bluuebunny/crossref_metadata_2025_split huggingface dataset:
Behavior of quaternary ammonium salt photobase generators on initiating free radical photo‐polymerization
Authors: Zhong Rong , Yang Jianwen , Zeng Zhaohua , Chen Yonglie 
Published: April 2006

AbstractSeries of quaternary ammonium tetraphenyl borates salt photobase generators (PBGs) were synthesized using p‐methoxyphenacylmethylene and 2‐naphthoymethylene as chromophores, and triethylene diamine, pyridine or 3‐methyl pyridine as tertiary amine. The kinetics for polymerization of trimethylolpropane triacrylate (TMPTA) monomer using PBGs as free radical photo‐initiator was monitored by differential photo‐calorimeter (DPC). It was found that all the quaternary ammonium tetraphenyl borate salt photobase generators synthesized could initiate free radical polymerization of the acrylate monomer TMPTA by exposure to UV irradiation, but the activity was relatively low. Addition of a small amount of polar solvent to the system could largely increase the polymerization rate and final conversion. Photo‐polymerization was also improved by increasing light intensity or raising reaction temperature. PBGs with p‐methoxyphenacylmethylene as chromophore had higher absorbance at around 280 nm and showed higher activity in initiating photo‐polymerization than those with N‐(2‐naphthoylmethyl) as chromophore. Copyright © 2006 Society of Chemical Industry
Synthesis and characterization of pH‐ and temperature‐sensitive silk sericin/poly(N‐isopropylacrylamide) interpenetrating polymer networks
Authors: Wu Wen , Li Wenjing , Wang Li Qun , Tu Kehua , Sun Weilin 
Published: April 2006

AbstractInterpenetrating polymer networks (IPNs) composed of silk sericin (SS) and poly(N‐isopropylacrylamide) (PNIPAAm) were prepared simultaneously. The properties of the resultant IPN hydrogels were characterized by differential scanning calorimetry and SEM as well as their swelling behavior at various temperatures and pH values. The single glass transition temperature (Tg) presented in the IPN thermograms indicated that SS and PNIPAAm form a miscible pair. The swollen morphology of the IPNs observed by SEM demonstrated that water channels (pores present in SEM micrographs) were distributed homogeneously through out the network membranes. The swelling ratio of the IPNs depended significantly on the composition, temperature and pH of the buffer solutions. The dynamic transport of water into the IPN membrane was analyzed based on the Fickian equation. Copyright © 2006 Society of Chemical Industry
Interfacial‐initiated seeded emulsion polymerization: preparation of polystyrene/poly(methacrylic acid) core/shell particles in the absence of surfactant
Authors: Liu Wei‐Jun , He Wei‐Dong , Wang Yan‐Mei , Wang De , Zhang Zhi‐Cheng 
Published: April 2006

AbstractComposite polymer particles with hydrophobic polystyrene (PSt) as the core and hydrophilic poly(methacrylic acid) (PMAA) as the shell were prepared through two‐stage emulsion polymerization without any surfactant. In the first step, narrowly distributed PSt seed particles were prepared by surfactant‐free emulsion polymerization with 2,2′‐azobis(2‐methylpropionamide) dihydrochloride (AMPA) as the initiator. In the second step, hydrophilic PMAA shells were fabricated onto PSt seed particles through redox interfacial‐initiated seeded emulsion polymerization with cumyl hydroperoxide (CHPO)/ferrous sulfate/ethylenediaminetetraacetic acid (EDTA)/sodium formaldehydesulfoxylate (SFS), where the initiation took place mainly at the interface between PSt seed particles and the aqueous medium. The composite particles were characterized with transmission electron microscopy, fourier transform infrared spectroscopy and dynamic light scattering, and the results show that a core/shell structure was successfully built. Hydrodynamic radius (Rh) of the composite particles increased with the amount of polymerized monomers in the seeded emulsion polymerization. Copyright © 2006 Society of Chemical Industry
The use of polyelectrolyte stabilisers for suspension polymerisation: the effect of pH on particle size distribution
Authors: Georgiadou Styliani , Brooks Brian W 
Published: April 2006

