bluuebunny/crossref_metadata_2025_split huggingface dataset:
Homogeneous Phase Polymerization of Vinylidene Fluoride in Supercritical CO2: Surfactant Free Synthesis and Kinetics
Authors: Beuermann Sabine , Imran‐ul‐haq M. 
Published: December 2007

AbstractSummary: Vinylidene fluoride (VDF) polymerizations were carried out in homogeneous phase with supercritical carbon dioxide (scCO2) at 120 °C and 1500 bar. To control molecular weight perfluorohexyl iodide was used. Molecular weight analysis by size‐exclusion chromatography indicates that polymers of low polydispersities ranging from 1.5 to 1.2 at the highest iodide concentration of 0.25 mol · L−1 were obtained. In addition, polymer molecular weight increases linearly with reaction time, indicating that living conditions were established. The “livingness” is based on the labile C‐I bond. The weakness of the C‐I bond is associated with a fast decomposition of the original hexyl iodide, thus, contributing to initiation and to a significant increase in the initiation rate in the initial phase of the polymerization.
Phase‐Equilibrium Measurements of the Polystyrene/Styrene/Carbon Dioxide Ternary System at Elevated Pressures Using ATR‐FTIR Spectroscopy
Authors: Görnert Michael , Sadowski Gabriele 
Published: December 2007

AbstractSummary: In this paper a novel ATR‐IR spectroscopic setup for phase‐equilibrium studies of polymer systems in supercritical carbon dioxide is presented. A calibration procedure for the spectroscopic investigations has been developed and verified. The results of isothermal phase‐equilibrium measurements of the polystyrene/styrene/carbon dioxide ternary system are presented and compared to results of well‐established cloud‐point measurements. The phase behaviour was determined at 338.15 K, at two pressures (10 MPa and 15 MPa), and for two polystyrene samples having different molecular weights (6 kg/mol, 105 kg/mol) and narrow molecular‐weight distributions.
Modeling the Chain‐Length Differentiated Polymer Microstructure of α‐Olefins
Authors: Busch Markus , Becker Katrin 
Published: December 2007

AbstractSummary: Due to a complex polymerization scheme, incorporating besides propagation, termination and transfer to monomer and chain transfer agents in addition intra‐ and inter‐molecular transfer to polymer as well as β‐scission, α‐olefin (co)polymers feature a quite complex polymeric microstructure. It is demanding to design a kinetic model that describes these in a predictive manner in order to have a tool for computer‐aided product design. The molecular weight distribution and branching indices together with the composition are the subjects of interest in this case. The latter quantities are often provided as being averaged over the molecular weight distribution. Modern coupled analytical techniques of size exclusion chromatography provide even more insight. The combination of size exclusion chromatography with fractionation techniques provide under adequate processing of the data branching indices and co‐polymer composition differentiated with respect to chain‐lengths. This contribution will inspect how good a model for predicting the chain‐length differentiated co‐polymer composition in high‐pressure high‐temperature ethene – vinyl acetate‐co‐polymerizations will coincide with analytical results of technical products.
A Study of L‐Lactide Ring‐Opening Polymerization Kinetics
Authors: Puaux Jean‐Pierre , Banu Ionut , Nagy Iosif , Bozga Grigore 
Published: December 2007

AbstractSummary: The paper presents an experimental study of L‐lactide polymerization in molten state using as initiator the Stannous Octoate. The experiments were performed in a Haake mixer. The operating temperatures were between 170 and 195°C, the reaction time up to 60 min and monomer to initiator initial molecular ratio between 102 and 5 · 103. The conversion was determined by using 1H NMR and the molecular weights distributions by SEC. A preliminary mathematical modeling study was also performed, based on experimental data and a previously published reaction scheme.
Ab Initio Calculation of the Propagation Kinetics in Free Radical Polymerization: Chain Length and Penultimate Effects
Authors: Moscatelli Davide , Dossi Marco , Cavallotti Carlo , Storti Giuseppe 
Published: December 2007

