bluuebunny/crossref_metadata_2025_split huggingface dataset:
Arsenic induced progesterone production in a caspase‐3‐dependent manner and changed redox status in preovulatory granulosa cells
Authors: Yuan Xiao‐Hua , Lu Cai‐Ling , Yao Nan , An Li‐Sha , Yang Bai‐Qing , Zhang Chuan‐Ling , Ma Xu 
Published: March 2011

AbstractArsenic contamination is a principal environmental health threat throughout the world. However, little is known about the effect of arsenic on steroidogenesis in granulosa cells (GCs). We found that the treatment of preovulatory GCs with arsenite stimulated progesterone production. A significant increase in serum level of progesterone was observed in female Sprague–Dawley rats following arsenite treatment at a dose of 10 mg/L/rat/day for 7 days. Further experiments demonstrated that arsenite treatment did not change the level of intracellular cyclic AMP (cAMP) or phosphorylated ERK1/2 in preovulatory GCs; however, progesterone production was significantly decreased when cAMP‐dependent protein kinase (PKA) or ERK1/2 pathway was inhibited. This implied that the effect of arsenite on progesterone production may require cAMP/PKA and ERK1/2 signaling but not depend on them. Furthermore, we found that arsenite decreased intracellular reactive oxygen species (ROS) but increased the antioxidant glutathione (GSH) levels and mitochondrial membrane potential (ΔΨm) in parallel to the changes in progesterone production. Progesterone antagonist blocked the arsenic‐stimulated increase of GSH levels. Arsenite treatment induced caspase‐3 activation, although no apoptosis was observed. Inhibition of caspase‐3 activity significantly decreased progesterone production stimulated by arsenite or follicle‐stimulating hormone (FSH). GSH depletion with buthionine sulfoximine led to cell apoptosis in response to arsenite treatment. Collectively, this study demonstrated for the first time that arsenite stimulates progesterone production through cleaved/active caspase‐3‐dependent pathway, and the increase of GSH level promoted by progesterone production may protect GCs against apoptosis and maintain the steroidogenesis of GCs in response to arsenite treatment. J. Cell. Physiol. 227: 194–203, 2012. © 2011 Wiley Periodicals, Inc.
Synthesis and properties of multiblock copolymers of styrene and propylene oxide
Authors: Xie Hongquan , Chen Xin 
Published: March 2011

AbstractMultiblock copolymers of styrene and propylene oxide were synthesized by coupling together poly(propylene glycol) and telechelic dihydroxy‐polystyrene with 2, 4‐toluene diisocyanate(TDI) as the coupling agent. The results showed that it was better to terminate the telechelic dihydroxy polystyrene with TDI first, then react with poly(propylene glycol). The copolymer obtained in this two‐step method contains less homopolymers than that obtained when all the three reagents reacted together in one step. The crude product can be purified by extractions with absolute ethyl alcohol and decalin in order to remove the unreacted poly(propylene glycol) and polystyrene, respectively. The purified products were characterized by IR, TH NMR, GPC, membrane osmometry, elemental analysis and shown to be multiblock copolymers of styrene and propylene oxide. The multiblock copolymer exhibits two transition temperatures(Tg's) and behaves like a thermoplastic elastomer at 20–30% polystyrene content. Addition or 2% of the copolymers to the blends of polystyrene and epichlorohydrin rubber improves evidently their mechanical properties and causes the two Tg's to become closer.
Graft copolymerization of vinylpyridines onto cellulosic fibres by the ceric ion method. The monomer concentration effect
Authors: Leza M. L. , Casinos I. , Guzmán G. M. 
Published: March 2011

AbstractThe effect of monomer concentration on the graft polymerization of 4‐vinylpyridine (4‐VP) and of 2‐vinylpyridine (2‐VP) on cellulose and on partially carboxymethylated cellulose (PCMC) initiated by cerium ammonium nitrate (CAN) in dilute nitric acid has been examinated. The grafting parameters: grafting efficiency (GE), graft yield (G), graft frequency (GF), and ceric ion consumption ((Ceiv)c)were studied as a function of the monomer concentration. The fraction of poly(4‐vinylpyridine), P(4‐VP), in the graft polymer increased with increasing monomer concentration for both cellulosic substrates. The molecular weight of the grafted P(4‐VP) was obtained viscosimetrically after hydrolyzing away the cellulose backbone. When 2‐VP was grafted on PCMC and on unmodified cotton, the graft yields also increased with monomer concentration, but they were much smaller than in the previous case. Presence of carboxymethyl groups in cellulose enhanced G, GE, Mv, and GF.
Towards a generalization of stereospecific nucleophilic substitution of PVC
Authors: Millán J. , Martínez G. , Mijangos C. , Méndez A. , Gómez‐Elvira J. M. , Gómez‐Daza M. 
Published: March 2011

