bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic mechanical behaviour of a polysulfone in the glass transition region
Authors: Macho E. , Alberdi J. M. , Alegría A. , Colmenero J. 
Published: March 2011

AbstractDynamic mechanical measurements on commercial samples of a polysulfone have been performed at different frequencies at a temperature range from 400 to 510 K. Bending mode measurements were carried out in a Standard Polymer Laboratories DMTA apparatus, which simultaneously delivers both real and imaginary components of Young's complex modulus. Two main dispersion regions are apparent in the relaxation spectrum, the mechanical α‐relaxation, located at temperatures just above the calorimetric glass‐transition, and the high temperature dispersion process, which is related to the behaviour of the entanglement network. Master curves have been built from the experimental data. Shift factors corresponding to the two dispersion processes have been well fitted by only one Vogel‐Fulcher law. Below Tg, shift factor deviates towards an Arrhenius‐like behaviour which has been associated to a low strength sub‐Tg relaxation. Master curves allow the shape parameters of the two main dispersion processes to be calculated. Values obtained indicate that the dispersion process associated to the glass transition arises from a relatively high‐coupled intra‐cluster molecular motion with a nearly random cluster size distribution. However, the high temperature (low frequency) dispersion process seems to arise from the motion of units with weaker coupling.
On the microhardness of irradiated polycarbonate
Authors: Bajpai R. , Keller J. M. , Datt S. C. 
Published: March 2011

AbstractPolycarbonate specimens were irradiated with gamma irradiation doses ranging from 2–75 Mrad. Vickers hardness number (Hv) of these specimens has been calculated. It has been found that Hv decreases with irradiation dose upto 50 Mrad and thereafter it suddenly increases at 75 Mrad. This variation of Hv with gamma irradiation has been explained on the basis of scissioning and crosslinking in polymers.
Microhardness measurement of polypropylene, poly(ethylene terephthalate) and poly(tetra‐fluoroethylene)
Authors: Parashar P. , Bajpai R. , Keller J. M. , Datt S. C. 
Published: March 2011

AbstractMicrohardness studies of commercially available polypropylene, poly(ethylene terephthalate) and poly(tetrafluoroethylene) have been carried out to investigate the effect of load on Vickers hardness number. The nature of the polymers have also been explained on the basis of the logarithmic index n and small stress behaviour with the help of Newtonian resistance pressure.
The use of subcomponents for the prediction of the mechanical behaviour of polypropylene injection moulded products
Authors: Cunha A. M. , Pouzada A. S. , Oliveira M. J. , Crawford R. J. 
Published: March 2011

AbstractThe mechanical performance of injection moulded products is strongly dependent on the processing conditions due mainly to the way in which these affect the microstructure of the moulded material. This paper presents a new approach to this problem whereby the mechanical behaviour is predicted using data obtained from subcomponents, such as discs. These were moulded in polypropylene using different gate types and moulding conditions (injection rate and mould temperature). The microstructure of the subcomponents was examined by polarized light microscopy to assess the average size of the spherulites and the skin/wall thickness ratio. These were then related to the mechanical properties of the subcomponents as characterized by a three point bending test and by an instrumented tensile impact test. The paper presents the data obtained and describes the correlation between processing structure and mechanical behaviour. The value of this subcomponent approach is illustrated through its application to some commercial mouldings.
The relationship between processing conditions, morphological structure and mechanical properties of knit lines of an injection molded semi‐crystalline thermoplastic
Authors: Singh D. , Moslé H. G. 
Published: March 2011

AbstractThe structure‐property relationship of injection molded polypropylene samples with knit lines was investigated. Double gated tensile bars were injection molded under different molding conditions in order to study the influence of molding parameters on crystallinity and spherulite diameter. It was observed that the degree of crystallinity and spherulite size were highly dependent on cooling rate. To improve weld line strength and elastic modulus, an increase in crystalline fraction and the diameter of the crystalline aggregates seems to be necessary.
A kinetic model for network formation in free radical polymerization
Authors: Tobita H. , Hamielec A. E. 
Published: March 2011