AbstractAmmonium polymethacrylate (APMA) and sodium polymethacrylate (PMA‐Na) were used as suspending agents for the suspension polymerisation of methyl methacrylate (MMA). The effect of pH on particle sizes and the stabilisation mechanism were examined. Increasing the pH caused a decrease in the particle sizes, and the formation of fine particles with diameters smaller than 10 µm. The amount of suspending agent required to stabilise a monomer dispersion and to prevent coalescence during suspension polymerisation decreases with increasing pH. The prevailing stabilisation mechanism that governs the dispersion stability is probably the electrosteric mechanism. Copyright © 2006 Society of Chemical Industry
Preparation and mechanical properties of clay/polystyrene‐block‐polybutadiene‐block‐polystyrene triblock copolymer (SBS) intercalated nanocomposites using organoclay containing stearic acid
Authors: Yamaguchi Tomohiro , Yamada Eisuke 
Published: April 2006

AbstractOrganoclays containing various amounts of stearic acid (SA) were synthesized, and clay/polystyrene‐block‐polybutadiene‐block‐polystyrene triblock copolymer (SBS) intercalated nanocomposites were prepared using organoclays containing SA by melt‐blending. Montmorillonite was the clay used, and both stearylamine and SA were used as surface modifiers. The amount of SA added was 0, 20, 50 and 100% of the cation‐exchange capacity (CEC). In this study, the effects of SA on the microstructure and mechanical properties of the clay/SBS nanocomposites were investigated. In clay/SBS with 100% CEC of SA, although no exfoliation of the clay occurred, the stacked clay layers were uniformly dispersed at the nanometer level (100–800 nm) without agglomeration. Clay/SBSs containing SA exhibited superior mechanical properties compared to clay/SBS without SA. It was found that SA effectively improved the clay dispersion in the SBS matrix and the mechanical properties of the clay/SBSs. Copyright © 2006 Society of Chemical Industry
Copolymers of acrylic acid with N‐vinylpyrrolidinone and 2‐hydroxyethyl methacrylate as pH‐responsive hydrogels synthesized through a photoinitiator‐free photopolymerization technique
Authors: Ng Loo‐Teck , Swami Salesh 
Published: April 2006

AbstractpH‐sensitive hydrogels for biomedical applications were synthesized using a photoinitiator‐free technique involving the initiation of photopolymerization by donor/acceptor pairs. The differential photocalorimetric technique indicated a high polymerization rate for the N‐vinylpyrrolidinone (NVP, donor)/acrylic acid (AA, acceptor) pair at a 1:1 molar ratio. However, photopolymerization of larger quantities of these monomers (1:1 molar ratio) produced a water‐soluble polymer. Nevertheless, an anionic hydrogel was successfully formed when a small quantity of 2‐hydroxyethyl methacrylate (HEMA) was included in the NVP/AA formulation. A mixture of HEMA and AA, although both are classified as acceptors, photopolymerized to produce a copolymer which functioned as an anionic hydrogel. The swelling and drug release of these hydrogels were investigated in acidic, neutral and basic pH environments. Their biocompatibility with HaCaT human epidermal keratinocyte cells was tested and a positive cell growth as evidenced by the 3‐[4,5‐dimethylthiazol‐2‐yl]‐2,5‐diphenyl tetrazolium bromide (MTT) cell proliferation assay indicated that these hydrogels have no toxic effect on HaCaT. Copyright © 2006 Society of Chemical Industry
Synthesis, characterization and properties of poly(butylene succinate) modified with rosin maleopimaric acid anhydride
Authors: Liu Xiaoqing , Li Chuncheng , Zhang Dong , Xiao Yaonan , Guan Guohu 
Published: April 2006

AbstractHuge hydrogenated phenanthrene ring segments were introduced into the main chain of poly(butylene succinate) by polymerization of succinic acid (SA), 1,4‐butanediol (BD) and rosin maleopimaric acid anhydride (RMA), which was obtained from maleic rosin. The chemical structure and composition of the copolyesters were determined with the aid of 1H‐NMR, FTIR and elemental analysis. The thermal properties, crystallization behaviour and mechanical properties of the copolyester were then investigated using differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), polarized light microscopy (PLM) and mechanical testing. With increasing content of hydrogenated phenanthrene ring segments, the melting temperature, the crystallization temperature and the relative degree of crystallinity decreased gradually, but the elongation at break and the notched impact strength of poly(butylene succinate) were enhanced without a significant deterioration of tensile strength. Copyright © 2006 Society of Chemical Industry
Synthesis and characterization of four‐arm star‐shaped polymers and copolymers
Authors: Wang Tzong‐Liu , Tseng Ching‐Guey 
Published: April 2006

