bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractDifferent 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

AbstractA 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractDetailed 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractPolymer 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

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

AbstractCyclotrimethylenetrinitramine (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

AbstractDouble‐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

AbstractElectron‐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

AbstractThe 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

AbstractIn 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)