Self‐curable polyester by a reaction of glycidol with maleic anhydride

The controlled reaction of equimolar quantities of maleic anhydride and glycidol in dimethoxyethane gives soluble polyesters with one hydroxyl group in each repeating unit. The reaction proceeds with stepwise ring opening of the components and gives highly viscous clear solutions in relatively short periods. In the first step, monomaleate ester formation takes place around 80 °C. The ring opening of the oxirane group is the second step, and it occurs at 120 °C. The overall reaction is the formation of soluble polyesters with moderate molecular weights (6000–18,000), without the elimination of water. The soluble polyesters can be crosslinked tightly by direct heating at 190 °C without additional vinyl monomer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2549–2555, 2003     

Air‐stable and recoverable catalyst for copper‐catalyzed controlled/living radical polymerization of styrene; In situ generation of Cu(I) species via electron transfer reaction

Copper‐catalyzed controlled/living radical polymerization (LRP) of styrene (St) was conducted using the silica gel‐supported CuCl₂/N,N,N′,N′,N″‐pentamethyldiethylenetriamine (SG‐CuCl₂/PMDETA) complex as catalyst at 110 °C in the presence of a definite amount of air. This novel approach is based on in situ generation and regeneration of Cu(I) via electron transfer reaction between phenols and Cu(II). Sodium phenoxide or p‐methoxyphenol was used as a reducing agent of Cu(II) complexes in LRP. The number–average molecular weight, M_n,GPC, increases linearly with monomer conversion and agrees well with the theoretical values up to 85% conversion The molecular weight distribution, M_w/M_n, decreases as the conversion increases and reaches values below 1.2. The catalyst was recovered in aerobic condition and reused in copper‐catalyzed LRP of St. For the second run, the number–average molecular weights increased with monomer conversion and the polydispersities decreased as the polymerization proceeded and reached to the value <1.3 at 81% conversion. The recycled catalyst retained 90% of its original activity in the subsequent polymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 77–87, 2006     

Redox behaviour of cysteine in the presence of ammonium trioxovanadate(V)

The interaction of ammonium trioxovanadate(V) with cysteine in aqueous solution was studied by cyclic voltammetry and absorption spectroscopy techniques. In the absence of cysteine, the cyclic voltammogram (CV) of ammonium trioxovanadate(V) solution in 0.1 M phosphate buffer (pH 7) gave two peaks at -0.130 V (reversible) and -0.400 V (irreversible). These peaks (-0.130 V, -0.400 V) can be attributed to V(V)/V(IV) and V(IV)/V(III) redox processes, respectively. In the presence of cysteine at low scan rate (40 mV/s), the peak at -0.780 V, which is assigned to the irreversible reduction of free cystine, was observed. In addition, the reduction peak of the disulfidic anion S(2)(2-) was seen at -0.650 V. Under aerobic conditions, the peaks of the disulfidic anion S(2)(2-) and free cystine are well separated. From electronic spectra of ammonium trioxovanadate(V) and cysteine mixtures, LMCT transition associated with V(V)-cyteine complex was obtained at 743 nm. The stoichiometry (ML(2)) and stability constant (log beta(1:2)=6.67) of V(V)-cysteine complex were determined by means of mole ratio method.     

Characterization of active sites over reduced Ni-Mo/Al(2)O(3) catalysts for hydrogenation of linear aldehydes

Reduced Ni-Mo/Al(2)O(3) catalysts exhibit a behavior analogous to that of sulfided Ni-Mo/Al(2)O(3) catalysts in hydrogenation of linear aldehydes to alcohols. Similar to what has been previously reported for sulfided catalysts, NO and CO(2) can be used over the reduced Ni-Mo catalysts as probe molecules for the active sites responsible for two competing reactions -- aldehyde hydrogenation to alcohols and condensation reactions to heavy products, respectively. Reduced catalysts have a higher aldehyde conversion activity and alcohol selectivity than their sulfided counterparts. The reduction temperature has a strong effect on the surface density of anion vacancies, which are responsible for alcohol formation. Reduction temperature also plays a role in determining the abundance of OH groups on the alumina surface. The effect of reduction temperature also manifests itself through the differences seen in the oxidation states of Mo and Ni species.     

Development of chromium-free iron-based catalysts for high-temperature water-gas shift reaction

Chromium-free iron-based catalysts were prepared and studied in regard to their performance in the high-temperature water-gas shift reaction (HTS). The effects of various catalyst preparation variables (i.e., Fe/promoter ratio, pH of precipitation medium, calcination and reduction temperatures) and preparation methods were investigated. Aluminum is a potential chromium replacement in HTS catalysts. Further improvement in WGS activity of Fe–Al catalysts can be achieved by the addition of small amounts of copper or cobalt. Catalysts were characterized using BET surface area measurements, temperature-programmed reduction (TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). As a textural promoter, aluminum and chromium prevent the sintering of iron oxides and stabilize magnetite phase by retarding its further reduction to FeO and metallic Fe. The promotional effect of Cu is found to be strongly dependent on the preparation method.     