AbstractTwo series of nucleophilic substitution reactions on PVC using either the same nucleophile but different experimental conditions or various nucleophiles in cyclohexanone (CH) dilute solutions, were performed. The evolution of unreacted iso‐, hetero‐and syndiotactic triads with degree of conversion was followed by 13 C NMR. While the kinetics and yield changed markedly with both the type of nucleophile and the reaction conditions the stereochemical structure of modified polymers proved to depend only on degree of substitution. These results afford further support to a conformational mechanism of substitution, as proposed by earlier works.
Some developments in the study of radical polymerization
Authors: Bevington John C. 
Published: March 2011

AbstractStudies of initiation by azobis(isobutyronitrile) and benzoyl peroxide are discussed. Consideration is given to initiators containing carbon‐13 or carbon‐14 for end‐group analyses, and also to the applications of radical‐trapping techniques for study of oxygen‐centred radicals. Other topics dealt with are (a) head‐addition of primary radicals to monomers, (b) the formation of end‐groups by primary radical termination and by transfer to initiator, and (c) the involvement of stilbene‐like compounds in initiation.
Galvinoxyl as scavenger in the radical polymerization of styrene initiated by AIBN
Authors: Areizaga J. F. , Guzmán G. M. 
Published: March 2011

AbstractThe initiation of the polymerization of styrene by AIBN has been studied at 59, 8°C and 69, 9°C, using Galvinoxyl as a free radical scavenger, by spectrophotometric means. Rates of 7×10−9 and 2×10−8 mol·1−1 · s−1 have been measured for the scavengeable free radicals formation in the initiation process of the thermal polymerization of pure styrene, respectively. Values of 6×10−6 s−1 and 2, 4×10−5 s−1 have been obtained for the rate constants of production of scavengeable pairs of free radicals (kdf) from AIBN assuming an ideal kinetic scheme.
Template polymerization of N‐vinylimidazole along poly(methacrylic acid)
Authors: van De Grampel H. T. , Tan Y. Y. , Challa G. 
Published: March 2011

AbstractThe radical polymerization of N‐vinylimidazole (VIm) along an atactic poly(methacrylic acid) (PMAA) template in aqueous solution at 50°C was investigated by varying [PMAA]0 from 0 to 0.7 basemol/dm3 at constant [VIm]0 of 0.41 mol/dm3. Rate enhancements were observed only beyond [PMAA]0 of 0.18 basemol/dm3. By studying the initial pH and ηsp/c of the polymerization mixtures and taking account of preferential adsorption of protonated VIm on PMAA, part of which is probably mobile, a mechanism is suggested.
The observation of polymer microstruture by NMR
Authors: Bovey F. A. 
Published: March 2011

AbstractNuclear magnetic resonance (NMR) is a method of great importance for the study of most aspects of the structure and behavior of polymers. In this review, I deal with its application to the observation of the detailed structure of polymer chains, particularly those of vinyl and diene polymers and copolymers. This is for the most part accomplished using polymer solutions, but NMR also allows one to observe chain structure and conformation in the solid state by means of magic angle spinning and high power proton decoupling.
Use of small‐angle neutron scattering to investigate the morphology of some polymeric materials
Authors: Hammouda Boualem 
Published: March 2011

AbstractSmall‐angle neutron scattering is a molecular probe to monitor chain conformations in partially deuterated polymers. It can also be used to investigate the morphology of microphase segregated multiphase systems. It offers a means of understanding polymer microstructure, which can then be related to physical properties and sample treatments. This technique is applied here to the problem of macromolecular orientation in polystyrene subject to hot‐stretching as well as to a block copolymer system (50/50 mixture of bisphenol A carbonate and dimethylsiloxane). A general description of the technique as well as specific results are discussed.
Electron spectroscopic imaging studies on polyethylene, chain‐folded and extended‐chain crystals
Authors: Kunz M. , Möller M. , Heinrich U.‐R. , Cantow H.‐J. 
Published: March 2011

