In situ generation of nitroxide from alkoxyamines for controlled acrylate polymerization

A general strategy for the controlled nitroxide-mediated polymerization of acrylates from alkoxyamines without addition of excess free nitroxide is outlined. 2,2-Dimethyl-3-(1-phenylethoxy)-4-phenyl-3-azapentane ( 1 ), prepared in one pot by the addition of 1-phenylethyl radicals to 2-methyl-2-nitrosopropane, is heated prior to the addition of monomer to afford a mixture of alkoxyamine 1 , free nitroxide, and 2,3-diphenylbutane. With a 30 min preheating period at temperatures up to 125 °C, the kinetics of the subsequent polymerization of n-butyl acrylate at 125 °C appear largely unaffected, though the ultimate molecular weight of the polymers is dependent upon the preheating temperature. The poly(n-butyl acrylate) samples, that result from this process, have much narrower molecular weight distributions than those which result in the absence of the preheating process. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5128–5136, 2006     

Polyoxazolidones prepared from bisurethans and bisepoxides

Linear polymers containing oxazolidone rings in the main chain were prepared from difunctional urethans and epoxides by the synthetic method previously used for reaction of monofunctional urethans and epoxides. The similarity of the infrared spectra of polymers and model compounds, bisoxazolidones, showed the presence of oxazolidone rings in a polymer chain. The solubility and softening temperatures of the polymers varied with the urethan unit but not with the bisepoxide structure. Polymers prepared from p-phenylenedimethylurethan and variable bisepoxides were insoluble or partially soluble in dimethylformamide, dimethyl sulfoxide, and m-cresol and had higher softening temperatures. Polymers from m-phenylenediethylurethan or toluenediethylurethan and bisepoxides were soluble in the organic solvents mentioned above, and had lower softening temperatures.     

In situ real-time study of crosslinking kinetics in thermal and microwave fields

A comparative investigation has been conducted of the mechanisms and rate of chemical reactions in thermal and microwave fields. A number of nonpolymer-forming and polymer-forming mixtures of different functionality and molecular architecture were prepared and investigated. The advancement of reactions in thermal and microwave fields was monitored in real time by in situ remote near-infrared spectroscopy. The principal finding was that the use of microwaves in lieu of thermal heating had no effect on the mechanism or kinetics during the isothermal cure of various epoxies, polyimides and bismaleimides. No “microwave effect” was observed and it was concluded that the claims of “accelerated kinetics” in the microwave field are unfounded. However, a comparison between thermal and microwave cure assumes a whole new dimension when the temperature distribution inside the sample is considered, and that constitutes a scientifically challenging area that warrants further research. © 1998 John Wiley & Sons, Ltd.     

Polymerization and crosslinking characteristics of a 3-methoxybutyl acrylate

Polymers of 3-methoxybutyl acrylate (3-MBA) were prepared by máss, solution, and emulsion polymerization techniques. The 3-MBA polymers could be converted from soft, rubbery, soluble, thermoplastic films to hard, glossy, flexible, crosslinked films when exposed to air and/or transition metal catalysts at elevated temperatures. The crosslinked polymers are resistant to common organic solvents and to mineral acids. Strong alkalis degraded the crosslinked polymers. The second-order transition temperature of poly-3-MBA is ?56°C. as determined by volume dilatometry. A comparison of the crosslinking properties of poly-3-MBA and other alkyl and alkoxyalkyl polymers is discussed. An autoxidative mechanism is proposed for the crosslinking of 3-MBA polymers.     

In situ crosslinking of polyoxometalate-polymer nanocomposites for robust high-temperature proton exchange membranes