AbstractSummary: In this work, Quantum Chemistry is applied to investigate the propagation kinetics in free radical polymerization. Energies, structures and transition state geometries are determined using density functional theory, which combines good accuracy with reasonable computational demand. In particular, B3LYP functional is used to evaluate the exchange and correlation energy with the 6‐311+G(d,p) basis sets. The capabilities of the approach with respect to the prediction of the kinetic constants of elementary processes relevant to polymeric systems (propagation reactions) is first tested using literature experimental data as reference values.1 Namely, two different monomers of industrial relevance have been selected, acrylonitrile and styrene. For such systems, the effect of chain‐length on the propagation rate coefficient is examined. Finally, for the selected monomer pair, the relative reactivity (so‐called reactivity ratios) is also analyzed, in particular considering the penultimate effect.
Temperature and pH Dependency of Copolymerization Parameters of Acrylic Acid and 2‐Hydroxypropyl Acrylate
Authors: Blaszk Christoph , Grünitz Jan , Möller Maike , Pauer Werner , Moritz Hans‐Ulrich , Schwede Christian 
Published: December 2007

AbstractSummary: Since copolymerization parameters of acrylic acid (AA) and 2‐hydroxypropyl acrylate (HPA) in aqueous solutions are scarcely investigated a new method and different experimental setups were developed to run copolymerization experiments at different temperatures and pH values. The experiments were done with UV‐ or azo‐ initiation and analyzed by residual monomer analytics with HPLC and GPC methods. Based on the data obtained the conversion and copolymerization parameters were calculated with different mathematical models.
Reaction Inhibition as a Method for Preventing Thermal Runaway in Industrial Processes
Authors: Russo Alessandra , Maschio Giuseppe , Ampelli Claudio 
Published: December 2007

AbstractSummary: In this work inhibitors were used to prevent runaway reactions during methylmethacrylate suspension polymerization processes. The main problem that may more frequently occur in chemical reactors, carrying out free radical polymerization reactions, is the loss of temperature control. The addition of an inhibitor during polymerization processes can be considered as a good method to stop or at the least slow down the reaction. In this work two inhibitors were used: hydroquinone and 1,4‐benzoquinone in a series of polymerization experiments. In order to identify situations that can lead to a runaway reaction, an early warning detection system based on the divergence criterion was used. When this system signalled an alarm, small amounts of inhibitor were added to the reaction mixture. The results showed that hydroquinone and 1,4‐benzoquinone behave slightly differently and the reactor temperature can be kept within safe limits.
Advanced Calorimetric Techniques in Polymer Engineering
Authors: Grolier Jean‐Pierre E. , Dan Florin 
Published: December 2007

AbstractSummary: In polymer synthesis, reaction calorimetry (RC) is an appropriate technique for on‐line process monitoring, since polymerization reactions are highly exothermic. Measurements are noninvasive, rapid, and straightforward. Nowadays RC is the technique recognized as the most powerful way to study such process in near‐to‐the‐ industrial conditions. Our approach was focused on temperature oscillation calorimetry (TOC). Two different reaction calorimeters were used, i.e. a isoperibolic calorimeter and a Calvet type high sensitivity differential calorimeter, respectively. A special attention was paid to the interpretation of the measured signals in order to obtain reliable calorimetric data. The evolution of heat transfer coefficient UA was followed by performing appropriate Joule effect calibrations, before and after the reaction. A convolution differential method of the measured heat flow by the generated one was used for determining the time constants and deconvoluting the measured heat flow.
Online‐Analysis on Acoustically Levitated Droplets
Authors: Biedasek Silke , Abboud Mohammed , Moritz Hans‐Ulrich , Stammer Achim 
Published: December 2007

AbstractSummary: Aqueous solutions of acrylic acid were levitated in a 40 kHz acoustic levitator. The monomer amount in the levitated droplets was monitored by Raman spectroscopy relating to an internal standard. Thus evaporation of the monomer as well as polymerization reactions initiated by a redox system were investigated by Raman spectroscopy and resultant data were compared to HPLC data. Decreases in monomer amount due to evaporation can be clearly distinguished from polymerization reactions. Additionally, temperature measurement within the droplet throughout a polymerization reaction shows the typical temperature course originating from the heat of polymerization.
What Kind of Image is Drawn by a MALDI‐Experiment of Grafted Nanoparticles? ‐ How to Distinguish between Chemically and Physically Adsorbed Parts
Authors: Dempwolf Wibke , Nothdurft Lars , Schmidt‐Naake Gudrun 
Published: December 2007