AbstractFour‐arm star‐shaped polymers and copolymers were obtained by transition metal‐catalyzed atom‐transfer radical polymerization (ATRP). The polymers were characterized by FTIR and 1H‐NMR spectroscopy. Gel permeation chromatography results indicated the formation of polystyrene and polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) arms with controlled molecular weights. In dilute solution, the linear polymers had higher inherent viscosities than star‐shaped ones. Thermogravimetric analysis showed a similar degradation mechanism for linear and star‐shaped polymers. Differential scanning calorimetry indicated the successful formation of diblock star‐shaped copolymers. Copyright © 2006 Society of Chemical Industry
Electron‐beam processing of nylon 6 and HNBR blends. Part II: development of high strength, heat‐ and oil‐resistant thermoplastic elastomers
Authors: Das PK , Ambatkar SU , Sarma KSS , Sabharwal S , Banerji MS 
Published: April 2006

AbstractThe effects of electron‐beam irradiation on morphology, mechanical properties and on the heat and hot oil resistance of the thermoplastic elastomeric blend of 30:70 and 70:30, nylon 6 and hydrogenated nitrile rubber (HNBR) were investigated over the dose range 0–8 Mrad. The insoluble content of blends increased with increase in the radiation dose. The morphology of the blend was studied in scanning electron microscopy, with special reference to the effect of radiation prior to processing via injection molding. Irradiated pellets showed better mechanical properties after injection molding compared with irradiated sheets at low radiation dose. The observed differences in mechanical properties are explained on the basis of morphology of the blend. The blend properties were also found to have a strong dependence on nylon content. It was found that the blends rich in nylon had superior mechanical properties, hot oil and solvent resistance, whereas blends with higher HNBR content had better set and heat resistance. The effect of radiation on interaction in these blends was also evaluated and was found to induce possible inter‐chain crosslinking in the blends. Copyright © 2006 Society of Chemical Industry
Synthesis and aggregation behavior of four types of different shaped PCL‐PEG block copolymers
Authors: Lu Chengfei , Guo Sheng‐rong , Zhang Yaqiong , Yin Ming 
Published: April 2006

AbstractBiodegradable, amphiphilic, linear (diblock and triblock) and star‐shaped (three‐armed and four‐armed) poly[(ethylene glycol)‐block‐(ε‐caprolactone)] copolymers (PEG–PCL copolymers) were synthesized by ring‐opening polymerization of ε‐caprolactone (CL) with stannous octoate as a catalyst, in the presence of monomethoxypoly(ethylene glycol) (MPEG), poly(ethylene glycol) (PEG), three‐armed poly(ethylene glycol) (3‐arm PEG) or four‐armed poly(ethylene glycol) (4‐arm PEG) as an initiator, respectively. The monomer‐to‐initiator ratio was varied to obtain copolymers with various PEG weight fractions in a range 66–86%. The molecular structure and crystallinity of the copolymers, and their aggregation behavior in the aqueous phase, were investigated by employing 1H‐NMR spectroscopy, gel permeation chromatography and differential scanning calorimetry, as well as utilizing the observational data of gel–sol transitions and aggregates in aqueous solutions. The aggregates of the PEG–PCL block copolymers were prepared by directly dissolving them in water or by employing precipitation/solvent evaporation technique. The enthalpy of fusion (ΔHm), enthalpy of crystallization (ΔHcrys) and degrees of crystallinity (χc) of PEG blocks in copolymers and the copolymer aggregates in aqueous solutions were influenced by their PEG weight fractions and molecular architecture. The gel–sol transition properties of the PEG–PCL block copolymers were related to their concentrations, composition and molecular architecture. Copyright © 2006 Society of Chemical Industry
From N‐(dinitrophenyl) amino acids to benzimidazole N‐oxides. Synthesis, kinetics and mechanism
Authors: Buján Elba I. , Salum María Laura 
Published: April 2006

