bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel synthesis of biodegradable linear and star block copolymers based on ε‐caprolactone and lactides using potassium‐based catalyst
Authors: Lemmouchi Yahia , Perry Michael C. , Amass Allan J. , Chakraborty Khirud , Schacht Etienne
Published: July 2008

Biodegradable, triblock poly(lactide)‐block‐poly(ε‐caprolactone)‐block‐poly(lactide) (PLA‐b‐PCL‐b‐PLA) copolymers and 3‐star‐(PCL‐b‐PLA) block copolymers were synthesized by ring opening polymerization of lactides in the presence of poly(ε‐caprolactone) diol or 3‐star‐poly(ε‐caprolactone) triol as macroinitiator and potassium hexamethyldisilazide as a catalyst. Polymerizations were carried out in toluene at room temperature to yield monomodal polymers of controlled molecular weight. The chemical structure of the copolymers was investigated by 1H and 13C‐NMR. The formation of block copolymers was confirmed by NMR and DSC investigations. The effects of copolymer composition and molecular structure on the physical properties were investigated by GPC and DSC. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5363–5370, 2008
Synthesis and aggregation of poly(valine)‐poly (ethylene glycol) block copolymers
Authors: Goh Sarah L. , Platt Andrew P. , Rutledge Katherine E. , Lee Iris
Published: July 2008

The solubility nature of many medicines presents a challenge for successful delivery of these drugs to the body. Polymeric carriers are potentially viable as vessels for both the protection and transport of these medicinal substances. In an effort to generate polymeric materials for this desired application, A‐B‐A triblock copolymers have been synthesized with a central block composed of hydrophilic poly (ethylene glycol) (PEG) and flanking hydrophobic sequences composed of five valine units terminated with end groups of varying hydrophobicity. These copolymers were constructed by adding amino acids stepwise to the hydrophilic block using solution phase chemistry. The self‐assembly behavior of all polymers was investigated using fluorimetry with a pyrene probe. In general, copolymers with more hydrophobic end groups exhibited lower critical aggregation concentrations (CACs). Fmoc‐terminated copolymers displayed the lowest CAC of 0.032 mg/mL and demonstrated little cytotoxicity when exposed to SW620 colorectal cancer cells. Transmission electron micrographs show the presence of multiple compartments within these spherical assemblies, which may prove useful in encapsulating medicinal substances. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5381–5389, 2008
Hydroxyl‐terminated hyperbranched aromatic poly(ether‐ester)s: Synthesis, characterization, end‐group modification, and optical properties
Authors: Shanmugam Thiyagarajan , Sivakumar C. , Nasar A. Sultan
Published: July 2008

Novel AB2‐type monomers such as 3,5‐bis(4‐methylolphenoxy)benzoic acid (monomer 1), methyl 3,5‐bis(4‐methylolphenoxy) benzoate (monomer 2), and 3,5‐bis(4‐methylolphenoxy)benzoyl chloride (monomer 3) were synthesized. Solution polymerization and melt self‐polycondensation of these monomers yielded hydroxyl‐terminated hyperbranched aromatic poly(ether‐ester)s. The structure of these polymers was established using FTIR and 1H NMR spectroscopy. The molecular weights (Mw) of the polymers were found to vary from 2.0 × 103 to 1.49 × 104 depending on the polymerization techniques and the experimental conditions used. Suitable model compounds that mimic exactly the dendritic, linear, and terminal units present in the hyperbranched polymer were synthesized for the calculation of degree of branching (DB) and the values ranged from 52 to 93%. The thermal stability of the polymers was evaluated by thermogravimetric analysis, which showed no virtual weight loss up to 200 °C. The inherent viscosities of the polymers in DMF ranged from 0.010 to 0.120 dL/g. End‐group modification of the hyperbranched polymer was carried out with phenyl isocyanate, 4‐(decyloxy)benzoic acid and methyl red dye. The end‐capping groups were found to change the thermal properties of the polymers such as Tg. The optical properties of hyperbranched polymer and the dye‐capped hyperbranched polymer were investigated using ultraviolet‐absorption and fluorescence spectroscopy. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5414–5430, 2008
Palladium‐catalyzed phosphonation of SEBS block copolymer
Authors: Subianto Surya , Choudhury Namita Roy , Dutta Naba K.
Published: July 2008

Phosphonic acid‐bearing styrene–ethylene/butylene–styrene (SEBS) block copolymer was synthesized by bromination and subsequent palladium‐catalyzed phosphonation of SEBS. The phosphonated block copolymer was characterized by spectroscopic, thermal, and conductivity measurements. The new polymer shows good ion‐exchange capacity of ∼0.7 meq/g and proton conductivity of around 2–4 mS/cm (at room temperature and 100% relative humidity) which is in good agreement with literature value of other phosphonated materials. This value was obtained despite a relatively low degree of phosphonation, demonstrating the ability of the phase separated nature of block copolymers to promote proton conductivity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5431–5441, 2008
Synthesis and characterization of bipolar copolymers containing oxadiazole and carbazole pendant groups and their application to electroluminescent devices
Authors: Wang Ping , Chai Chunpeng , Yang Qian , Wang Fuzhi , Shen Zhihao , Guo Haiqing , Chen Xiaofang , Fan Xinghe , Zou Dechun , Zhou Qifeng
Published: July 2008

