural changes were confirmed by gel permeation chromatography–multiangle light scattering measurements, small-angle X-ray scattering measurements and scanning force microscopic observation.

Syndiotactic 1,2-polybutadiene nanoparticles (volume average diameter 13 nm) were functionalized in aqueous dispersion by free radical mercaptan addition. By appropriate choice of both water-soluble radical initiator and mercaptan concentration, nanoparticles with a degree of functionalization of up to 85% were prepared using 3-mercaptopropionic acid methyl ester and 3-mercaptopropionic acid. Only a minor portion of double bonds formed cycles instead of the desired thiol−ene addition products. The composition and structure of the nanoparticles were elucidated by combination of elemental analysis, NMR, IR, DLS, and TEM. Highly hydrophilic mercaptans (3-mercaptopropanesulfonic acid sodium salts), in contrast, only reacted with surface accessible double bonds to afford stable and redispersible nanoparticles solely stabilized with covalently bound moieties on their surface. Analogous grafting of the tripeptide glutathione was demonstrated.

The addition of the acetyl radical to benzene, aniline, trifluoromethylbenzene and naphthalene has been investigated using DFT calculations. Addition to benzene is calculated to have an energy barrier of 63.6 kJ mol−1 at the BHandHLYP/6-311G(d,p)+ZPE level of theory. This reaction is associated with simultaneous SOMO→π∗ and π→SOMO interactions with the latter interaction dominating, suggesting that acetyl reacts predominantly as an electrophilic radical in its interaction with benzene. Addition to the ortho and para positions of aniline is calculated to be slightly less favourable, while attack at the meta position is predicted to be unaffected in relation to the chemistry involving benzene. Inclusion of the electron-withdrawing substituent, trifluoromethyl, is predicted to accelerate reactions slightly at the ortho and para positions, while attack at the C1 position of naphthalene is calculated to involve a barrier of 50.3 kJ mol−1 (BHandHLYP/6-311G(d,p)+ZPE).

Polyfluoroalkyl-containing bicyclolactones were synthesized via the sodium dithionite-initiated cycloaddition–lactonization reaction of 2-allyl-4-pentenoic acids and polyfluoroalkyl iodides. The chemo- and stereo-selectivity of the cycloaddition–lactonization reaction strongly depended on the space hindrance of 2-substituent in 2-allyl-4-pentenoic acids. The reaction was believed to proceed through a tandem free radical addition-lactonization process.

Due to the differences in unsaturation levels of constituent rubbers, thioacetate and mercapto functional groups were introduced into hydrogenated natural rubber (HNR) to increase the compatibility of natural rubber (NR)/HNR blends. The effect of thioacetic acid and initiator concentrations including reaction time on the thioacetate content in HNR was investigated. Methanolysis of thioacetate-modified HNR (HNRTA) yielded mercapto-modified HNR (HNRSH). The addition of HNRTA or HNRSH into NR/HNR blends (50/50 wt ratio) increased the tensile strength. The improved mechanical properties of the compatibilized blends were confirmed by scanning electron microscopy, indicating a co-continuous morphology. Furthermore, the susceptibility of the vulcanizates to changes in temperature and ozone were also reported.

The degradation effectiveness and degradation mechanism of representative organophosphorus (OP) pesticide during oxygen plasma treatment have been studied. The identification and quantitative determination of OP pesticide, the degradation mechanisms for OP pesticide destruction, its destruction intermediates, and by-products were performed using gas chromatography/mass spectrometry (GC/MS). Plausible mechanisms of the degradation are discussed. Experimental results indicate that oxygen plasma treatment has noticeable effects on OP pesticide with satisfactory degradation efficiency, which mainly depends on related operating parameters including plasma treatment time, discharge power, distance from the center of the induction coil, and concentrations of OP pesticide. It was found that OP pesticide was degraded into less-toxic compounds, and free radical reaction and addition reaction were to be the dominated the degradation mechanisms for OP pesticides treated by oxygen plasma. Therefore, our results suggest that oxygen plasma is suitable for degradation of OP pesticide.

Forced Open Traditionally, the study of reaction chemistry has relied on random encounters between molecules to initiate the proceedings. Heating and stirring increase the power and frequency of such encounters but provide little finer control. Very recently, chemists have learned how to initiate reactions more directly by embedding precursors in the backbone of a polymer large enough to manipulate with shear forces. Lenhardt et al. (p. 1057 ) applied this technique to a cyclopropyl ring-opening reaction. When the strained triangular carbon rings were embedded within a polymer, shear force applied by sonication ruptured their bonds as the polymer backbone stretched. The taut polymer then redirected the ring-opened intermediates toward a product differently arranged from that generated by simple heating.

A multifunctional initiator 1 with chemically labile disulfide and ester groups bearing four bromoisobutyryl groups was prepared by esterification of bis(2-hydroxyethyl)disulfide with 2,2-bis(2-bro...