AbstractA new model for gelation in free radical polymerization based on the pseudo‐kinetic rate constant method is proposed. This model which considers all of the important reactions in free radical polymerization can be used to make calculations of the average properties during network formation. The model is more general than the statistical model based on Flory/Stockmayer treelike concepts and under special limiting conditions reduces to the Flory/Stockmayer model. The present model is easy to use and provides greater insight into the phenomenon of gelation and growth and structure of crosslinked polymers synthesized by free radical polymerization.
The role of the cosurfactant in the miniemulsion copolymerization of vinyl acetate and n‐butyl acrylate
Authors: Delgado J. , El‐Aasser M. S. , Silebi C. A. , Vanderhoff J. W. 
Published: March 2011

AbstractThe role of the cosurfactant in the miniemulsion copolymerization process of 50:50 molar ratio vinyl acetate/n‐butyl acrylate miniemulsion copolymerization is analyzed. The mixed emulsifier system used to prepare the miniemulsions was sodium hexadecyl sulfate as surfactant and hexadecane as cosurfactant. It is shown that even though hexadecane plays an important role in the distribution of the monomers between the different phases present during the copolymerization process, it does not greatly affect the kinetics. It is the presence of stable submicron droplets what really alters the kinetics by shifting the particle nucleation mechanism from the aqueous phase to the monomer droplets.
Charge carrier transport in polymers: A view by thermally stimulated currents
Authors: Zieliński Marek , Plans Joaquin 
Published: March 2011

AbstractThermally Stimulated Currents (TSC) technique is widely used to study electronic properties of polymers. In this paper we will sketch the history of how this technique was applied to look at basic phenomena in electrical conduction: generation and transport of charge carriers, electrons and holes. We will also discuss the latest developments in the analysis of the TSC spectra, including the transport and release peaks.
Thermally stimulated and isothermal discharges of corona‐charged polypropylene
Authors: Singh Ranjit , Keller J. M. , Datt S. C. 
Published: March 2011

AbstractDetailed investigation of short‐ and open‐circuit thermally stimulated currents (TSC's) along with that of isothermal charge decay and absorption currents have been made on corona‐charged 40 μm thick commercial‐grade polypropylene (PP) foils. Comparison of two types of TSC's revealed that the polymer is characterized by energetically deep surface traps giving rise to a 145°C peak in open‐circuit TSC's. However, the other three peaks occurring at temperatures below 145°C in both types of TSC's are concluded to be due to bulk traps. The observed anomalous TSC's flowing in the same direction as the charging current at higher values of polarizing field and temperature have been considered to be due to space‐charge injection assisted by localized states and the blocking nature of the electrodes. The equivalence between TSC and discharge techniques has been established.
Etude comparative de la conductivite dans des films et des plaquettes de polymeres electroactifs (PPS et PPP) dopes par implantation ionique
Authors: Moliton A. , Duroux J. L. , Ratier B. , Froyer G. , Pelous Y. 
Published: March 2011

AbstractIn our laboratory, we have studied in a systematic way, ion effect on the conductivity of the polyparaphenylene (PPP) versus implantation parameters. In a first time, we have made a basic study on PPP pallets, and then compared these results with the other ones obtained with PPP and PPS (polyphenylene sulfide) films.
Conducting injection moulded carbon black filled polyethylene
Authors: Baltá calleja F. J. , Bayer R. K. , Ezquerra T. A. , Salazar Martinez J. , Zachmann H. G. 
Published: March 2011

AbstractCarbon black filled polyethylenes were prepared by injection moulding using a mould which induces elongational flow. In case of high molecular weight matrices, a microadditive segregation within the material leads to conductivity values σ ≈ 10−1 ω−1 cm−1 which are much larger than those obtained for the compression moulded material. The use of lower molecular weight matrices leads to lower conductivity levels. This is attributed to a less pronounced destruction of carbon black agglomerates during the mixing process and to an orientation effect of these particles by injection flow.
Recent developments in the synthesis and functionalization of conducting poly(thiophenes)
Authors: Roncali Jean , Garreau Robert , Delabouglise Didier , Garnier Francis , Lemaire Marc 
Published: March 2011