A series of random copolymers POC10{Poly(2,5‐bis[(5‐decyloxy‐phenyl)‐1,3,4‐oxadiazole]styrene)}‐co‐Poly(N‐vinylcarbazole) (PVK) with different nvk content were synthesized through common radical polymerization and were incorporated into light emitting diodes as emitting layers. The structures and properties of the copolymers were characterized and evaluated by GPC, TGA, DSC, UV, PL, CV, and EL analyses. All the polymers enjoy high thermal stability. Cyclic voltammetry revealed that, with the incorporation of N‐vinylcarbazole to the copolymer, these copolymers had high‐lying HOMO energy values, which facilitated hole injection. PL peaks in the film show blue‐shift compared with those in solutions and fluorescent quantum efficiency decreased with the nvk content increasing, which supported the efficient energy transfer from nvk units to the oxadiazole units. Single‐layer LEDs with the configuration of ITO/PEDOT/PC10‐nvk/Mg:Ag/Ag were fabricated, which emit a blue light around 440 and 490 nm with a maximum brightness of 675.3 cd/m2 and luminous efficiency of 0.108 cd/A. Moreover, we fabricated electrophosphorescent device from bipolar transport copolymer PC10‐nvk4 as host material and an orange‐light‐emitting iridium phosphor IrMDPP as guest. The maximum luminous efficiency of 0.548 cd/A was obtained. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5452–5460, 2008
Kinetic study of copper(I)‐catalyzed click chemistry step‐growth polymerization
Authors: Binauld Sandra , Boisson Fernande , Hamaide Thierry , Pascault Jean‐Pierre , Drockenmuller Eric , Fleury Etienne
Published: July 2008

Oligomers and polymers containing triazole units were synthesized by the copper(I)‐catalyzed 1,3‐dipolar cycloaddition step‐growth polymerization of four difunctional azides and alkynes. In a first part, monofunctional benzyl azide was used as a chain terminator for the polyaddition of 1,6‐diazidohexane and α,ω‐bis(O‐propargyl)diethylene glycol, leading to polytriazole oligomers of controlled average degree of polymerization (DPn = 3–20), to perform kinetic studies on low‐viscosity compounds. The monitoring of the step‐growth click polymerization by 1H NMR at 25, 45, and 60 °C allowed the determination of the activation energy of this click chemistry promoted polyaddition process, that is, Ea = 45 ± 5 kJ/mol. The influence of the catalyst content (0.1–5 mol % of Cu(PPh3)3Br according to azide or alkyne functionalities) was also examined for polymerization kinetics performed at 60 °C. In a second part, four high molar mass polytriazoles were synthesized from stoichiometric combinations of diazide and dialkyne monomers above with p‐xylylene diazide and α,ω‐bis(O‐propargyl)bisphenol A. The resulting polymers were characterized by DSC, TGA, SEC, and 1H NMR. Solubility and thermal properties of the resulting polytriazoles were discussed based on the monomers chemical structure and thermal analyses. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5506–5517, 2008
Side‐chain supramolecular polymers with induced supramolecular chirality through H‐bonding interactions
Authors: Vera Francisco , Almuzara Cristina , Orera Irene , Barberá Joaquín , Oriol Luis , Serrano José Luis , Sierra Teresa
Published: July 2008

Side‐chain supramolecular polymers that show columnar mesomorphism have been prepared through H‐bonding interactions between a polyvinylpyridine polymer as H‐acceptor and different H‐donors derived from benzoic acid. These compounds have been designed according to a promesogenic structure, that is, either disk‐like or banana‐like, to promote stacking and therefore the formation of columnar arrangements. IR studies confirmed the formation of H‐bonds and demonstrated that the H‐bond intensity decreases upon increasing temperature. The mesophase organizations were studied by polarized optical microscopy, differential scanning calorimetry, and X‐ray diffraction. Associations containing poly‐3‐methyl‐4‐vinylpyridine showed supramolecular optical activity, as evidenced by circular dichroism studies on thin films. It is proposed that these supramolecular polymers adopt a helical structure that can be biased toward a given handedness by virtue of the configuration of the stereogenic centers in the peripheral tails of the acids. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5528–5541, 2008
Chemically stable hybrid polymer electrolyte membranes prepared by radiation grafting, sulfonation, and silane‐crosslinking techniques
Authors: Chen Jinhua , Asano Masaharu , Maekawa Yasunari , Yoshida Masaru
Published: July 2008

To prepare a crosslinked hybrid polymer electrolyte membrane (PEM) with high chemical stability, a silane monomer, namely p‐styryltrimethoxysilane (StSi), was first grafted to poly(ethylene‐co‐tetrafluoroethylene) (ETFE) film by γ‐ray preirradiation. Hydrolysis‐condensation and sulfonation were then performed on the StSi‐grafted ETFE (StSi‐g‐ETFE) films to give them crosslinks and proton conductibility, respectively. Thus, a crosslinked proton‐conducting hybrid PEM was obtained. The crosslinks introduced by the silane‐condensation have an inorganic SiOSi structure, which enhance the chemical and thermal stabilities of the PEM. The effect of the timing of the hydrolysis‐condensation (before or after sulfonation) and the sulfonation method (by chlorosulfonic acid or H2SO4) on the properties of the resulting hybrid PEMs such as ion‐exchange capacity, proton conductivity, water uptake, chemical stability, and methanol permeability were investigated to confirm their applicability in fuel cells. We conclude that the properties of the new crosslinked hybrid StSi‐grafted PEMs are superior to divinylbenzene (DVB)‐crosslinked styrene‐grafted membranes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5559–5567, 2008
New aliphatic hyperbranched polyester polyols based on 1,3,5‐tris(2‐hydroxyethyl) cyanuric acid as a core
Authors: Ikladious Nawal E. , Mansour Samia H. , Rozik Nehad N. , Dirnberger Klaus , Eisenbach Claus D.
Published: July 2008