AbstractSeveral benzimidazole N‐oxide derivatives were synthesized in very good yields by heating under reflux the corresponding N‐(2,4‐ or 2,6‐dinitrophenyl) amino acid derivative with NaOH in 60% 1,4‐dioxane–H2O. The N‐oxides obtained from glycine and α‐ and β‐alanine derivatives lost the carboxylic group. The observed rate constant for the reaction of N‐(2,4‐dinitrophenyl) glycine (2a) in 10% 1,4‐dioxane–H2O to give 5‐nitro‐1H‐benzimidazole‐3‐oxide (4a) is first order on [NaOH]; the second‐order rate constant is kN=1.7×10−3 M−1 s−1. The mechanism proposed includes the formation of an N‐alkylidene 2‐nitrosoaniline‐type intermediate as the rate‐determining step. Copyright © 2006 John Wiley & Sons, Ltd.
Matrix dependence of blue light emission from a novel NH2‐functionalized dicyanoquinodimethane derivative
Authors: Szablewski Marek , Bloor David , Kagawa Yasuyuki , Mosurkal Ravi , Cole Jacqueline M. , Clark Stewart J. , Cross Graham H. , Pålsson Lars‐Olof 
Published: April 2006

AbstractThe reactions of primary and secondary amines with (cyclohexa‐2,5‐diene‐1,4‐diylidene)‐dimalononitrile (TCNQ) lead to mono‐ and disubstituted dicyanoquinodimethane derivatives and fluorescence emission has been observed for several of these compounds. We report the luminescence properties, synthesis and crystal structure of the novel dicyanoquinodimethane derivative 2‐{4‐[amino‐(2,6‐dimethyl‐morpholin‐4‐yl)‐methylene]‐cyclohexa‐2,5‐ dienylidene}‐malononitrile (Ammor), a unique example of an asymmetric dicyanoquinodimethane derivative in which one of the nitrile groups has been replaced with an NH2 moiety, which provides a reactive centre for potential further substitution or tethering to larger molecules or polymers. The luminescence properties of the title compound were investigated in a variety of environments, including alcohol solutions at room temperature and a glass‐forming solvent at low temperature. The fluorescence quantum yields and Stokes' shifts of the blue emission were found to be very sensitive to the matrix. The crystal structure of the subject compound was determined, revealing that the molecules are non‐planar in the ground state. The environmentally sensitive emission is discussed in terms of the conformational change during photoexcitation and the constraint imposed on this by the matrix. This behaviour is also compared with that of other related amino‐functionalized dicyanoquinodimethane derivatives. Copyright © 2006 John Wiley & Sons, Ltd.
Conformational properties of C2v‐symmetrical resorcin[4]arene tetraethers
Authors: Morikawa Osamu , Iyama Eiichi , Oikawa Tomoyoshi , Kobayashi Kazuhiro , Konishi Hisatoshi 
Published: April 2006

AbstractResorcin[4]arene tetraether derivatives, in which a resorcinol unit and a 1,3‐dialkoxybenzene unit are incorporated in an alternating order, were synthesized by the Sc(OTf)3 catalyzed ‘2 + 2’ fragment condensation. The conformational properties were studied using variable temperature 1H‐NMR spectroscopy, indicating that the resorcinarenes are flexible at room temperature but frozen in the cone formation at −90 °C in CD2Cl2, and they interconvert between two equivalent cone conformations with an energy barrier of ΔGc‡ = 10.2–10.5 kcal mol−1. These values are slightly lower than that for the resorcin[4]arene containing four 2‐hexylresorcinol units. The cone conformation is stabilized by intramolecular hydrogen bonds between the OH hydrogen and ether oxygen, which is evidenced by the low frequencies (3423–3434 cm−1) of the OH‐stretching vibrations in CDCl3 solution. Copyright © 2006 John Wiley & Sons, Ltd.
Partition of polyhydroxy compounds of biological and pharmacological significance between AOT reverse microemulsions and aqueous salt solutions
Authors: Reta Mario , Waymas Omar , Silber Juana J. 
Published: April 2006