AbstractSummary: The modern MALDI‐TOF mass spectrometry is a powerful technique for the fast and accurate determination of a number of polymer characteristics like end group analysis. It can also be used to analyze the grafted shell around silane modified nanoparticles. This shell contains physically and chemically adsorbed parts. It is a question of great interest what kind of adsorbent can be visualized by using MALDI‐TOF mass spectrometry, while it is not possible to ionize the whole AEROSIL® particle. Therefore we chose the system MPTMS/AEROSIL®200 to address this issue. We grafted AEROSIL®200 with methacryloxy(propyl)‐trimethoxysilane (MPTMS) under acid conditions. The grafted nanoparticles were treated via Soxhlet extraction. The resulting fractions (the washed nanoparticles and the Soxhlet extract) were systematically analyzed by using MALDI‐TOF MS as well as the grafted nanoparticles themselves. As a crosscheck MPTMS was homopolymerized and analyzed. Our results show that for the system under investigation there is strong evidence that only the physically adsorbed part can be analyzed via MALDI‐TOF MS.
Cued task‐specific training is better than exercise in improving sit‐to‐stand in patients with Parkinson's disease: A randomized controlled trial
Authors: Mak Margaret K.Y. , Hui‐Chan Christina W.Y. 
Published: December 2007

AbstractWe examined whether 4 weeks of audio‐visual (AV) cued task‐specific training could enhance sit‐to‐stand (STS) and whether the treatment effects could outlast the treatment period by 2 weeks. Fifty‐two subjects with PD completed the study. They were randomly allocated to receive 4 weeks of AV cued task‐specific training, conventional exercise (Ex), or no treatment (control). Each subject was assessed before, at the end of 2 and 4 weeks of treatment, and 2 weeks after treatment ended. After 2 weeks of training, the AV group significantly increased the peak horizontal velocity (by 13%, P<0.01) when compared with the Ex group. After 4 weeks of training, AV group increased both peak horizontal and vertical velocities, respectively by 18% and 51%, and reduced the time taken to complete STS by 25%. These improvements were greater than those of the Ex group, who showed 8% (nonsignificant between‐group) and 20% (P<0.05 between‐group) increases respectively for peak horizontal and vertical velocities, and 10% decrease in movement time (P<0.05). Worth‐noting is the improvements in AV group could be carried over to 2 weeks after treatment ended. These findings provided concrete evidence for the use of AV cued task‐specific training to reeducate STS in patients with PD. © 2007 Movement Disorder Society
Novel biomimetic composite based on collagen and poly(γ‐benzyl L‐glutamate)‐co‐poly(glutamic acid)
Authors: Zhou Xiumiao , Wang Yingjun , Ren Li , Wang Lingyun 
Published: December 2007

AbstractNovel biomimetic composite was prepared by the reaction of collagen and poly(γ‐benzyl L‐glutamate)‐co‐poly(glutamic acid) (PBLG‐co‐PGA), which were crosslinked by non‐toxic crosslinking reagents 1‐ethyl‐(dimethylaminopropyl) carbodiimide (EDC) and N‐hydroxysuccinimide (NHS). The composite was characterized by FTIR and DSC. FTIR results confirmed that the collagen in the composite was successfully crosslinked with PBLG‐co‐PGA. DSC results showed that the composites possessed higher shrinkage temperature and higher thermal stability than the collagen. The water absorption test showed that the water absorbency of the composites increased with the increase in PBLG‐co‐PGA content in the composite. The studies of collagenase degradation and the tensile strength showed that the biostability and the tensile strength of the composites were significantly improved in comparison with that of the collagen. According to the investigations of cell adherent ratio and cell proliferation in vitro, the composite possessed good biocompatibility. Copyright © 2007 John Wiley & Sons, Ltd.
Theoretical prediction of linear free energy relationships using proton nucleomers
Authors: Macchia Giovanni La , Gagliardi Laura , Carlson Geoffrey S. , Jay Ashley N. , Davis Erik , Cramer Christopher J. 
Published: December 2007