Different generations of new hyperbranched polyester polyols were synthesized by the polycondensation of stoichiometric amounts of the monomer 2,2‐bis (hydroxymethyl) propionic acid (bisMPA) corresponding to each generation with one mole of 1,3,5‐tris(2‐hydroxyethyl) cyanuric acid (THECA) as a trifunctional core. The monomer to core ratio was varied between 3 and 45. The degree of branching (DB) was found to be 0.45 according to the method described by Fréchet and 0.35 according to the definition introduced by Frey et al. and independent of the stoichiometric ratio between core molecule and repeating monomer. The molecular weights, calculated from 1H NMR spectra, increase on going from G1 to G4 and represent 97, 90, 72, and 58% from their theoretical molar masses, respectively. In view of the obtained results, it may be argued that the higher generations of the hyperbranched polyesters possess actually lower molecular weights and hydroxyl functionality than their theoretical ones due to some side reactions, e.g., cyclization and or self‐condensation of bisMPA that occurred during the synthesis. The thermal stability and glass transition temperatures of the hydroxyl‐terminated hyperbranched polyesters were determined. Two hyperbranched urethane methacrylates were synthesized by modifying 100 and 50% of the hydroxyl groups of G1 and G3, respectively. Their molecular structures were identified using IR and 1H NMR spectroscopy, and their thermal properties were also investigated. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5568–5579, 2008
An X‐shaped π‐conjugated polymer comprising of fluorene units and anthracene units with high efficiency. Synthesis and optical and electrochemical properties
Authors: Sun Jing , Cheng Jian‐Gong , Zhu Wen‐Qing , Ren Shi‐Jie , Zhong Hong‐Liang , Zeng Dan‐Li , Du Jun‐Ping , Xu Er‐Jian , Liu Ying‐Chun , Fang Qiang
Published: July 2008

A new X‐shaped π‐conjugated monomer comprising of fluorene units and anthracene units was synthesized, and it was used to fabricate the new X‐shaped π‐conjugated polymers and investigate the properties of the new polymers. Using different molar ratios between such monomer and a fluorene monomer gave three polymers that showed higher absolute PL quantum yields than the linear polyfluorene (PF) in the solid state. After thermal annealing at 200 °C for 4 h, the linear PF showed an additional bathochromic emission at about 550 nm, whereas such red‐shifted emission was fully eliminated for the X‐shaped polymers. The electroluminescent devices based on the X‐shaped polymers with a configuration of ITO/PEDOT:PSS/polymer/LiF/Ca/Al displayed blue emission with low turn‐on voltage and high brightness. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5616–5625, 2008
A novel azo‐containing dithiocarbamate used for living radical polymerization of methyl acrylate and styrene
Authors: Xue Xiaoqiang , Zhang Wei , Cheng Zhenping , Zhu Jian , Zhu Xiulin
Published: July 2008

A novel azo‐containing dithiocarbamate, 1‐phenylethyl N,N‐(4‐phenylazo) phenylphenyldithiocarbamate (PPADC), was successfully synthesized and used to mediate the polymerization of methyl acrylate (MA) and styrene (St). In the presence of PPADC, the reversible addition‐fragmentation chain transfer (RAFT) polymerization was well controlled in the case of MA, however, the slightly ill‐controlled in the case of St. Interestingly, the polymerization of St could be well‐controlled when using PPADC as the initiator in the presence of CuBr/PMDETA via atom transfer radical polymerization (ATRP) technique. In the cases of RAFT polymerization of MA and ATRP of St, the kinetic plots were both of first‐order, and the molecular weight of the polymer increased linearly with the monomer conversion while keeping the relatively narrow molecular weight distribution (Mw/Mn). The molecular weight of the polymer measured by gel permeation chromatographer (GPC) was also close to the theoretical value (Mn(th)). The obtained polymer was characterized by 1H‐NMR analysis, ultraviolet absorption, FTIR spectra analysis and chain‐extension experiments. Furthermore, the photoresponsive behaviors of azobenzene‐terminated poly(methyl acrylate) (PMA) and polystyrene (PS) were similar to PPADC. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5626–5637, 2008
Synthesis of azobenzene‐containing polymers via RAFT polymerization and investigation on intense fluorescence from aggregates of azobenzene‐containing amphiphilic diblock copolymers
Authors: Xu Jie , Zhang Wei , Zhou Nianchen , Zhu Jian , Cheng Zhenping , Xu Yan , Zhu Xiulin
Published: July 2008

The well‐defined azobenzene‐containing homopolymers, poly{6‐(4‐phenylazophenoxy)hexyl methacrylate (AHMA)} (PAHMA), were synthesized via reversible addition fragmentation chain transfer polymerization (RAFT) in anisole solution using 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN) as the RAFT agent and 2,2′‐azobisisobutyronitrile (AIBN) as the initiator. The first‐order kinetic plot of the polymerization and the linear dependence of molecular weights of the homopolymers with the relatively low polydispersity index values (PDIs ≤ 1.25) on the monomer conversions were observed. Furthermore, the amphiphilic diblock copolymer, poly{6‐(4‐phenylazophenoxy)hexyl methacrylate (AHMA)}‐b‐poly{2‐(dimethylamino)ethyl methacrylate (DMAEMA)} (PAHMA‐b‐PDMAEMA), was prepared with the obtained PAHMA as the macro‐RAFT agent. The structures and properties of the polymers were characterized by 1H NMR and GPC, respectively. Interestingly, the amphiphilic diblock copolymers in chloroform (CHCl3) solution (PAHMA23‐b‐PDMAEMA97 (4 × 10−5 M, Mn(GPC) = 18,400 g/mol, PDI = 1.48) and PAHMA28‐b‐PDMAEMA117 (6 × 10−5 M, Mn(GPC) = 19,300 g/mol, PDI = 1.51) exhibited the intense fluorescence emission at ambient temperature. Moreover, the fluorescent intensity of PAHMA‐b‐PDMAEMA in CHCl3 was sensitive to the ultraviolet irradiation at 365 nm, which increased within the first 10 min and later decreased when irradiation time was prolonged to 30 min or longer. The well distributed, self‐assembled micelles composed of azobenzene‐containing amphiphilic diblock copolymers, (PAHMA‐b‐QPDMAEMA)s (QPDMAEMA is quaternized PDMAEMA), in the mixed N,N‐dimethyl formamide (DMF)/H2O solutions were prepared. Their fluorescent intensities decreased with the increasing amount of water. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5652–5662, 2008
Implications of monomer and initiator structure on the dissociative electron‐transfer step of SET‐LRP
Authors: Rosen Brad M. , Percec Virgil
Published: July 2008

