bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization by Raman microspectrometry of residual compressive stresses induced by resin curing in single filament composite samples
Authors: Masse P. , Cavrot J. P. , Depecker C. , Laureyns J. , Escaig B. 
Published: March 2011

AbstractThe present work concerns monofilament composite samples used in the pull‐out test to quantify the effect of different fibre surface treatments on the adhesion of a high modulus polyethylene in a polyester resin. Optical observations revealed local deformations induced by a compressive stress generated in the fibre by the resin shrinkage during the curing. The sensitivity of the polyethylene Raman peak at 1130 cm−1 to elastic strain has been used to characterize the local compression state still present in the fibre after the curing. The results show residual stresses varying along the fibre embedded length up to a level depending on the applied surface treatment i.e. on the degree of adhesion between the fibre and the resin. This is consistent with the localization and the morphologies of shear bands observed in the samples. More the Raman microspectrometry has been used to determine the tensile stress profile along the embedded part of the fibre when its free part is stretched. Corrected of the initial compression state this profile represents the stress transfer effectively realized from the fibre to the resin for different adhesion conditions. Its knowledge is very useful to clarify the interface damage and pull‐out mechanisms.
Spectral biodiagnostics of tissues with fiber optics
Authors: Afanasyeva N. , Artjushenko V. , Lerman A. , Plotnichenko V. , Frank G. , Neuberger W. 
Published: March 2011

AbstractThe synergy of novel MIR‐fibers with FTIR‐spectroscopy opens a new horizon in applications of spectroscopy in 4 − 16 μm range in vivo medical diagnostics. The innovated bare core and core‐clad MIR‐fibers are produced by hot extrusion method from the crystals of silver halides solid solutions. These non‐toxic and non‐hygroscopic fibers are characterized by low optical losses: 0.1 − 0.5 dB/m nearby 10μm, and high flexibility: Rbending > 10–100 fiber diameters. Some prototypes of accessories for FTIR‐spectrometers, based on commercially available MIR‐fibers for several areas of promising applications are developed. Non‐invasive medical diagnostics in vivo: cancer detection and glucose content measurements in whole human blood is possible. The new family of evanescent fiber sensors is started for the direct in‐process applications. Fiberoptic Evanescent Wave FTIR Spectroscopy (FEWS) for cancer diagnosis in human organs is exemplified in this paper, and their great potentiality is demonstrated.
Counterion effects in the anionic polymerization of methyl methacrylate: Mechanistic relevance to GTP
Authors: Warmkessel Jeffrey , Kim Jungsoo , Quirk Roderic P. , Brittain William J. 
Published: March 2011

AbstractThe room temperature polymerization of methyl methacrylate (MMA) by the cesium or tetrabutylammonium salt of 9‐methylfluorenide proceeds in an uncontrolled fashion. To understand these results, we have studied the structure of the propagating chain‐ends using polymer microstructure and stopped‐flow FT‐IR spectroscopy of model compounds. Deprotonation of methyl isobutyrate with the cesium salt of 1,1,4,4‐tetraphenylbutane dianion afforded the corresponding cesium enolate (U=1645 cm−1). The deprotonation of methyl 2,2,4‐trimethyl‐4,6‐dicarbomethoxyhept‐6‐en‐1‐oate (the trimeric ester of MMA) was accompanied by a rapid (2–4 s) intramolecular cyclization. Comparison of group transfer polymerization (GTP) to anionic polymerization reveals that the counterion is important but probably not the sole mechanistic feature responsible for the living behavior of GTP.
Multi‐arm star polyisobutylenes: 2. The effect of synthesis conditions on the structure of star PIBs
Authors: Marsalkó Timea M. , Majoros István , Kennedy Joseph P. 
Published: March 2011