Starting from 1H-indole-2-carboxylic acid, a series of spiro[2-oxoindole-pyrrolidines] could be synthesized in a straightforward manner. The key reaction is a Kharasch radical cyclization reaction of trichloroacetylated precursors. The identity of the tricyclic final products that were formed could be determined as spiro[2-oxoindole-pyrrolidines] by using a combination of different analytical techniques ( 1 H NMR, 13 C NMR, gHMBC, HRMS) and additional reactions. The produced skeletons are interesting from a medicinal point of view.

A relatively low-temperature crosslinking method for phenylethynyl (PE) end-capped oligomides was developed. PE end-capped oligomides are typically cured into crosslinked polyimides at 370 � C for about 1 h. The addition of a low vis- cosity mixed-solvent of N-methylpyrrolidinone (NMP)/dimethyl ether of polyethylene glycol (M ¼ 250 g/mol), NMP/DM-PEG- 250, or NMP/polyethylene glycol (M ¼ 400 g/mol), NMP/PEG- 400, as film forming medium for PE-end-capped oligomides was investigated. Fourier transform infrared spectroscopy and 13 C NMR showed that the mixed solvent addition was effective for achieving low-temperature crosslinking of the ethynyl end- caps over the temperature range 200-250 � C. The low tempera

The radical addition to amides derived from chiral 2,5-disubstituted pyrrolidines has been theoretically studied by the use of density functional methods and the results compared with known experimental data. The results agree quite well with those obtained experimentally and allow the full rationalization of the factors influencing the diastereoselectivity. Steric effects are the main factors determining the selectivity, but electronic interactions can also be very important when the attacking alkene is α,β-conjugated, as in acrylic esters or acrylamides. Additions at the α- and β-positions of the amide chain in the auxiliary are subject to different rules, with the former usually yielding high diastereoselectivities both experimentally and theoretically, whereas the latter is theoretically predicted to occur with low selectivity. We fully rationalize these two opposite behaviours and suggest several ways to circumvent this limitation, thus strongly increasing the interest of this type of structure as chiral auxiliaries in radical reactions.

The performance of thiyl radicals RS' in "self-terminating radical cyclisations" was explored. Using the medium-sized cyclodecyne (1) as model system, the reaction of PhS' generated by photolysis of (PhS)2 was used to study the intermolecular S-radical addition and subsequent intramolecular radical translocations. This reaction resulted in the formation of three stereoisomeric sulfides 17a in very good yield, which all possess the bicyclo[4.4.0]decane framework with either cis and trans ring fusion. The isomeric bicyclo[5.3,0]decane framework was not: formed. Product identification was performed using a combination of techniques, e.g. synthesis of authentic samples, X-ray analysis and computational studies of the potential energy surface, which also revealed valuable insight into the mechanism, of this radical cyclisation cascade. The (PhS)2/PhS' system provides an efficient source for in situ generated thiols, which mediate reduction of the α-thio radical, e.g., 13a→17a. The radical cascade initiated by the addition of BnS', tBuS' or AllylS', respectively, to cycloalkyne 1 was typically terminated also by reduction, even in the absence of an apparent H-donor, and resulted in formation of various bicyclic and monocyclic thioethers. The desired "selftermination", e.g., β-fragmentation of the S-R bond in radical intermediate 12/13 and release of a stabilized radical R', was only observed, as minor reaction, pathway in one particular instance where tBuS' was generated by autoxidation of tBuSH. Computional studies showed that the different stereochemical outcome of the radical cyclizations involving S-radicals, compared to O- or N-centred radicals, could be attributed to the reversibility of the initial intermolecular Sradical addition to the C≡C triple bond in cycloalkyne 1. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Novel maleic anhydride (MAH), ethylene glycol oligomer-modified poly(D,L-lactide acid) (PEMLA), and crosslinked-PEMLA were synthesized via a series of chemical bulk modification. Briefly, MAH copolymerized with ethylene oligomer [EGO (including EG, PEG200, PEG400)] to give the PEMA; thereafter, D,L-lactide (DLLA) and prepolymers (PEMA) copolymerized to produce the PEMLA; at last, the crosslinked-PEMLA was synthesized by free radical reaction of the PEMLA. The characterization of PEMLA and crosslinked-PEMLA showed that the introduction of hydrophilic group O and CHCH increased the flexibility and hydrophilicity of PDLLA. Moreover, the degradation of PEMLA and crosslinked-PEMLA were determined by molar weight changes and weight loss rate, and a special method, analysis of degradation positions via 1H-NMR, which indicated that the PEMLA and crosslinked-PEMLA have nice degradation, and the change of content of MAH, EGO can regulate the degradation rate of PDLLA. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

A novel injectable in situ gelling thermosensitive chitosan-block-poly(ethylene glycol) formulation was synthesized for drug delivery applications. Block copolymerization of monomethoxy–poly(ethylene glycol) onto chitosan using potassium persulfate as an initiator was carried under a nitrogen atmosphere in aqueous solution. The effects of potassium persulfate and poly(ethylene glycol) concentrations, reaction time and reaction temperature on block polymerization were studied by determining the yield of reaction (% Y ), polymerization efficiency (% E ) and add-on percentage (%Add-on). Keeping the other conditions constant, the optimum reaction conditions were found to be initiator = 0.01 M, reaction temperature = 60 °C and reaction time = 6 h.