The heterolytic dissociation process associated with the activation of Single Electron‐Transfer Living Radical Polymerization is examined through the use of energy profile modeling. Monomer and initiator structure is correlated with the approximate activation barriers, energies of electrostatic ion‐radical pair formation, and stability of ion‐radical pair generated from the counteranion halide leaving group and the radical atom with partial positive charge density induced by its electron‐withdrawing substituent. Energy profiles permit access not just to one, but to all local minima, in the dissociation pathway and the identification of a global minimum. The location and energy of this global minimum allows for the placement of various initiators and dormant propagating macroradicals on the spectrum between stepwise and concerted dissociative electron‐transfer. The barrier for the activation step for alkyl‐halides derived from acrylates, vinyl halides, and styrenes, as well as from initiators bearing electron‐withdrawing groups is decreased in comparison to relatively more electron‐rich alkyl halides. This rate enhancement is explained through the sticky dissociative model wherein electron‐transfer is accelerated by the formation of strong ion‐radical pairs between radicals with partial positive charge density and their counteranion leaving group. Greater electron‐withdrawing capacity of the alkyl halide substituent increases the stability of the ion‐radical pair, reduces its equilibrium bond length, and accelerates electron‐transfer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5663–5697, 2008
Chemistry of olefin polymerization reactions with chromium‐based catalysts
Authors: Kissin Yury V. , Brandolini Anita J.
Published: July 2008

Detailed GC analysis of oligomers formed in ethylene homopolymerization reactions, ethylene/1‐hexene copolymerization reactions, and homo‐oligomerization reactions of 1‐hexene and 1‐octene in the presence of a chromium oxide and an organochromium catalyst is carried out. A combination of these data with the analysis of 13C NMR and IR spectra of the respective high molecular weight polymerization products indicates that the standard olefin polymerization mechanism, according to which the starting chain end of each polymer molecule is saturated and the terminal chain end is a CC bond (in the absence of hydrogen in the polymerization reactions), is also applicable to olefin polymerization reactions with both types of chromium‐based catalysts. The mechanism of active center formation and polymerization is proposed for the reactions. Two additional features of the polymerization reactions, co‐trimerization of olefins over chromium oxide catalysts and formation of methyl branches in polyethylene chains in the presence of organochromium catalysts, also find confirmation in the GC analysis. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5330–5347, 2008
Foaming behavior of polypropylene/polystyrene blends enhanced by improved interfacial compatibility
Authors: Zhai Wentao , Wang Hongying , Yu Jian , Dong Jinyong , He Jiasong
Published: July 2008

A series of polypropylene (PP)/polystyrene (PS) blends were prepared by solvent blending with PS‐grafted PP copolymers (PP‐g‐PS) having different PS graft chain length as compatibilizers. The interfacial compatibility was significantly improved with increasing PS graft chain length until the interface was saturated at PS graft chain length being 3.29 × 103 g/mol. The blends were foamed by using pressure‐quenching process and supercritical CO2 as the blowing agent. The cell preferentially formed at compatibilized interface because of low energy barrier for nucleation. Combining with the increased interfacial area, the compatibilized interface lead to the foams with increased cell density compared to the uncompatibilized one. The increase in interfacial compatibility also decreased the escape of gas, held more gas for cell growth, and facilitated the increase in expansion ratio of PP/PS blend foams. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1641–1651, 2008
Effect of diphenylsiloxane unit content on relaxation behavior of poly(dimethylsiloxane‐co‐diphenylsiloxane)
Authors: Qu Liangliang , Xie Zhijian , Huang Guangsu , Tang Zhenhua
Published: July 2008

The relaxation behaviors of poly(dimethylsiloxane‐co‐diphenylsiloxane)s with different compositions were investigated using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). It is indicated that the content of Ph2SiO unit, which is closely associated with crystallinity of polysiloxane, has a remarkable influence on its relaxation behavior. Two‐phase (crystalline and amorphous phase) structure in the semicrystalline polysiloxane of the present system can be determined for discussing relaxation behavior. An increase in relaxation strength can be reasoned to a cooperative effect of decrease in fraction of crystalline phase and increase in friction between molecular chains. And enhancements in glass transition temperature (Tg) and effective activation energy for glass transition (Ea(eff)) were ascribed more to the stiffness imposed by Ph2SiO unit than decrease in fraction of crystalline phase. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1652–1659, 2008
Thermorheological properties of LLDPE/LDPE blends: Effects of production technology of LLDPE
Authors: Delgadillo‐Velázquez O. , Hatzikiriakos S. G. , Sentmanat M.
Published: July 2008