AbstractMulti‐arm star polyisobutylenes (*‐(PIB)n) have been prepared by the “arm‐first” method. This synthesis was accomplished by adding various linking agents (“core builders”) such as p‐ and m‐divinylbenzene (DVB) and p‐ and m‐diisopropenylbenzene (DIB) to living PIB® charges and thus obtaining a crosslinked aromatic core holding together a corona of well‐defined arms. The products were characterized in terms of overall arm/core composition, molecular weight, and molecular weight distribution (M̄w/Mn). The effect of reaction conditions (time, [linking agent]/[PIB], arm molecular weight) on the kinetics of the star formation and star structure were investigated. The multi‐arm star nature of *‐(PIB)ns was proven directly by determining the molecular weight (by light scattering) of the intact products, selectively destroying the aromatic polyDVB (or polyDIB) core (“core‐destruction”), and finally determining the molecular weight of the surviving aliphatic PIB arms. The synthetic strategy, overall kinetics, and observations during the preparation of star‐PIBs were discussed. Among the critical parameters that determine product structures are the rate of crossover PIB⊕ + DVB (or DIB) → PIB‐DVB⊕ (or PIB‐DIB⊕), the concentration of the linking agent DVB (or DIB), and the molecular weight of the PIB arm. Evidence for the formation of higher order stars (“secondary”, etc.) by star‐star‐ coupling has been presented.
Kinetic study of the living cationic polymerization of isobutylene using t‐Bu‐m‐DCC/TICL4/2,4‐dimethylpyridine initiating system
Authors: Storey Robson F. , Choate Kim R. 
Published: March 2011

AbstractKinetics of the living cationic polymerization of isobutylene, initiated by the system t‐bu‐m‐DCC/TiCl4/2,4‐dimethylpyridine (2,4‐DMP), were studied as a function of concentration of the various components of the initiation system, solvent polarity, and presence of the protic acid scavenger, 2,6‐di‐tert‐butylpyridine (DTBP). Under a variety of conditions, the effective number of growing chains in a given polymerization remained constant and Mn increased linearly with monomer conversion. The system was found to yield an essentially homogeneous reaction mixture in hexanes/methyl chloride cosolvents, with only a small amount of precipitate, probably 2,4‐dimethylpyridinium salts resulting from proton scavenging by the tertiary amine. It was found that increasing [TiCl4] strongly increased the rate while increasing [2,4‐DMP] weakly decreased the rate. Evidence of a retardation of the polymerization rate by the soluble TiCl4:2,4‐DMP complex was observed. The addition of DTBP as a protic acid scavenger, with or without 2,4‐DMP, very weakly decreased the rate of polymerization. Increasing the fraction of methyl chloride in the solvent mixture caused an increase in the rate of polymerization. All of the results were consistent with a propagation mechanism in which an equilibrium exists between dormant and ionized, active chain ends.
Living and stereoselective polymerization of [2.2]‐paracyclophan‐2‐ENE derivatives
Authors: Miao Yi‐Jun , Sun Benjamin J. , Bazan Guillermo C. 
Published: March 2011

AbstractParacyclophene based monomers can be polymerized in a living fashion using the alkylidene initiator Mo(NAr)(CHCMe2Ph)(OCMe(CF3)2)2. The cis‐specific nature of the polymerization is critical, since small amounts of trans olefin in the backbone renders the material insoluble. These polymers have complex photophysical behavior, probably a consequence of the close proximity of chromophores along the polymer backbone. Polymerization of 9‐(tert‐butyldimethylsilyloxy)‐[2.2]‐paracyclophan‐1‐ene produces a new precursor material which furnishes PPV under remarkably mild conditions.
Living block copolymerization of phenyl vinyl sulfoxides and characterization of a stereogradient polymer
Authors: Buese Mark A. , Zhang Yingchao 
Published: March 2011

AbstractThe polymerization of phenyl vinyl sulfoxide in blocks of increasing enantiomeric excess was carried out. Portions of the polymer were removed after each charge of monomer was consumed. The poly(phenyl vinyl sulfoxide)s were characterized by gel permeation chromatography and nuclear magnetic resonance spectroscopy. Reduction of the poly(phenyl vinyl sulfoxide)s to poly(phenyl vinyl sulfide)s permitted assignment of the polymer stereochemistry and verification that stereogradient polymers were formed.
Liquid crystal dimers and oligomers: Experiment and theory
Authors: Luckhurst Geoffrey R. 
Published: March 2011

AbstractLiquid crystal dimers and trimers exhibit a range of unusual properties which are fascinating in their own right and which also parallel those found for semi‐flexible main‐chain liquid crystal polymers. This close similarity suggests that dimers and oligomers should form good model systems for their polymeric counterparts and evidence is presented in support of this view. The transitional properties of a range of dimers, all containing the cyanobiphenyl mesogenic group, are presented to illustrate their dependence on the length and parity of the spacer as well as the nature of its link to the mesogenic groups. It is shown that the odd‐even effect thought to characterise dimers docs not always occur and can also vanish when rod‐like mesogens are replaced by disclike groups. Theories, of varying degrees of sophistication, are presented with which to understand the transitional behaviour of the dimers. Of particular interest is a generic model which seems to represent the essential features of the liquid crystallinity of dimers. An especially important characteristic of liquid crystals is their orientational order. The results of NMR studies of this for dimers are described and shown to lead to a novel model of the molecular organisation in the nematic phases of dimers. This simple picture is found to be in accord with the more complete molecular field theories. Finally, the behaviour of liquid crystal trimers is compared with that of dimers, this comparison suggests that much of the essential physics for the polymeric systems is contained within that of the dimers. However, trimers do allow the introduction of novel structural features not possible within dimers. The behaviour of such systems should provide a uniquely valuable test bed for molecular theories of liquid crystal oligomers.
Structure and dynamics of liquid‐crystalline polymers with different molecular architectures
Authors: Spiess H. W. 
Published: March 2011