AbstractDiscrimination of elastically and inelastically scattered electrons in transmission electron microscopy (TEM) yields electron micrographs with enhanced and specific contrast. Highly resolved micrographs can be obtained in which the contrast reflects the local concentrations of specific elements. In the present work, Electron Spectroscopic Imaging (ESI) by means of a Zeiss EM 902 TEM are reported for a series of differently crystallized polyethylene samples. Excellent contrast can be achieved without staining. The different techniques allow easy verification of the observed morphology.
Characterization of piezoelectric polymers with the aid of NMR
Authors: Chûjô Riichirô 
Published: March 2011

AbstractPiezoelectric polymers, poly(vinylidene cyanide‐co‐vinyl acetate), poly(vinylidene cyanide‐co‐vinyl benzoate), and related polymers were characterized with the aids of NMR on the following items:copolymer compositionstereoregularityconformationsegmental motion.In a series of the above items, the most significant difference was found in segmental motion between piezoelectric and non‐piezoelectric polymers; larger segmental mobility may be essential for poling process, while smaller mobility is convenient for the maintaining of piezoelectricity after poling.
Study of phase transitions and curie temperature in ferroelectric copolymers of PVF2 using synchrotron radiation techniques
Authors: Cabarcos E. López , Arche A. Gonzalez , Calleja F. J. Baltá , Zachmann H. G. 
Published: March 2011

AbstractReal time wide angle (WA) and small angle X‐ray scattering (SAXS) data from 70/30 and 80/20 vinylidene fluoride/trifluoroethylene copolymers are reported as a function of temperature during crystallization from the melt. The para‐ferroelectric Curie transition detected from DSC and WAXD experiments in the temperature interval 70–40°C for the 70/30 copolymer and in the range 90–60°C for the 80/20 material are associated to a sudden increase of the integrated SAXS intensity. Comparison of experimental and calculated data based on a sandwich model of crystals alternated by amorphous layers supports the view of a coexistence of para‐ and ferroelectric phases within the crystalline material through the transition range studied.
Thermodynamics of polymer solutions and blends
Authors: Kleintjens L. A. , Koningsveld R. 
Published: March 2011

AbstractPolymerization reactions are quite often accompanied by liquid‐liquid phase separations. Processing of polymer blends is commonly also based on the phase behaviour of the system; for some applications homogenous blends are to be obtained while for other two‐phase systems are desired. Experimental methods suitable for gaining insight into the thermodynamic behaviour in such viscous systems will be discussed and some relevant measurements, performed by equilibrium methods, will be shown.Classic thermodynamic equilibrium considerations, based on simple molecular models lead to useful descriptions and predictions of the phase behaviour of partially miscible polymer systems. Depending on the amount of experimental information and on the complexity of the polymeric system, predictions will be more or less quantitative. Solubility parameter and group contribution approaches present the first level, and such predictions indicate whether a system is miscible or not.The second level of description is given by Flory‐Huggins‐Staverman approaches. These models call for some experimental evidence but permit estimation of the location of miscibility gaps and their dependence on the polymer molar mass. The concentration ranges of the demixed region are usually not well presented by these models.The quality of the description is improved considerably when the disparity of size and shape between the repeat units of the polymer and solvent constituents are taken into account. On this third level the influence of pressure can be included in the model and reasonable descriptions of the P‐T‐x space can be obtained.Extensions to copolymer systems are being developed nowadays, but still fail to give quantitative representation of the actual complex phase behaviour of such systems.
Microcalorimetric studies of the complexation between poly(ethylene oxide) and alkaline salts in solution
Authors: Daoust Hubert , Cloutier Bruno 
Published: March 2011