The thermorheological behavior of a number of LLDPE/LDPE blends was studied with emphasis on the effects of the production technology of the linear low‐density polyethylene (LLDPE) and the effects of long chain branching (LCB). Two Ziegler‐Natta LLDPE's (LL3001.32 and Dowlex2045G) and two metallocene LLDPEs (AffinityPL1840 and Exact 3128) were blended with a single low‐density polyethylene (LDPE), with all LLDPEs having distinctly different molecular weight. The weight fractions of the LDPEs used in the blends were 1, 5, 10, 20, 50, and 75%. DSC analysis has shown that the blends with metallocence LLDPEs are miscible in the crystal state, whereas for the Ziegler‐Natta, apart from the two distinct peaks of the individual components, a third peak appears which indicates the existence of a third phase that is created from the cocrystallization of components from the two blended polymers. The linear viscoelastic characterization was performed and mastercurves at 150 °C were constructed for all blends to check miscibility using the time temperature superposition principle. In addition, Van Gurp Palmen and zero‐shear viscosity versus composition were constructed to check the thermorheological behavior of all blends. In general, good agreement is found among these various methods. It was concluded that metallocene LLDPEs are more compatible with LDPE at all LDPE compositions when compared with their Ziegler‐Natta counterparts. Finally, the extensional properties of all blends were studied to examine the effects of different levels of LCB on their extensional rheological properties. It was concluded that extensional rheology is a sensitive tool capable of detecting subtle changes in the polyethylene macrostructure, that is, low levels of LCB. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1669–1683, 2008
Improving the dispersion and interfaces in polymer‐carbon nanotube nanocomposites by sample preparation choice
Authors: Lee Chang‐Uk , Dadmun Mark D.
Published: July 2008

Polymer nanocomposites composed of poly(styrene‐ran‐vinyl phenol) (PSVPh) copolymers and 5 wt % multi‐walled carbon nanotubes (MWNTs) were prepared by three different methods, including melt‐mixing and precipitation. The MWNTs were either oxidized to incorporate oxygenated defects or utilized as received. The mechanical properties of the nanocomposites were measured by dynamic mechanical analysis (DMA), and the extent of intermolecular hydrogen bonding between MWNTs and PSVPh was quantified by infrared (IR). Our DMA results suggest that melt‐mixing leads to more stable morphologies of the final nanocomposites than precipitation. Additionally, the IR analysis of the nanocomposites indicates melt‐mixing can result in the formation of more intermolecular hydrogen bonding between the MWNTs and PSVPh than precipitation, and thus suggests that melt‐mixing leads to more reproducible mechanical properties than precipitation. Our DMA and IR results may provide guidelines to realize the desired morphologies and to improve the properties of polymer carbon nanotube nanocomposites by optimizing intermolecular interactions between MWNTs and polymers using processing. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1747–1759, 2008
Generation and Transportation Mechanisms of Chemically Active Species by Dielectric Barrier Discharge in a Tube for Catheter Sterilization
Authors: Sato Takehiko , Furuya Osamu , Ikeda Kei , Nakatani Tatsuyuki
Published: July 2008

The mechanisms of generation and transportation of a chemically active species in a tube generated by dielectric barrier discharge have been analyzed by experimental and computational methods to elucidate the sterilization mechanism. The obtained results are: i) Nitrogen oxide is an important sterilization factor. ii) Two‐dimensional profiles of emission intensities that expand between the wire and ground in a cross section of the tube were generated by streamer propagation and relaxation processes. iii) A twin vortex was induced in the cross section of the tube by the discharge. Chemically active species, probably transported from the discharge region to the upper region of the tube by the twin vortex, were concentrated by the circular flow.

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Application of Nitramines Coated with Nitrocellulose in Minimum Signature Isocyanate‐Cured Propellants
Authors: Zhang Wei , Fan Xuezhong , Wei Hongjian , Li Jizhen
Published: July 2008

Cyclotrimethylenetrinitramine (RDX) coated with nitrocellulose (NC‐RDX) is prepared by an internal solution method and applied in a minimum signature isocyanate‐cured propellant. It was found that RDX was coated or bonded by NC to form NC‐RDX particles; the median particle diameter (d50) and specific surface area of NC‐RDX are in the range from 150 to 240 μm and 0.03 to 0.04 m2⋅g−1, respectively. The NC‐RDX particles could swell in nitrate ester plasticizers with relatively low swelling rate compared with NC added directly in the plasticizers. Different types of ballistic modifiers can be effectively added to NC‐RDX. It was experimentally shown that NC‐RDX can increase the content of NC in the propellant with viscosities in the range from 371 to 394 Pa s and improve the mechanical characteristics of the propellant with maximum tensile strength (σm) between 0.48 MPa<σm<1.92 MPa, elongation at maximum tensile strength (εm) between 28.0%<εm<37.3%, and elastic modulus between 3.18 MPa<E<8.68 MPa in the temperature range from −40 to +50 °C.
Bias voltage dependence of magnetic tunnel junctions comprising amorphous ferromagnetic CoFeSiB layer with double barriers
Authors: Yim H. I. , Lee S. Y. , Hwang J. Y. , Rhee J. R. , Chun B. S. , Wang K. L. , Kim Y. K. , Kim T. W. , Lee S. S. , Hwang D. G.
Published: July 2008