AbstractThe structure and dynamics of liquid‐crystalline polymers with different molecular architectures as revealed by multidimensional NMR Is described. Specific examples discussed Include semiflexible, rigid‐rod, calamitic, and discotic systems. Structural aspects addressed are the determination of high rank order parameters, the micro‐order in frozen liquid crystals and the packing of flexible side chains. Local dynamics In the glassy state, conformational dynamics and collective phenomena such as the development of convective director structures are discussed. It is demonstrated that advanced NMR spectroscopy yields highly specific information not available from conventional scattering, microscopic and relaxation techniques.
The spatial inhomogeneity of rodlike polymeric systems subject to simple shear flow
Authors: Ding Jiandong , Yang Yuliang 
Published: March 2011

AbstractA novel simulation approach has been developed by the combination of Brownian dynamics and Lebwohl‐Lasher nematogen potential, by which we have made preliminary investigation on the spatial inhomogeneity of nematic rodlike polymeric system with planar surface anchoring and subject to simple shear flow. Some rheological behaviors such as the damped oscillation of stresses with time or the negative first normal stress difference at moderate shear rate find good agreement with previous experimental observations reported in literature. The distribution function of rod orientation takes on “breathe‐like” time‐evolution and is verified not Gaussian‐featured. The layered director, order parameter, shear stress and first normal stress difference have also been calculated by statistics, and most importantly, all of these statistic quantities show spatial distribution in different layers and corresponding distribution functions are time‐dependent. Therefore, our simulation implies the complicated pattern formation and pattern evolution in this system. It is, hence, very meaningful to further study the spatial inhomogeneity of rodlike polymers under shear flow extensively both in theory and in experiment.
Liquid crystalline polymers: From self‐organization to functions and applications
Authors: Anderle Klaus , Wendorff Joachim H. , Chemie Fachbereich Physikalische , Fur Material Wissenschaft Wissenschaftliches Zentrum 
Published: March 2011

AbstractLiquid crystals derive their unusual properties and their broad range of applications from their unique spatial and orientational order giving rise to specific symmetries, to strong anisotropies with respect to macroscopical properties and to a strong coupling to external fields. We have studied for liquid crystalline polymers modes of inducing strong modifications of the anisotropic optical properties locally in solid films by light. A storage process is described in this contribution which is based on light‐induced trans‐cis‐trans‐isomerization reactions of azobenzene chromophores attached to a polymer backbone as side groups in liquid crystalline polymers. The chromophores are able to rotate in the glassy state if subjected to linearly polarized light: the azobenzene units approach a saturation orientation which is perpendicular to the polarization direction of the light. The contribution discusses the molecular mechanism of this process as well as possible applications.
Charge carrier mobilities in liquid crystalline mesomorphic poly(DI‐n‐Alkylsilylene)s; influence of backbone conformation
Authors: van Der Laan Garrelt P. , De Haas Matthijs P. , Frey Holger , Möller Martin 
Published: March 2011

AbstractThe charge transport properties of a series of symmetrically substituted mesomorphic poly(di‐n‐alkylsilylene)s are studied using the pulse‐radiolysis time resolved microwave conductivity (PR‐TRMC) technique. The observed conductivities for these polymers could be correlated with different backbone conformations present both in the crystalline solid phase and in the liquid crystalline mesophase. The transition from the solid phase to the mesophase is accompanied by a disordering of the silicon backbone that results in a decrease of the conductivity of up to two orders of magnitude. The charge carrier mobilities found varied from 5×10−5 m2 /Vs for the all‐trans conformation in the solid phase to 6×10−7 m2 /Vs for the disordered backbone conformation in the mesophase. The anisotropic radiation‐induced conductivity observed for aligned poly(di‐n‐hexylsilylene) samples demonstrate that charge carrier migration takes place preferentially in the direction of the polymer backbone.
The effect of aluminium compounds in the copolymerization of ethylene / α‐olefins
Authors: Katayama Hiroaki , Shiraishi Hiroyuki , Hino Takahiro , Ogane Takuya , Imai Akio 
Published: March 2011