Suzuki coupling reactions of 2,4,6-trialkoxyphenylboronic acids with enol triflates: asymmetric synthesis of a lactone template for calyxin assemblage

Suzuki coupling reactions between 2,4,6-trialkoxyphenylboronic acids and enol triflates have been found to occur in excellent yield, while the use of an enol tosylate failed to give any of the desired product. This coupling reaction has led to the synthesis of a lactone which could serve as a precursor to several calyxin analogues.     

Visual detection of Al ions using conjugated copolymer-ATP supramolecular complex

A colorimetric Al³⁺ sensor based on fluorescence recovery of a conjugated copolymer-ATP complex is proposed. An optimized ratio of two polythiophene (PT) monomers is utilized to synthesize copolymer (CP) that yielded maximized colorimetric response for Al³⁺ in deionized (DI) and tap water. The electrostatic disassembly of CP-ATP upon addition of Al³⁺ led to an evident visual color change. The lowest concentration of Al³⁺ for naked eye observation is around 4 μM, which is below the threshold levels in drinking water according to European Economic Community (EEC) standard. Besides, the proposed assay showed a similar response to Al³⁺ in tap water. The proposed methodology showed selective and sensitive detection for Al³⁺ in analytically relevant concentration ranges without involving sophisticated instrumentation, illustrating the applicability for on-site drinking water monitoring.     

Polyamide 6‐polycaprolactone multiblock copolymers: Synthesis,characterization, and degradation

This work describes the synthesis and characterization of polyamide 6 (PA 6)‐polycaprolactone (PCL) multiblock copolymers. Low molar mass, fully amine end‐capped PA 6 was prepared by the addition of a diamine monomer during ε‐caprolactam polymerization. A low molar mass PCL was selected to be incorporated as the biodegradable block and was fully end‐capped with toluene 2,4‐diisocyanate. End group analysis and molecular weight characterizations were performed for both end‐functionalized polymers by SEC, NMR and titration analysis. Incorporation of PCL into PA 6 was mainly achieved by solution mixing of the two end‐functional blocks and, was continued after the removal of the solvent with solid state polymerization (SSP) by gradual heating until about 40 °C below the melting temperature of the PA 6. Molecular weights started to grow immediately during solution mixing and only increased marginally during the SSP treatment. FTIR and SEC studies confirmed the reaction between the two components. DSC data, in combination with the enhanced molar mass during solution mixing pointed to a blocky microstructure, for which distinct melting and crystallization temperatures were observed for the PCL and the PA 6 blocks. Hydrolytic and enzymatic degradation studies were performed at 25 °C where the degree of degradation was followed by weight loss analysis, SEM and SEC. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

One‐pot synthesis of star‐block copolymers using double click reactions

3‐Arm star‐block copolymers, (polystyrene‐b‐poly(methyl methacrylate))₃, (PS‐b‐PMMA)₃, and (polystyrene‐b‐poly(ethylene glycol))₃, (PS‐b‐PEG)₃, are prepared using double‐click reactions: Huisgen and Diels–Alder, with a one‐pot technique. PS and PMMA blocks with α‐anthracene‐ω‐azide‐ and α‐maleimide‐end‐groups, respectively, are achieved using suitable initiators in ATRP of styrene and MMA, respectively. However, PEG obtained from a commercial source is reacted with 3‐acetyl‐N‐(2‐hydroxyethyl)‐7‐oxabicyclo[2.2.1]hept‐5‐ene‐2‐carboxamide (7) to give furan‐protected maleimide‐end‐functionalized PEG. Finally, PS/PMMA and PS/PEG blocks are linked efficiently with trialkyne functional linking agent 1,1,1‐tris[4‐(2‐propynyloxy)phenyl]‐ethane 2 in the presence of CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) at 120 °C for 48 h to give two samples of 3‐arm star‐block copolymers. The results of the peak splitting using a Gaussian deconvolution of the obtained GPC traces for (PS‐b‐PMMA)₃ and (PS‐b‐PEG)₃ displayed that the yields of target 3‐arm star‐block copolymers were found to be 88 and 82%, respectively. © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7091–7100, 2008     

Preparation of 3‐arm star polymers (A3) via Diels–Alder click reaction

Diels–Alder click reaction was successfully applied for the preparation of 3‐arm star polymers (A₃) using furan protected maleimide end‐functionalized polymers and trianthracene functional linking agent (2) at reflux temperature of toluene for 48 h. Well‐defined furan protected maleimide end‐functionalized polymers, poly (ethylene glycol), poly(methyl methacrylate), and poly(tert‐butyl acrylate) were obtained by esterification or atom transfer radical polymerization. Obtained star polymers were characterized via NMR and GPC (refractive index and triple detector detection). Splitting of GPC traces of the resulting polymer mixture notably displayed that Diels–Alder click reaction was a versatile and a reliable route for the preparation of A₃ star polymer. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 302–313, 2008