AbstractThe mechanism of the electropolymerization of thiophene derivatives has been investigated by varying the electrosynthesis conditions and the monomer structure. The results of these analyses led to the definition of optimized electrosynthesis conditions allowing the control of the electrical and electrochemical properties of poly(thiophenes). On the basis of these results, the properties of these polymers have been modified by means of a new one‐step electrosynthesis of conducting composite materials and by the direct electropolymerization of tailor‐made functionalized monomers. For this purpose, the steric conditions associated to the various possibilities of covalent derivatization have been analyzed, leading to the definition of a “functionalization space”, compatible with the preservation of high conductivity and electrochemical reversibility in the resulting polymers. This concept has been applied to the synthesis of highly conducting chiral poly(thiophenes) on which an effect of enantioselective molecular recognition has been demonstrated for the first time.
Modification of poly(N‐vinylcarbazole): Nitration and thermally stimulated depolarization current study
Authors: Zamora Fernando , Del Carmen Gonzalez Maria , Del Val Juan José 
Published: March 2011

AbstractIn order to introduce some electronic affinity in poly(N‐vinylcarbazole), we proceeded to incorporate NO2 groups in its pendant aromatic group. Two samples obtained by different polymerization processes were chosen: a commercial sample LUVICAN (BASF) and a cationically polymerized one. Both samples were fractionated and characterized by GPC and viscometry. The first ones were treated with a sulphuric acid‐nitric acid mixture, while the second ones were nitrated in presence of dimethyl sulphoxide. The glass transition temperature and the corresponding dielectric α relaxation were studied by differential scanning calorimetry and thermally stimulated currents techniques, respectively. Rigidity of the macromolecular chain and the degree of nitration lead to different behaviour in the relaxation process.
EPR parameters of radical ions and polarizability effect
Authors: Egorochkin Alexey N. , Kuznetsova Olga V. , Khamaletdinova Nadiya M. , Domratcheva‐Lvova Lada G. 
Published: March 2011

AbstractThe literature data on substituent influence on the g factors, hyperfine coupling (hfc) constants (a) of the EPR signals and the spin densities (ρ) have been analyzed for 25 series of the organic radical cations and radical anions as well as of the transition metal complexes. The g, a, and ρ values were first established to depend not only on the inductive and resonance effects but also on the polarizability of substituents which can be characterized by the σα constants. The polarizability effect is caused by the partial charge on the radical center. This effect consists in an electrostatic attraction between the charge and the dipole moments induced by this charge in the substituents. The polarizability contribution ranges up to 92%. Copyright © 2011 John Wiley & Sons, Ltd.
Experimental and computational studies of nJ(77Se,1H) selenium–proton couplings in selenoglycosides
Authors: Kövér Katalin E. , Kumar Ambati Ashok , Rusakov Yury Yu. , Krivdin Leonid B. , Illyés Tünde‐Zita , Szilágyi László 
Published: March 2011

AbstractSelenoglycosides are important starting materials in synthetic carbohydrate chemistry and play a role in biological interactions as well. Both aspects are influenced by the conformation around the glycosidic bond. Here, we present a combined experimental and computational approach to measure and evaluate nJ(77Se,1H) coupling constants for their use in conformational analysis. The measurements were carried out using a modified CPMG‐HSQMBC pulse scheme which yields pure absorption antiphase multiplets to allow accurate determination of the nJXH values regardless of the size of the proton‐proton couplings. Theoretical calculations were performed at the Second‐Order Polarization Propagator Approach (SOPPA) level. Population‐averaged values calculated for geminal and vicinal couplings are in a good agreement with experiment indicating an adequate theoretical level of the calculations. Experimental observations and computations alike have indicated that two‐bond 77Se‐1H couplings, 2J(77Se,1H), in a H1‐C1‐Se‐X moiety are very sensitive to the torsion angle around the C1‐Se‐bond and will, therefore, be useful for conformational studies. Copyright © 2011 John Wiley & Sons, Ltd.
Resolution of a nonionic surfactant oligomeric mixture by means of DOSY with inverse micelle assistance
Authors: Asaro Fioretta , Savko Nina 
Published: March 2011