AbstractThe partition behavior of shikimic acid, gallic acid, gallotannic acid, rutin and quercetin between reverse microemulsions of the surfactant bis(2‐ethylhexyl) sulfosuccinate (AOT) and aqueous salt solutions of LiCl, NaCl and KCl at different salt concentrations and pH was studied. Quantification of the extracted analytes was performed by HPLC on an octadecyl silica column using a methanol–buffer mobile phase at pH 3.0. Clean‐up before injection was not needed because the micellar organic phase was compatible with the HPLC mobile phase. A solvent gradient was used to elute all compounds and the surfactant in a reasonable time. The extraction from the aqueous media is fast and reproducible. Different solubilization behavior was observed by changing the salt concentration and the type of cation in the aqueous phase. By proper selection of the experimental conditions, it is observed that shikimic acid and gallic acid remain mostly in the aqueous phase, whereas significant amounts of gallotannic acid and rutin are transferred to the micellar phase in only one contact and quercetin is completely solubilized in this phase. Thus, the different solubilization behavior that these compounds exhibit in the AOT micellar media can be very useful for extraction and preconcentration purposes. Copyright © 2006 John Wiley & Sons, Ltd.
Plasma‐Based De‐Pyrogenization
Authors: Kylián Ondřej , Hasiwa Marina , Rossi François 
Published: April 2006

AbstractSummary: Applicability of low‐pressure microwave discharges for the de‐pyrogenization of the heat sensitive materials has been tested. It has been found that discharges in selected gas mixtures are capable to reduce the amount of deposited pyrogens significantly within 1 min of plasma treatment. Moreover, it has been demonstrated that de‐pyrogenization is due to the plasma interactions with the pyrogens, and it cannot be ascribed to other possible side effects.Time evolution of de‐pyrogenization in a O2:H2 (50:50) microwave discharge.magnified imageTime evolution of de‐pyrogenization in a O2:H2 (50:50) microwave discharge.
Surface Analysis of Plasma Deposited Polymer Films, 7
Authors: Oran Umut , Swaraj Sufal , Lippitz Andreas , Unger Wolfgang E. S. 
Published: April 2006

AbstractSummary: Plasma deposited allylamine films were studied by “in situ” ToF‐SSIMS, XPS and NEXAFS Spectroscopy before exposure to ambient air. The influence of external plasma parameters such as duty cycle, plasma power, and monomer flow rate on (i) unsaturation, (ii) branching and cross‐linking, (iii) nitrogen surface concentration and (iv) retention of amino groups was investigated. Harder plasma conditions, which can be obtained when high duty cycles, high plasma power, and low monomer flow rates are employed, increase the unsaturated, branched and cross‐linked character of the plasma deposited films, while the surface concentration of N as well as the retention of the monomer's amino group decrease. As proven by NEXAFS findings and cross‐checked by ToF‐SSIMS results, the allylamine monomer's primary amino groups are partially transformed into other nitrogen functionalities during its plasma polymerization. Amongst them imines and nitriles are the conversion products with the highest probabilities of formation. Another conversion channel is the formation of nitrogen species not participating in the film growth. This is the reason for an increased N loss in plasma deposited allylamine films as observed independently by XPS and ToF‐SSIMS when the plasma parameters are changed from mild to hard.Summations of π*(CN) and π*(CN) resonance intensities for NEXAFS N K‐edge spectra measured with plasma deposited allylamine films vs. variation of duty cycle, or power.magnified imageSummations of π*(CN) and π*(CN) resonance intensities for NEXAFS N K‐edge spectra measured with plasma deposited allylamine films vs. variation of duty cycle, or power.
Stop‐flow kinetics studies of the interaction of surfactant, sodium dodecyl sulfate, with acid‐denatured cytochrome c
Authors: Xu Qi , Keiderling Timothy A. 
Published: April 2006

AbstractInteractions of sodium dodecyl sulfate (SDS) at submicellar and micellar concentration, with the globular protein, horse heart cytochrome c, at low pH have been shown to stabilize two molten globule‐like intermediates. These dynamic studies were performed using far‐UV, near‐UV, and Soret‐band circular dichroism (CD) as well as fluorescence methods. Stopped‐flow CD and fluorescence studies of acid‐denatured cytochrome c refolding with SDS were performed at both submicellar and micellar concentrations. Distinctive refolding mechanisms (from analysis of both CD and fluorescence) were found under these two conditions, and an obvious refolding intermediate was evident in the fluorescence traces. In addition, stopped‐flow CD in the Soret region showed multistep kinetics, suggesting that the spectral changes in this region are not only solvent effect related but also connected with the change of secondary structure. A possible folding mechanism is proposed to rationalize the kinetics results. Proteins 2006. © 2006 Wiley‐Liss, Inc.