AbstractValues of σ and σ+, for use in linear free energy relationships, are determined for para hydrogen atoms having nuclear charges other than 1 (nucleomers). Hammett ρ values for a variety of free energies of activation, reaction, and other extrathermodynamic properties (e.g., vibrational frequencies) are computed therefrom and compared to those computed using typical para functional groups. The nucleomer correlations show excellent qualitative agreement with standard correlations but the quantitative agreement is less good, typically underestimating the standard ρ‐value by 10–60%. Copyright © 2007 John Wiley & Sons, Ltd.
Synthesis and Characterization of First Generation Dendritic Azidoesters
Authors: Pant Chandra Shekhar , Wagh Rashmi M. , Nair Jaya K. , Gore Girish M. , Thekkekara Mukundan , Venugopalan Sethuramasharma 
Published: December 2007

AbstractA new class of first generation azido‐terminated dendritic esters have been synthesized by four step processes. The final products and the intermediates are characterized by IR, 1H NMR, and elemental analysis. Thermal studies revealed that these dendritic esters were thermally stable up to ∼190 °C and the glass transition temperature was found to be −54 and −32 °C, respectively.
Studies of Free Field and Confined Explosions of Aluminium Enriched RDX Compositions
Authors: Trzciński Waldemar A. , Cudziło Stanisław , Paszula Józef 
Published: December 2007

AbstractResearch on the effect of aluminium contents and its particle size on free field and confined explosions characteristics of RDX‐based compositions containing 15–60% aluminium was carried out. Parameters of blast waves produced by charges of the investigated explosives detonating in an open space were measured by the use of piezoelectric gauges. Simultaneously, photodiode set‐ups were used to measure light output of the detonating charges. Quasi‐static pressure measurements were conducted in steel chambers of 0.15 and 7 m3 volume filled with air. Moreover, the heat of detonation was measured with a calorimetric set in a 5.6 dm3 bomb filled with argon. The results of QSP and detonation heat measurements were compared with those obtained from thermochemical calculations.
Study of Confined Pyrotechnic Compositions for Medium/Large Calibre Gun Igniter Applications
Authors: Gransden Joseph I. , Taylor Michael J. 
Published: December 2007

AbstractWith the continued shift towards more insensitive munitions and the subsequent development of low vulnerability propellants, the study of novel gun igniters is playing a significant role in the design of future direct and in‐direct fire charge systems. Previously, concepts such as electrothermal plasma ignition have offered high performance ignition solutions. However, using current technology they lack practical, in‐service applicability and will be difficult to incorporate into near future combat systems at a low cost.
Live‐cell analysis of cell penetration ability and toxicity of oligo‐arginines
Authors: Tünnemann Gisela , Ter‐Avetisyan Gohar , Martin Robert M. , Stöckl Martin , Herrmann Andreas , Cardoso M. Cristina 
Published: December 2007

AbstractCell penetrating peptides (CPPs) are useful tools to deliver low‐molecular‐weight cargoes into cells; however, their mode of uptake is still controversial. The most efficient CPPs belong to the group of arginine‐rich peptides, but a systematic assessment of their potential toxicity is lacking. In this study we combined data on the membrane translocation abilities of oligo‐arginines in living cells as a function of their chain length, concentration, stability and toxicity. Using confocal microscopy analysis of living cells we evaluated the transduction frequency of the L‐isoforms of oligo‐arginines and lysines and then monitored their associated toxicity by concomitant addition of propidium iodide. Whereas lysines showed virtually no transduction, the transduction ability of arginines increased with the number of consecutive residues and the peptide concentration, with L‐R9 and L‐R10 performing overall best. We further compared the L‐ and D‐R9 isomers and found that the D‐isoform always showed a higher transduction as compared to the L‐counterpart in all cell types. Notably, the transduction difference between D‐ and L‐forms was highly variable between cell types, emphasizing the need for protease‐resistant peptides as vectors for drug delivery. Real‐time kinetic analysis of the D‐ and L‐isomers applied simultaneously to the cells revealed a much faster transduction for the D‐variant. The latter underlies the fact that the isomers do not mix, and penetration of one peptide does not perturb the membrane in a way that gives access to the other peptide. Finally, we performed short‐ and long‐term cell viability and cell cycle progression analyses with the protease‐resistant D‐R9. Altogether, our results identified concentration windows with low toxicity and high transduction efficiency, resulting in fully bioavailable intracellular peptides. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd.
Membrane‐bound peptides from V‐ATPase subunit a do not interact with an indole‐type inhibitor
Authors: Hesselink Renske W. , Fedorov Alexander , Hemminga Marcus A. , Prieto Manuel 
Published: December 2007