The most practical high-temperature proton exchange membranes (PEMs) are phosphoric acid (PA)-doped polymer electrolytes. However, due to the plasticizing effect of PA, it is a challenge to address the trade-off between the proton conductivity and the mechanical performance of these materials. Here, we report an effective strategy to fabricate robust high-temperature PEMs based on the in situ electrostatic crosslinking of polyoxometalates and polymers. A comb copolymer poly(ether-ether-ketone)-grafted-poly(2-ethyl-2-oxazoline) (PGE) with transformable side chains was synthesized and complexed with H₃PW₁₂O₄₀ (PW) by electrostatic self-assembly, forming PGE/PW nanocomposite membranes with bicontinuous nanostructures. After a subsequent PA-treatment of these membranes, high-temperature PEMs of PGE/PW/PA ternary nanocomposites were obtained, in which the in situ electrostatic crosslinking effect between PW and PGE side chains was generated in the hydrophilic domains of the bicontinuous structures. The microphase separation structure and the electrostatic crosslinking feature endow the PGE/PW/PA membranes with excellent anhydrous proton conductive ability while retaining high mechanical performance. The membranes show a high proton conductivity of 42.5 mS/cm at 150 °C and a high tensile strength of 13 MPa. Our strategy can pave a new route based on electrostatic control to design nanostructured polymer electrolytes.     

In situ formation and reaction of 2-pyridylboronic esters

2-Pyridylboronic esters were generated by cross-coupling 2-bromopyridines with bis(pinacolato)diboron in the presence of a base and palladium catalyst. The boronic esters reacted in situ with unreacted 2-bromopyridines to afford high yields of 2,2′-bipyridines as homocoupled products. Depending upon the reaction conditions, varying amounts of protodeboronated products were also observed. An attempted cross-coupling between two different 2-bromopyridines produced a nearly statistical mixture of homo- and cross-coupled products.     

Dielectric properties of some photo crosslinking acrylate ester copolymers

Photo crosslinking due to the photo polymerization of unsaturated acrylic side-groups attached to copolymers of glycidyl methacrylate and methyl methacrylate (GMA-MMA) by reaction with acrylic acid in the presence of benzoin methyl ether as photolabile initiator has been investigated. The composition of these copolymers based on (GMA-MMA, 30:70) were determined by [¹H] NMR spectroscopy. The reactivity ratios for the GMA-MMA system were determined using the Kelen-Tüdös method.

The dielectric properties of copolymers based on GMA-MMA acrylate ester (30:70) and homopolymers of MMA in combination with different polyfunctional acrylate ester monomers before and after exposure to UV irradiation have been studied in a solid state matrix, over a frequency range of 100 Hz to 50 kHz and at temperatures in the range 20–70°C.     

Synthesis, electropolymerization and electrochemical characterization of some new acrylate substituted thiophene derivatives

In this work, three new acrylate substituted thiophene monomers, (3-thienyl) methylacrylate, 6-(3-thienyl)methoxy-hexylacrylate and 11-(3-thienyl)methoxy-undecylacrylate were synthesized and electropolymerized. Electrochemical polymerisation by a potential step technique leads to the formation of an electroactive film on a Pt electrode in each case. The polymerization involves evidently only the thiophene ring, as no sign of polyacrylate formation could be detected. The oxidation of each polymer was studied by in situ external reflectance FTIR spectroscopy, which showed several bands assigned to (bi)polaron type charge carriers in the region 1500–1000 cm⁻¹. The evolution of the conductivity was studied in situ by the contact electric resistance technique. The conductivity of poly(3-thienyl methacrylate) was found to be higher in aqueous solutions than in acetonitrile. The surface of poly((3-thienyl) methacrylate) was found to have a granular structure observed for many polythiophenes, as studied by atomic force microscopy (AFM).     

In situ formation of chitosan-cyclodextrin nanospheres for drug delivery

Chitosan-cyclodextrin nanospheres were prepared by in situ formation through Michael addition between N-maleated chitosan (NMC) and per-6-thio-β-cyclodextrin sodium salt in an aqueous medium. This facile preparation method did not involve any organic solvent and surfactant. Through adjusting the preparation conditions, the nanospheres with a relatively narrow size distribution could be obtained. The obtained nanospheres were characterized by TEM and particle size analyzer. Doxorubicin hydrochloride (DOX·HCl), a water soluble anticancer drug, was loaded in the nanospheres with a high encapsulation efficiency. The in vitro drug release showed that the release of DOX·HCl from the nanospheres could be effectively sustained. The cytotoxicity evaluation showed the drug loaded nanospheres exhibited efficient inhibition on HeLa cells.     