Double‐barrier magnetic tunnel junctions (DMTJs) with and without an amorphous ferromagnetic material such as CoFeSiB 10, CoFe 5/CoFeSiB 5, and CoFe 10 (nm) were prepared and compared to investigate the bias voltage dependence of the tunneling magnetoresistance (TMR) ratio. Typical DMTJ structures were Ta 45/Ru 9.5/IrMn 10/CoFe 7/AlOx /free layer 10/AlOx /CoFe 7/IrMn 10/Ru 60 (in nanometers). The interlayer coupling field and the normalized TMR ratios at the applied voltages of +0.4 and –0.4 V of the amorphous CoFeSiB free‐layer DMTJ offer lower and higher values than that of the polycrystalline CoFe free‐layer DMTJ, respectively. An amorphous ferromagnetic CoFeSiB layer improves the interface roughness of the free layer/tunnel barrier and, as a result, the interlayer coupling field and bias voltage dependence of the TMR ratio are suppressed at a given voltage. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fabrication and transport properties of 12CaO·7Al2O3 (C12A7) electride nanowire
Authors: Nishio Y. , Nomura K. , Miyakawa M. , Hayashi K. , Yanagi H. , Kamiya T. , Hirano M. , Hosono H.
Published: July 2008

Electron‐doped 12CaO·7Al2O3 (C12A7) nanowires (NWs) were fabricated by two approaches. First, spatially selective electron doping of C12A7 films was examined by using a chemical method specific to C12A7. However, the conductive NW was not formed due to diffusion of oxygen in the C12A7 films to the conductive area. Secondly, a combination of dry etching and electron doping was examined. NWs with conductivities ∼6 S/cm at 300 K were successfully fabricated by this method. The temperature dependence of the conductivity in the NWs exhibited almost degenerated conduction down to 5 K. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Relationship between non‐localized tail states and carrier transport in amorphous oxide semiconductor, In–Ga–Zn–O
Authors: Nomura K. , Kamiya T. , Ohta H. , Shimizu K. , Hirano M. , Hosono H.
Published: July 2008

The relationship between non‐localized tail states and carrier transport in transparent amorphous oxide semiconductor, In–Ga–Zn–O (a‐IGZO), was investigated. It was found that the energy width (E0) of the non‐localized tail states varied from <7 meV to 20 meV depending on the film deposition conditions (i.e. film quality). At carrier concentrations of ∼1019 cm–3, Hall mobilities larger than 10 cm2 (V s)–1 were obtained for the high‐quality films, while they were only several cm2 (V s)–1 for low‐quality films that have large E0 values ∼20 meV. However, even for low‐quality films, the E0 value decreased from 20 meV to 7 meV and their Hall mobilities were increased from ∼1 cm2 to >10 cm2 (V s)–1 by post thermal annealing at ≥300 °C. These observations indicate that structural relaxation associated with electron transport starts from ∼300 °C, which is much lower than the crystallization temperature (∼520 °C). This situation is similar to the case of amorphous metals. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical modelling of aluminium vapour produced by nanosecond UV laser beam ablation
Authors: Hamadi F. , Amara E. H. , Kerdja T. , Mezaoui D.
Published: July 2008

In the present paper, we propose a numerical modelling of the plasma or vapour expansion into target chamber, produced by nanosecond UV laser beam on an aluminium sample surface. The vaporised material ejected is composed of neutrals, metallic ion species and electrons, which are modelled as an ideal gas. The vapour temperature, velocity contours, surface temperature distribution in the target, and the effect of a background pressure gas on the expansion of the plasma plume are calculated using the computational fluid dynamics software “Fluent”, based on a finite volume discretization. The dynamical state of the plasma species is described by the compressible Navier‐Stokes conservation equations for mass, and momentum, and energy conservation equation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Excimer laser annealing of microcrystalline silicon
Authors: Pier T. , Kandoussi K. , Simon C. , Coulon N. , Mohammed‐Brahim T. , Lhermite H.
Published: July 2008

The development of flexible displays and screens is now a major target of the industry. This purpose requires the elaboration of pliant substrate compatible processes. The main obstacle is the vulnerability of such substrates toward heat. Most parts of usual processes are able to be performed at low temperature, but polycrystalline silicon deposition always involves high temperature. Polycrystalline silicon is necessary to reach high mobility, which, in the case of flexible screens, is critical to decrease the area of the pixel circuit and then to reach high aperture ratio. One solution consists in low temperature deposition of microcrystalline silicon followed by an excimer laser crystallization phase. Microcrystalline silicon films were deposited at low temperature (165 °C maximum) by radio‐frequency plasma enhanced chemical vapour deposition on glass substrate covered with silicon dioxide film and on polyethylene naphtalate covered with silicon dioxide film as flexible substrate. These microcrystalline silicon films were excimer laser crystallized, using a step‐by‐step method. Polyethylene naphtalate substrates underwent crystallization without showing any damage. Using deposits made on glass, the crystallization technique has been optimised to obtain the highest crystalline quality starting from 200 nm thick microcrystalline silicon films. On each kind of substrate, crystallized films were characterized using Raman spectroscopy, scanning electron microscopy and atomic force microscopy. Raman spectrum shows very sharp transverse optic peak at 521 cm–1. The small full width at half maximum, 4 cm–1, is close to the value for single crystalline silicon. Scanning electron microscopy and atomic force microscopy reveal silicon grains with size over 400 nm on glass and 100 nm on polyethylene naphtalate. Thin film transistors with a mobility of 400 cm²/V.s on glass and 46 cm²/V.s on polyethylene naphtalate have been produced from such crystallized layers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of spirostanol saponins in Solanum torvum by high‐performance liquid chromatography/evaporative light scattering detector/electrospray ionization with multi‐stage tandem mass spectrometry
Authors: Lu Yuanyuan , Luo Jianguang , Xu Deran , Huang Xuefeng , Kong Lingyi
Published: July 2008