AbstractThe V‐ATPases are ATP‐dependent proton pumps, found in virtually all cells, responsible for acidification of organelles and energizing of plasma membranes. Its role in diseases, such as osteoporosis and metastatic cancer, makes the V‐ATPase a potential drug target. Short synthetic peptides that are presented here mimic the 7th transmembrane domain (TM7) of subunit a (Vph1p) of Saccharomyces cerevisiae V‐ATPase, an essential part of the membrane‐bound VO domain, where proton translocation takes place. The peptides adopt a transmembrane configuration only in membranes containing anionic lipids, stressing the importance of strong interfacial anchoring by the flanking lysines. Peptide P1, which contains the essential arginine R735, is monomeric, whereas peptide P2, which lacks this extra charge, tends to aggregate in the membrane. SB 242784, which is a highly potent inhibitor of V‐ATPase, does not show any interaction with the peptides, indicating that TM7 alone is not sufficient for inhibitor binding. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd.
Mass spectrometric characterization of β‐caryophyllene ozonolysis products in the aerosol studied using an electrospray triple quadrupole and time‐of‐flight analyzer hybrid system and density functional theory
Authors: Kanawati Basem , Herrmann Frank , Joniec Seweryn , Winterhalter Richard , Moortgat Geert K. 
Published: December 2007

AbstractThe components of the organic aerosol formed due to gas‐phase β‐caryophyllene ozonolysis were characterized by the use of a triple quadrupole and time‐of‐flight analyzer hybrid system coupled to an electrospray ionization source operated in the negative ion mode. A reversed‐phase high‐performance liquid chromatography (HPLC) column was used to achieve chromatographic separations at neutral pH which has been proved to induce ionization of organic compounds bearing aldehyde moieties. In addition to the detected oxo‐ and dicarboxylic acids, isomeric oxidation products, which bear multi‐functional groups such as aldehyde, carbonyl and hydroxyl groups, could be differentiated by examining their corresponding collision‐induced dissociation (CID) fragmentation pathways. Proposed fragmentation mechanisms were drawn for the experimentally observed fragmentation pathways in all the CID experiments. Cyclic oxidation products could also be discerned and their fragmentation behaviour under low energy collsional conditions was studied in detail. Gas‐phase deprotonation potentials were calculated by the use of DFT B3LYP/6‐311+G(2d,p)//B3LYP/6‐31+G(d) + ZPVE to estimate the most thermodynamically favourable deprotonation site for efficient negative ion formation in the ion source. The optimized gas‐phase geometries for the most prominent oxidation products reveal a strong intramolecular interaction between the upper and lower C4 carbon chains, which are formed after the decomposition of the primary ozonide generated by ozone attack of the reactive endocyclic CC bond. Copyright © 2007 John Wiley & Sons, Ltd.
Confidence intervals for the risk ratio under inverse sampling
Authors: Tian M. , Tang M. L. , Ng H. K. T. , Chan P. S. 
Published: December 2007

AbstractIn this paper, we investigate various confidence intervals for the risk ratio under inverse sampling (also known as negative binomial sampling). Three existing confidence intervals (namely, the confidence intervals that are based on Fieller's theorem, the delta method and theF‐statistic) are reviewed and three new confidence intervals (namely, the score, likelihood ratio and saddlepoint approximation (SA)‐based confidence intervals) are developed. Comparative studies among these confidence intervals through Monte Carlo simulations are evaluated in terms of their coverage probabilities and expected interval widths under different settings. Our simulation results suggest that the SA‐based confidence interval is generally more appealing. We illustrate these confidence interval construction methods with real data sets from a drug comparison study and a congenital heart disease study. Copyright © 2007 John Wiley & Sons, Ltd.