AbstractDOSY is a recognized, efficient technique in the analysis of mixtures. It relies on the differences in self‐diffusion coefficients, which are determined by the molecular size. Nowadays, efforts are directed towards devising matrices able to interact with the components of the mixture with differential affinity, and therefore capable to interfere with the diffusion processes and to display resolving power towards species of close, or even equal molecular weight, like isomers. Usually, commercial nonionic surfactants are mixtures of oligomeric species, since the head group, which is a short polyoxyehtylene chain, is somewhat polydisperse. The embedment of Igepal CA‐520, 5 polyoxyethylene iso‐octylphenyl ether, in an inverse microemulsion led to the separation of 1H signals of the various oligomeric components. This ensued from the differential partitioning between the oil and the surface of the inverse micelles, which depends on the ethyleneoxide number (EON) of the head groups. Thus, it was possible to ascertain that the length distribution of the polyethyleneoxide chains is ingood agreement with the Poisson distribution theoretically predicted for the polymerization of ethylene oxide. The DOSY spectrum contributed to the assignment of the signals and afforded the partition degree, between the two environments, for each individual oligomeric species, providing further insight into nonionic inverse microemulsions, at present widely employed reaction media in the nanotechnological syntheses. Copyright © 2011 John Wiley & Sons, Ltd.
Rapid acquisition of 1H and 19F NMR experiments for direct and competition ligand‐based screening
Authors: Dalvit Claudio , Gossert Alvar D. , Coutant Jérôme , Piotto Martial 
Published: March 2011

AbstractDirect and competition ligand‐based NMR experiments are often used in the screening of chemical fragment libraries against a protein target due to the high relative sensitivity of NMR for protein‐binding events. A plethora of NMR methods has been proposed for this purpose. Two of these techniques are the 19F T2 filter and the 1H selective T2 filter experiments. Modifications of the pulse sequences of these experiments have resulted in a ∼2‐fold reduction in the experiment time thus allowing an increase in the screening throughput and making NMR an attractive technique for screening large compound collections. Copyright © 2011 John Wiley & Sons, Ltd.
Dynamic 1H NMR study around the carbon–carbon single bond and partial carbon–carbon double bond in the two particular phosphorus ylides and in an enaminoester
Authors: Habibi‐Khorassani Sayyed Mostafa , Ebrahimi Ali , Maghsoodlou Malek Taher , Same‐Salari Sara , Nasiri Shahin , Ghasempour Hojjat 
Published: March 2011

AbstractHerein, a series of separate dynamic 1H NMR effects are reported at different temperatures within a particular enaminoester involving a phenanthridine. These effects are attributed to restricted rotation around the two single bonds such as carbon–carbon (HaCCHb) and nitrogen–carbon (NCCOOCH3). Activation energies (Ea) for these interconversion processes in their rotational isomers are equal to 20 and 20 ± 1 kJ mol−1, respectively. In addition, three dynamic 1H NMR effects are investigated at different temperatures for a particular phosphorus ylide involving a 2‐indolinone around the carbon–carbon single bond (HCCPPh3) within the two Z‐ and E‐rotational isomers and partial carbon–carbon double bond (OCH3‐CC‐PPh3). Activation energies (Ea) for these interconversion processes in rotational isomers are equal to 53, 63 and 73 ± 1 kJ mol−1, respectively. This behavior was also observed for other phosphorus ylide containing 2‐mercaptobenzoxazole around the carbon–carbon single bond and partial carbon–carbon double bond with their relevant activation energies containing 13, 10 and 75 ± 1 kJ mol−1, respectively. Copyright © 2011 John Wiley & Sons, Ltd.
Application of fluorine NMR for structure identification of steroids
Authors: Ampt Kirsten A. M. , Aspers Ruud L. E. G. , Jaeger Martin , Geutjes Pepijn E. T. J. , Honing Maarten , Wijmenga Sybren S. 
Published: March 2011