The effect of temperature, catalyst system, and the structure of bromine connected groups on the nitroxide radical coupling (NRC) reaction is investigated in details. A series of polymers with different bromine connected groups as poly (tert-butyl acrylate) (PtBA-Br), polystyrene (PS-Br), and poly (methyl methacrylate) (PMMA-Br) are prepared by atom transfer radical polymerization first, then the bromine-contain- ing polymers were coupled with 2,2,6,6-tetramethylpiperidinyl-1- oxy-containing poly(e-caprolactone) (PCL-TEMPO) in different cat- alyst systems as CuBr/PMDETA, Cu 0 /PMDETA and CuBr/Cu 0 / PMDETA in the temperature range from 90 � Ct o 25 � C. The result shows that the catalyst system of CuBr/Cu 0 /PMDETA is the best one for NRC reaction, in which the NRC reaction could be con- ducted in high efficiency in the wide temperature range from room temperature to high temperature. The efficiency of NRC reaction between PtBA-Br and PCL-TEMPO is more than 85% in the temperature range from 25 to 75 � C, the efficiency between PS-Br and PCL-TEMPO is more than 90% from 25 to 90 � C, and the efficiency between PMMA-Br and PCL-TEMPO is more than 90% only at the room temperature. The effect of bromine connected groups on the NRC reaction is discussed. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2991-2999, 2010

The 2-thiomethylbenzofuran derivatives 3 are conveniently prepared in good yields through the reactions between the readily available 2-methylene-2,3-dihydrobenzofuran-3-ols 1 and the thiol derivatives 2 (including alkyl thiols, thiophenol, and thioacetic acid). The allylic substitution process may be either acid-catalysed or promoted by radical initiators. In the first case, the reactions are carried out at 90 °C in 1,2-dimethoxyethane (DME) as the solvent in the presence of H 2 SO 4 as the proton source. The radical-promoted reactions take place in DME at 90 °C in the presence of azobis(isobutyronitrile) (AIBN) or benzoyl peroxide (BP) as the radical initiator.

Polycarbosilane (PCS) fibers are cured by electron beam irradiation in helium. Then, the cured fibers are pyrolyzed under hydrogen. The mechanisms of carbon removal during pyrolysis are investigated using chemical elemental analysis, FTIR, Raman, and AES analysis. The development of microstructure and phase is examined by SEM, TEM, and XRD. The results show that the thermal cleavage of relatively weak Si–H and Si–CH3 bonds takes place first during pyrolysis in hydrogen, generating free radicals. The free radicals then react with C–H bonds or with each other to form Si–CH2–Si groups, releasing hydrogen and methane. As temperature increases, the Si–CH2–CH2–Si groups in PCS begin to dissociate and react with hydrogen to form methane, resulting in the further removal of carbon and giving silicon-rich silicon carbide fibers (i.e. C/Si

Radical adsorptions and reactions produced in oil hydrocarbon cracking with an asphaltene model molecule were carried out with CATIVIC and MOPAC programs. Density functional theory (DFT) calculations were also performed for comparison. Eley—Rideal (ER) and Langmuir-Hinshelwood (LH) reaction mechanisms, of H•, CH 3 •, and CH 3 CH 2 • radicals with adsorbed H•, were studied on asphaltene unsaturated fragments. Qualitative results indicated that it is possible that radical adsorptions on the asphaltene surface lead to bond activations (surface deformation). The following adsorption energy trend was found for the three different programs: H• > CH 3 • > CH 3 CH 2 •. Approximate reaction energy barriers were evaluated. The ER mechanism has smaller reaction barriers and higher exothermic reactions than the LH mechanism, which means that ER is energetically more feasible than LH. These results indicate that, at low temperatures and high pressure, the asphaltene surface may play an important role in the recombination of free radicals.

In this paper we discuss and interpret the results of shear bond strengths achieved after the use of two silane coupling agents with isocyanato functionality, viz. 3-isocyanatopropyltrimethoxysilane and 3-isocyanatopropyltriethoxysilane. The silanes were used alone and also blended with a non-functional cross-linking silane on silicatized zirconia before light-curing of resin stubs on the surface, as described elsewhere in the first part of our study (see “Part I: Experimental”). A series of reaction mechanisms and conceptual diagrams are also presented. The reaction mechanisms illustrating the effect of adding a cross-linking silane into a silane blend, the silane hydrolysis and the behavior of two organofunctional groups (isocyanate and alkene) of silanes upon reaction with Rely X Unicem Aplicap resin-composite cement are discussed in detail.