AbstractA series of microcalorimetric measurements have been done on complex formation between poly(ethylene oxide) (PEO) and some alkaline metal salts in solution at 25°C. Heat of complexation measurements as a function of PEO content were done with a Tian‐Calvet microcalorimeter and heat capacity measurements have been done with a Picker dynamic microcalorimeter. A very weak exothermic interaction between the species has been found for the PEO‐KSCN pair in water indicating that complexation is difficult to obtain due to the important hydration of both solutes. However, a comparatively large exothermic interaction has been observed for the same pair in anhydrous methanol. Exothermic interactions have also been found for PEO‐KI, ‐NaI and ‐LiI systems in methanol with decreasing absolute values for heats of complexation going from KI to LiI. In methanol, heats of complexation pass through a rather flat and broad maximum at PEO/salt molar ratios going from 1:1 to 4:1 for KSCN and KI. For NaI, the maximum appears for a molar ratio of 2:1 and for LiI, this ratio is 4:1. Heat capacity measurements do not indicate any specific feature for any of the systems except in the case of KSCN in methanol. Experimental results are discussed in terms of ion size and of ion solvation.
Preferential and total sorption in the systems methacrylic polymer/toluene + butyl chloride
Authors: Katime Issa A. , Huglin M. B. , Sasía P. M. 
Published: March 2011

AbstractViscometric, dialysis equilibrium differential refractometry. densitometric and light scattering measurements have been performed for three different polymethacrylates: poly(methyl methacrylate). poly(butyl methacrylate) and poly(cyclohexyl methacrylate) in toluene/butylchloride binary mixture at 298 K. We have measured the preferential and total sorption to the polymer chain by the solvents, the Mark‐Houwink‐Sakurada parameters and the B interaction parameter. We have drawn conclusions about the liquid‐liquid and polymer‐liquid interactions, trying to explain the influence of the polymer side group in its solution behaviour.
On the miscibility and interchange reactions in bisphenol a polycarbonate/nylon 6 blends
Authors: Eguiazábal José Ignacio , Nazábal Jon 
Published: March 2011

AbstractThe miscibility and the interchange reactions in bisphenol A polycarbonate/nylon 6 blends prepared by melt mixing have been studied by means of the torque‐time relationships, calorimetric analysis and solubility tests. The results indicate that the blends are partially miscible and also the existence of interchange reactions between the polymers when they are melt‐mixed.
Morphologies and regimes of growth of polybutene crystals in phase II
Authors: Monasse Bernard , Haudin Jean Marc 
Published: March 2011

AbstractThe growth rates of two poly(1‐butene) with different molecular weights have been deduced from microscopic observations and the corresponding morphologies have been described. In both polymers two changes in the growth regime are observed and interpreted according to Hoffman's kinetic theory of polymer crystallization. The main nucleation parameters can be determined from the growth regime transitions when the relevant formulations of the kinetic and the transport laws have been selected, taking into account the large range of crystallization temperature.
Crystallization and melt behaviour of poly(vinylidene fluoride) + poly(vinyl alcohol) blends
Authors: Katime Issa A. , Quintana José R. , Cesteros Luis C. , Peleteiro María C. 
Published: March 2011

AbstractMelting and crystallization behaviour of poly(vinylidene fluoride) (PVF2)/poly(vinyl alcohol) (PVAL) blends have been analyzed. From Hoffman‐Weeks plots we have found that an appreciable melting point depression of PVF2 does not exist. On the other hand, we have found that the presence of PVAL affects the morphological factor γ, which is not constant with the composition of the blend. This factor suggests that the melting behaviour of this system depends on kinetics effects. The kinetics of isothermal crystallization was analyzed by means of the Avrami equation.
Rheological properties of thermotropic polyester‐based gels
Authors: Muñoz M. E. , Gallego F. , Peña J. J. , Santamaría A. 
Published: March 2011

AbstractCooling concentrated solutions of the aromatic copolyester poly(ethylene terephthalate‐co‐p‐benzoate)(60 mol‐% p‐benzoate units)in m‐cresol results in gels whose viscoelastic properties are studied in this paper.The gelation process is monitored in a Couette‐type viscometer. From the gelation temperature an enthalpy of formation of ΔHa = 3 kcal/mol is obtained. Dynamic viscoelastic measurements are also carried out, and the theory of rubber elasticity is applied to a well‐defined temperature and frequency independent modulus.From the obtained results we suggest that hydrogen bonds between carbonyl groups of the chain backbone and hydroxyl hydrogens of the solvent are responsible for gel formation.
Liquid crystalline solutions of poly(α‐isobutyl‐L‐aspartate)
Authors: Montserrat J. M. , Muñoz‐Guerra S. , Subirana J. A. 
Published: March 2011