Synthesis and bio-evaluation of phenothiazine derivatives as new antituberculosis agents

Two series of phenothiazine derivatives were designed and synthesized. All compounds were tested for anti-tuberculosis activities against Mycobacterium tuberculosis H₃₇R_V. In comparison with mother compound of chlorpromazine, compound 6e shows promising anti-tuberculosis activity and much less mammalian cell cytotoxicity, compound 6e merits to be further explored as new anti-tuberculosis agents.     

Palladium-catalyzed synthesis of 3-trifluoromethylated 1,3-dienes from acrylate derivatives and BTP

Here we reported a Pd-catalyzed coupling reaction between acrylate derivatives and BTP (2-bromo-3,3,3-trifluoropropene) to access 3-trifluoromethylated 1,3-dienes. The reaction allows the formation of the corresponding products in good to excellent yields and moderate Z/E diastereoisomeric ratios. This method broadens the current toolbox to access 3-trifluoromethylated 1,3-dienes.     

In situ production of nanocomposites of poly(vinyl alcohol) and cellulose nanofibrils from Gluconacetobacter bacteria: effect of chemical crosslinking

Nanocomposites of poly(vinyl alcohol) (PVA) reinforced with bacterial cellulose (BC) were bioproduced by Gluconacetobacter genus bacteria. BC was grown from a culture medium modified with water-soluble PVA to allow in situ assembly and production of a novel nanocomposite that displayed synergistic property contributions from the individual components. Chemical crosslinking with glyoxal was performed to avoid the loss of PVA matrix during purification steps and to improve the functional properties of composite films. Reinforcement with BC at 0.6, 6 and 14 wt% content yielded nanocomposites with excellent mechanical, thermal and dimensional properties as well as moisture stability. Young’s modulus and strength at break increased markedly with the reinforcing BC: relative to the control sample (in absence of BC), increases of 15, 165 and 680 % were determined for nanocomposites with 0.6, 6 and 14 % BC loading, respectively. The corresponding increase in tensile strengths at yield were 1, 12 and 40 %, respectively. The results indicate an exceptional reinforcing effect by the three-dimensional network structure formed by the BC upon biosynthesis embedded in the PVA matrix and also suggest a large percolation within the matrix. Bonding (mainly hydrogen bonding) and chemical crosslinking between the reinforcing phase and matrix were the main contributions to the properties of the nanocomposite.     

Synthesis of some oxadiazole derivatives as new anticandidal agents

In this study, 5-[(pyrimidin-2-ylthio)methyl]-1,3,4-oxadiazole-2(3H)-thione (3) was synthesized via the ring closure reaction of 2-(pyrimidin-2-ylthio)acetohydrazide (2) with carbon disulphide. New oxadiazole derivatives 4a-f were obtained by the nucleophilic substitution reaction of compound 3 with various phenacyl bromides. The chemical structures of the compounds were elucidated by IR, 1H-NMR, 13C-NMR and FAB+-MS spectral data and elemental analyses. The newly synthesized derivatives 4a-f were tested in vitro by using a microbroth dilution method against C. albicans (clinical isolate, Osmangazi University, Faculty of Medicine, Eski?ehir, Turkey), C. albicans (ATCC 90028), C. glabrata (clinical isolate, Osmangazi University, Faculty of Medicine, Eski?ehir, Turkey), C. tropicalis (NRRL Y-12968), C. krusei (NRRL Y-7179), C. parapsilosis (NRRL Y- 12696), C. albicans (NRRL Y-12983), C. glabrata (clinical isolate, Anadolu University, Faculty of Science, Department of Biology, Eski?ehir, Turkey). Among these compounds, compound 4a was found to be the most potent derivative (MIC = 0.007-0.06 versus ketoconazole: 0.001-0.007 mg/mL) against Candida species, except C. tropicalis and C. krusei when compared with the standard antifungal ketoconazole.     