High‐performance liquid chromatography with an evaporative light scattering detector and electrospray ionization multistage tandem mass spectrometry (HPLC/ELSD/ESI‐MSn) was used to identify spirostanol saponins in a saponin extract of Solanum torvum. The fragmentation behavior of saponins was studied using ESI‐MS1–3 in positive ion mode. The MSn spectra of the [M+H]+ ions provide structural information including aglycone type and the nature and sequence of sugars. The use of ELSD allowed the profiling of the nonchromophore‐containing saponins in this plant. The MS analysis established in this study with known saponins was successfully applied to tentatively identify two new siprostanol glycosides, neosolaspigenin 6‐O‐β‐D‐quinovopyranoside and solagenin 6‐O‐[β‐D‐xylopyranosyl‐(1 → 3)‐O‐β‐D‐quinovopyranoside]. Copyright © 2008 John Wiley & Sons, Ltd.
Measurement of sugars using the laser spray technique with a gold capillary
Authors: Takamizawa Atsushi , Maeda Hiroaki , Kambara Shizuka , Furuya Hiroko , Hiraoka Kenzo
Published: July 2008

A gold (Au) capillary has higher thermal conductivity than a stainless steel capillary and can withstand capillary over‐heating induced by high CO2 laser irradiation (over 2.5 W) better than a stainless steel capillary. For this study, a laser spray using an Au capillary was applied for the detection of sugars. The signal of cationized compounds [M+Na]+ can be detected with higher sensitivity than with conventional laser sprays using high laser power (over 2.7 W). Using 3.5 W of laser power, the signal intensity is 15 times higher than the maximum value with stainless steel (2.3 W) in a 10−5 M maltose aqueous solution. It is considered that almost all the water molecules evaporate by laser irradiation, which is impossible to achieve using a stainless steel capillary. Copyright © 2008 John Wiley & Sons, Ltd.
The simple random walk and max‐degree walk on a directed graph
Authors: Montenegro Ravi
Published: July 2008

We bound total variation and L∞ mixing times, spectral gap and magnitudes of the complex valued eigenvalues of general (nonreversible nonlazy) Markov chains with a minor expansion property. The resulting bounds for the (nonlazy) simple and max‐degree walks on a (directed) graph are of the optimal order. It follows that, within a factor of two or four, the worst case of each of these mixing time and eigenvalue quantities is a walk on a cycle with clockwise drift. © 2008 Wiley Periodicals, Inc. Random Struct. Alg., 2009
Levoatrial cardinal vein in mitral atresia and closed foramen ovale: prenatal diagnosis and perinatal management
Authors: Tutschek B. , Schmidt K. G.
Published: July 2008

A levoatrial cardinal vein is a rare cardiovascular anomaly that may be present in malformed hearts with severe left heart obstruction and restrictive interatrial communication. We report the prenatal diagnosis at 23 weeks of a fetus with mitral atresia, double‐outlet right ventricle, premature closure of the foramen ovale and a levoatrial cardinal vein draining into the innominate vein. In a prior examination performed elsewhere the levoatrial cardinal vein had been interpreted as an aortic arch perfused retrogradely, and hypoplastic left heart syndrome with aortic atresia had been diagnosed. Prenatal management, induction at 38 weeks and postnatal examinations and treatment are reported. To the best of our knowledge, this is the first reported prenatal diagnosis of this embryological vessel, presenting a potential pitfall for prenatal echocardiography. Copyright © 2008 ISUOG. Published by John Wiley & Sons, Ltd.
Internal fixation of proximal humeral fractures with locking proximal humeral plate (LPHP) in elderly patients with osteoporosis
Authors: Siwach Ramchander , Singh Roop , Rohilla Rajesh Kumar , Kadian Virender Singh , Sangwan Sukhbir Singh , Dhanda Manjeet
Published: July 2008

Background

Different operative techniques used for treating displaced proximal humeral fractures could result in malunion, non-union, osteonecrosis of humeral head, loosening of screw and loss of reduction particularly in comminuted and osteoporotic fractures. Locking compression plate (LPHP) has been proposed for open reduction and internal fixation of these fractures and is associated with less complication rate.

Materials and methods

We prospectively assessed the functional outcome and the complications after an average follow-up of 24.9 months in 25 patients of proximal humeral fractures with osteoporosis. Mean age was 62 years. Using AO classification, 48% were type A and 52% type B.

Results

Mean constant score was 80 points. According to constant score, 28% had excellent outcome, 64% had good functional outcome, and 8% had moderate outcome. When the results were related to grades of osteoporosis, grade IV osteoporotic fractures had highest average Constant–Murley score (83 points, range 78–88 points), followed by grade III osteoporotic fractures (80 points, range 71–92 points), followed by grade II osteoporotic fractures (78 points, range 66–88 points). Varus malalignment and subacromial impingement were observed in 8% patients. Loosening of implant and loss of reduction were observed in 4% patients. Superficial infection was observed in 4% patients.

Conclusions

Locking compression plate (LPHP) is an advantageous implant in proximal humeral fractures due to angular stability, particularly in comminuted fractures and in osteoporotic bones in elderly patients, thus allowing early mobilization.
Flexor tendon injuries of the hand treated with TenoFixTM: mid-term results
Authors: Rocchi Lorenzo , Merolli Antonio , Genzini Andrea , Merendi Gianfranco , Catalano Francesco
Published: July 2008

Background

Recently, the Teno FixTMdevice has been detailed in the literature. Conventional stranded cruciate repair requires splinting to protect the sutures from excessive loading, and then, active motion is strongly limited leading to a possible incomplete functional recovery.