AbstractPoly(α‐isobutyl‐L‐aspartate), abbreviated PAIBLA, is a helical polymer. In this paper we evaluate its potential to form liquid crystals. We have observed highly birefringent solutions in helicogenic solvents as chloroform and dichloromethane. They were further characterized by PMR spectroscopy, and hydrodynamic and optical measurements. From these solutions, solid films were cast which displayed a uniplanar orientation with helical molecules lying parallel to the film surface. We conclude that PAIBLA is capable of forming lyotropic liquid crystals with a cholesteric structure.
On the behaviour of the elongational viscosity of a nematic polymer in elongational flow
Authors: Diogo A. C. 
Published: March 2011

AbstractFor nematic materials, the elongational viscosity depends on the orientation of the director field relative to the velocity field. A computation of the elongational viscosity for various flow geometries is presented. It is shown that for uniaxial elongational flow the director aligns along the flow direction with a characteristic time τE = −2γ1/(3γ2ϵ); for planar elongational flow, the director aligns perpendicular to the flow with a characteristic time τE2 = ‐γ1/(γ2ϵ).
Stress‐strain behavior of polyacrylamide networks
Authors: Baselga J. , Piérola I. F. , Hernández‐fuentes I. , Llorente M. A. 
Published: March 2011

AbstractThe mechanical properties of a number of polyacrylamide gels have been studied by means of elastic measurements in elongation. Different gels were prepared by varying the proportions of both comonomers, acrylamide and N, N‐methylene‐bisacrylamide which is used as crosslinker, and a very broad range of concentrations was covered. The most important results considered were the elastic phantom modulus, the degree of (equilibrium) swelling and the elongation at rupture. The data were interpreted in terms of the mechanism of the gelation process taking into account a number of parameters that affect the final structure of the gels: comonomer reactivities, sequence length distributions and cycles formation. Consideration of these factors can explain properly all the features of the elastic results as well as some other properties related to the gelation process such as gel point data.
Analysis of enthalpy relaxation in amorphous poly(ethylene terephthalate)
Authors: Montserrat S. , Cortks P. 
Published: March 2011

AbstractEndothermic peaks below or superposed to Tg have been observed by Differential Scanning Calorimetry in samples of amorphous poly(ethy1ene terephthalate) (PET) which were submitted to a wide range of annealing conditions. These endothermic peaks allow the obtention of the excess of enthalpy (6) and subsequently the effective relaxation times T(eff) On applying an empirical equation of T∼∼, with separate contribution of temperature and structure (6), kinetic parameters have been found in a range close to Tg, resulting for PET an apparent activation energy of 860.5 kJ/mol (between 60 and 68OC). This parameter has been also calculated from de dependence of Tg with the heating rate in a DSC scan and the values found are between 314 and 419 kJ/moL
Study of the molecular origin of the mechanical and dielectric β relaxation of methyl methacrylate/isopropenyl methyl ketone copolymers
Authors: Ribes‐Greus A. , Soria V. , Figueruelo J. E. , Díaz‐calleja R. 
Published: March 2011

AbstractA study of the β relaxation in a series of methyl methacrylate and isopropenyl methyl ketone copolymers by dielectric, mechanical and thermally stimulated current methods has been carried out. It is observed that the position on the axis of temperature and height of the β relaxation is nearly the same in all the pure polymer and in the two copolymers. This points out that the molecular origin of the β relaxation is related to the partial rotation of the alkoxycarbonyl group in the side chains. However, the apparent activation energy of the β relaxation seems to have a smooth energy distribution, which we have associated with the intermolecular barrier that opposes to this relaxation.
Mechanical properties of two interpenetrating networks
Authors: Poussin D. , Lataillade J. L. , Pouyet J. 
Published: March 2011

AbstractInterpenetration of polyepoxide, polyurethane and polyester networks leads to matrix for high performance composites. The increase of ultimated elongation, shock resistance is due to a mechanical homogeneization, because of a better stereometric organization. On the other hand, it seems that this does not contribute to the rubber plateau behaviour, the molecular mass between crosslinks and the glassy transition.