AbstractFluorinated steroids were examined using 1D and 2D homo‐ and heteronuclear 19F NMR, such as 19F1H and 19F13C. The utilization of fluorine NMR accounted for spectral simplification and resulted in a straightforward pathway for the determination of structures including the configuration of these compounds; these steroids present an illustrative example for other types of fluorinated compounds, which are increasingly encountered in drug discovery. The potential of 19F NMR is elaborated on in detail for two compounds containing diastereotopic fluorines with different coupling patterns. The analysis of the coupling patterns and the through‐space interactions resulted in the determination of the structure and configuration. Heteronuclear correlation experiments, i.e. 19F1H HETCOR, 19F13C HMQC and HMBC, and 19F1H HOESY, were applied to determine first the relative stereochemistry and then the molecular configuration at C4 and C5 of a steroidal compound bearing a fused three‐membered ring with two fluorine substituents. These examples proved 19F NMR to be a useful addition to the extensively used 1H and 13C NMR within structure elucidation and configuration determination of small molecules. Copyright © 2011 John Wiley & Sons, Ltd.
From CCSD(T)/aug‐cc‐pVTZ‐J to CCSD(T) complete basis set limit isotropic nuclear magnetic shieldings via affordable DFT/CBS calculations
Authors: Kupka Teobald , Stachów Michał , Nieradka Marzena , Kaminsky Jakub , Pluta Tadeusz , Sauer Stephan P. A. 
Published: March 2011

AbstractIt is shown that a linear correlation exists between nuclear shielding constants for nine small inorganic and organic molecules (N2, CO, CO2, NH3, CH4, C2H2, C2H4, C2H6 and C6H6) calculated with 47 methods (42 DFT methods, RHF, MP2, SOPPA, SOPPA(CCSD), CCSD(T)) and the aug‐cc‐pVTZ‐J basis set and corresponding complete basis set results, estimated from calculations with the family of polarization‐consistent pcS‐n basis sets. This implies that the remaining basis set error of the aug‐cc‐pVTZ‐J basis set is very similar in DFT and CCSD(T) calculations. As the aug‐cc‐pVTZ‐J basis set is significantly smaller, CCSD(T)/aug‐cc‐pVTZ‐J calculations allow in combination with affordable DFT/pcS‐n complete basis set calculations the prediction of nuclear shieldings at the CCSD(T) level of nearly similar accuracy as those, obtained by fitting results obtained from computationally demanding pcS‐n calculations at the CCSD(T) limit. A significant saving of computational efforts can thus be achieved by scaling inexpensive CCSD(T)/aug‐cc‐pVTZ‐J calculations of nuclear isotropic shieldings with affordable DFT complete basis set limit corrections. Copyright © 2011 John Wiley & Sons, Ltd.
On the mechanisms enabling myocardial edema contrast in bSSFP‐based imaging approaches
Authors: Zhou Xiangzhi , Rundell Veronica , Liu Ying , Tang Richard , Shah Saurabh , Zuehlsdorff Sven , Li Debiao , Dharmakumar Rohan 
Published: March 2011

AbstractThe biophysical mechanisms influencing balanced steady‐state free precession (bSSFP) based edema imaging in the setting of acute myocardial infarction are not well understood. To assess the various mechanisms that enable the detection of myocardial edema on bSSFP‐based imaging approaches (cine bSSFP and T2‐prepared bSSFP), experiments were conducted in canine models subjected to ischemia‐reperfusion injury. Results showed that in addition to relaxation effects, the alteration in thermal equilibrium (M0) (including magnetization transfer) has a significant contribution to the image contrast between edematous and healthy myocardium. The relative signal‐intensity ratios between edematous and healthy myocardium were: 1.51 ± 0.18 (cine bSSFP) and 1.58 ± 0.20 (T2‐prepared bSSFP); the theoretically estimated relative relaxation and M0 effects were: 1.17 ± 0.09 and 1.30 ± 0.19, respectively (cine bSSFP), and 1.49 ± 0.23 and 1.06 ± 0.07, respectively (T2‐prepared bSSFP). There were no significant difference between cine bSSFP and T2‐prep bSSFP relative signal‐intensity ratios. However, the relative relaxation effect in cine bSSFP was significantly lower than in T2‐prep bSSFP (P < 0.05), and the M0 effect in cine bSSFP was significantly higher than in T2‐prep bSSFP (P < 0.05). Hence the acquisition strategies that wish to maximize myocardial edema contrast in cine bSSFP imaging should take both relaxation and M0 effects into account. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.