In situ molecular level visualization of RAFT polymerization by AIEgen-labelled agents

正Can we see clearly the whole polymerization process?Normally, it is difficult and thus is a dream for researchers in polymer science. That is why techniques for monitoring the polymerization process have always been a major focus in both academic and industrial field owing to their potential for quality control and process optimization. Several methods,such as rheometry, viscometry and dilatometry, have been developed to study the kinetics of polymerization process.However, these methodologies examine only the macroscopic viscosity instead of at the molecular level. Online     

Design and synthesis of new imidazolinone derivatives as potential antifungal agents

A new series of chalcones, pyrimidines, and imidazolinone is described; chalcones ( 4a , 4b , 4c , 4d , 4e , 4f , 4g , 4h , 4i , 4j , 4k , 4l , 4m , 4n , 4o ) were prepared from the lead 4‐[2‐(5‐ethylpyridin‐2‐yl)ethoxy]benzaldehyde. Pyrimidines ( 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i , 5j , 5k , 5l , 5m , 5n , 5o ) were prepared from the reaction of chalcones and guanidine nitrate in alkali media. Imidazolinones ( 6a , 6b , 6c , 6d , 6e , 6f , 6g , 6h , 6i , 6j , 6k , 6l , 6m , 6n , 6o ) were synthesized from the reaction of pyrimidine and oxazolone derivatives (prepared by Erlenmeyer azlactone synthesis). The structures of the synthesized compounds were assigned on the basis of elemental analyses, IR, ¹H‐NMR, and ¹³C‐NMR spectral data. All the products were screened against different strains of bacteria and fungi. Most of these compounds showed better inhibitory activity in comparison with the standard drugs. J. Heterocyclic Chem., (2011).     

Synthesis and biological evaluation of new ligustrazine derivatives as anti-tumor agents

To discover new anti-cancer agents with multi-effect and low toxicity, a series of ligustrazine derivatives were synthesized using several effective anti-tumor ingredients of Shiquandabu Wan as starting materials. Our idea was enlightened by the "combination principle" in drug discovery. The ligustrazine derivatives' anti-tumor activities were evaluated on the HCT-8, Bel-7402, BGC-823, A-549 and A2780 human cancer cell lines. In addition the angiogenesis activities were valued by the chick chorioallantoic membrane (CAM) assay. 1,7-bis(4-(3,5,6-Trimethylpyrazin-2-yl)-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (4) and 3 α,12 α-dihydroxy-5β-dholanic acid-3,5,6-trimethylpyrazin-2-methyl ester (5) not only displayed antiproliferative activities on these cancer cells, but also dramatically suppressed normal angiogenesis in CAM. The LD?? value of the compound 5 exceeded 3.0 g/kg by oral administration in mice.     

In vitro antioxidant properties of new thiazole derivatives

A series of novel N2-[2-chloro-4(3,4,5-trimethoxy phenyl azetidin-1-yl]-N4-(substituted aryl)-1,3-thiazole-2,4-diamine (4a–g) were synthesized starting from 3,4,5-trimethoxy benzaldehyde thiosemicarbazone (1). The compound (1) was obtained by condensing 3,4,5-trimethoxy benzaldehyde with thiosemicarbazide in methanol. 3,4,5-Trimethoxy benzaldehyde thiosemicarbazone (1) on treatment with chloracetyl chloride afforded 4-chloro-[2-(3,4,5-trimethoxy benzylidine) hydrazinyl]-1,3-thiazole (2). Compound (2) was reacted with chloracetyl chloride and triethylamine to obtain the corresponding 4-chloro-N-[2-chloro-4(3,4,5-trimethoxy phenyl) azetidin-1-yl]-1,3-thiazole-2-amine (3). Various substitutions on compound 3 with secondary amines yielded series of compounds (4a–g). The newly synthesized compounds were characterized by IR, ¹H NMR, elemental analysis and mass spectral studies. All the compounds were screened for their in vitro antioxidant properties. The IC₅₀ values of compounds 3 and 4a–g revealed that some of the synthesized compounds were showing potent antioxidant activity.     

A new method for in situ crosslinking of stationary phases on fused silica capillary columns

A new mixed crosslinking agent composed of dicumyl peroxide and tetra(methylvinyl)cyclotetrasiloxane was used to prepare fused silica capillary columns with in situ crosslinked stationary phases including PEG-20M, SE-54, and OV-1. These columns proved to have good thermostability and inertness. As examples of potential applications a mixture of isomers of nitrotoluene and dinitrotoluene, and pyrolyzates of polystyrene were separated by using these columns.