Materials and methods

The authors report on their experience in treating 21 patients presenting primary flexor tendon injuries within the digital sheath in zone 2, in all fingers (including the thumb), at an average follow-up of 16 (range: 6-16) months.

Results

There were, according to Strickland and Glogovac criteria: 12 excellent; 6 good; 3 fair.

Conclusions

This new device is practical clinically and can effect strong tendon repairs that withstand early active finger motion, but the best indication is to treat only selected cases of sharp flexor tendon lesions in zone 2. Using this technique it is possible to achieve a quick functional recovery and early return to work.
Mean-Field Behavior for Long- and Finite Range Ising Model, Percolation and Self-Avoiding Walk
Authors: Heydenreich Markus , van der Hofstad Remco , Sakai Akira
Published: July 2008

We consider self-avoiding walk, percolation and the Ising model with long and finite range. By means of the lace expansion we prove mean-field behavior for these models if d>2(α∧2) for self-avoiding walk and the Ising model, and d>3(α∧2) for percolation, where d denotes the dimension and α the power-law decay exponent of the coupling function. We provide a simplified analysis of the lace expansion based on the trigonometric approach in Borgs et al. (Ann. Probab. 33(5):1886–1944, 2005).
Von-Willebrand- und Upshaw-Schulman-Syndrom
Authors: Schneppenheim R. , Budde U.
Published: July 2008

Quantitative und qualitative Defekte des Von-Willebrand-Faktors (VWF) sind für die häufigste hereditäre Blutungsneigung, das Von-Willebrand-Syndrom (VWS), ursächlich, welches überwiegend autosomal-dominant, aber auch -rezessiv vererbt wird. Entsprechend der modularen Struktur des VWF, mit verschiedenen funktionell und strukturell wichtigen Domänen, besteht eine hochgradige Heterogenität sowohl der klinischen Symptomatik als auch der Pathomechanismen. Eine Überfunktion des VWF beruht auf der fehlenden Größenregulation durch seine spezifische Protease ADAMTS13, die mit dem lebensbedrohlichen Krankheitsbild der thrombotisch-thrombozytopenischen Purpura korreliert, einer Störung der Mikrozirkulation durch hyaline Thromben. Deren autosomal-rezessiv vererbte Form, das Upshaw-Schulman-Syndrom, steht auf der anderen Seite der vom VWF verursachten Störungen der Blutgerinnung. Das heutige Wissen um die Pathophysiologie des VWF und seiner Protease ADAMTS13 ermöglicht neben einer rationalen Therapie auch die Erfassung seiner Beteiligung an vaskulären Erkrankungen.
Bcl‐2 and caspase‐8 related anoikis resistance in human osteosarcoma MG‐63 cells
Authors: Lin Dingsheng , Feng Jie , Chen Weishan
Published: July 2008

Detachment of adherent cells from extracellular matrix results in apoptosis, a process termed “anoikis”. Resistance to anoikis is implicated in the progression of many malignancies by facilitating the migration and eventual colonization of distant sites. Human kidney epithelial cells 293T, human osteoblast cells hFOB 1.19 and human osteosarcoma cells Saos‐2 significantly underwent anoikis when adherence was prevented. But human osteosarcoma MG‐63 cells were distinctly anoikis resistant when detached. They formed large aggregates and showed little apoptosis compared to the other cells. When MG‐63 cells were in suspension, caspase‐8, physically associated with death receptor was activated by cell—matrix detachment, whereas. Caspase‐3 and caspase‐9 were not activated. Translational level of Bcl‐2 significantly increased in a time‐dependent manner, but the level of β‐catenin and PI3K did not. Caspase‐8 participates in an anoikis‐inducing process in MG‐63 cells at an early time, and overexpression of Bcl‐2 blocks activation of caspase‐8 making MG‐63 cells anoikis resistant.
N‐terminal acetylation in paenibacillin, a novel lantibiotic
Authors: He Zengguo , Yuan Chunhua , Zhang Liwen , Yousef Ahmed E.
Published: July 2008

N‐terminal acetylation was uncovered in paenibacillin, a novel lantibiotic recently reported as a product of Paenibacillus polymyxa OSY‐DF. This N‐terminal modification is unprecedented among bacteria‐derived antimicrobial peptides and further illustrates the broad range of modifications that can occur in lantibiotics. Additionally, the primary structure of paenibacillin has been finally determined unequivocally by the extensive NMR analysis taken together with previous MS/MS results. These analyses revealed the structure of paenibacillin as one of the most post‐translationally modified lantibiotics.
REEXAMINING THE ROLE OF EXPLICIT INFORMATION IN PROCESSING INSTRUCTION
Authors: Fernández Claudia
Published: July 2008

The present study sought to observe, through online treatments, whether explicit information assists acquisition in a way that has not been measured in previous processing instruction (PI) studies. Two experiments examined learners' behavior while they processed Spanish sentences with object-verb-subject (OVS) word order and Spanish subjunctive under two treatments: with explicit information (the PI group) and without explicit information (the structured input [SI] group). Participants in both groups worked individually with a computer and processed a series of 30 SI items. They received feedback right after each response, and both accuracy and response time were recorded. It was expected that learners in the PI group would start to process both of the linguistic targets sooner in the sequence of input items and would submit their responses faster than learners in the SI group, because explicit information in the PI treatment would help learners notice the target items early in the series. The results showed no difference between the SI group and the PI group when processing OVS sentences, but the PI group processed subjunctive forms sooner and faster than the SI group. The results suggest that the benefits of explicit information might depend on the nature of the task and the processing problem.