AbstractTwo types of copolymerizations were found with the catalyst system Cp2ZrCl2/MAO. One was a less exothermic reaction, and another was a more exothermic one. The former provided a polymer with a single composition distribution because of a single cationic active site. The latter provided a polymer with a bimodal composition distribution, indicating the existence of two active sites. The two active sites were investigated through the comparison of MAO systems and alkylaluminium / borate systems. We speculated that the two active sites were the normal cationic site and the active site where the interaction between a cationic metallocene and an aluminium compound was strong.
The preparation of aluminoxane from trimethylaluminium at a defined surface of deeply cooled ice
Authors: Winter Hergen , Schnuchel Wolf , Sinn Hansjörg 
Published: March 2011

AbstractThe controlled hydrolysis of trimethylaluminium (TMA) on a defined surface of cooled ice to the corresponding aluminoxanes provides good yields of a toluene soluble product. The reaction was conducted in a specially designed reactor with a rotating scraper. The product properties are independent of reaction temperature between −28 and −40 °C and scraping speed, but can be varied with the extent of hydrolysis.A series of reactors was built for the investigation of this reaction system, the biggest ones producing between 0.5 and 1 kg of aluminoxane solution per day. The safety and ease of use was improved with each subsequent reactor design.
Phase separation of methylalumoxane with diethyl ether
Authors: Hagendorf Wiebke , Harder Annette , Sinn Hansjörg 
Published: March 2011

AbstractAfter the addition of diethylether to a solution of methylalumoxane in toluene, phase separation can be observed. The investigation of several phase separation experiments led to an idea of the possible composition of methylalumoxane that could be consisting of a basic element and differently associated trimethylaluminium.Investigations of the system methylalumoxane–diethylether–trimethylaluminium show that diethylether is stronger complexed at methylalumoxane than with trimethylaluminium. A second model of the structure of methylalumoxane allows an attempt to explain the phenomenum of phase separation.
An approach to phase behaviour in polymers
Authors: Keller A. , Wills H. H. 
Published: March 2011

AbstractAspects of phase transition will be surveyed such as are direct consequences of straightforward thermodynamic considerations yet are not normally taken count of in traditional treatments of phase behaviour even if, as is here shown, they can assume special significance in polymers. The central theme will be the common experience that in most materials, but especially in polymers, the state of ultimate thermodynamic stability is hardly ever attained, consequently that we are dealing with metastable states, the issue of metastability thus becoming the main theme of the present treatise. This metastability can manifest itself either through the phase transformation, even in the thermodynamically stable phase, not reaching completion and/or that phases other than those of ultimate stability appear first often taking on a dominant role. The above two strands are being followed through first separately and finally, with the example of polymer crystallisation, in combination. In the course of it all a variety of phase transformations and numerous potentially intriguing consequences are being touched upon. These are encompassing aspects of liquid‐liquid phase separation, liquid‐crystal formation and crystallisation, the intervention of glass transition, the significance of supercooling, the effect on and influence of the morphology and the connection and interrelation between thermodynamic stability (including metastability) and the rates of the phase transformation, with passing comments on gels and also on some aspects of chain conformation in solution. In the case of the most extensively covered item of crystallisation attention is being drawn to the possibility of stability inversion with phase (here crystal) size. The latter, in terms of ‘Phase Stability Diagrams’, offers a new approach to crystal growth, which in the case of polymers, creates both new perspectives and opens up the possibility of treating so far largely disconnected aspects of the subject within a unifying framework. The survey ends with reference to recent work on amorphisation through pressure pointing to new aspects of material behaviour and to some new and possibly surprising variants of otherwise familiar phase diagrams.
Living polymerization with well‐defined alkylidene catalysts
Authors: Schrock Richard R. 
Published: March 2011

AbstractAlkylidene complexes of the type Mo(CH‐t‐Bu)(NAr)(OR)2 (Ar = 2, 6‐diisopropylphenyl; OR = O‐t‐Bu, OCMe2(CF3), OCMe(CF3)2, etc.) can be prepared from a “universal precursor”, Mo(CH‐t‐Bu)(NAr)(triflate)2(1, 2‐dimethoxyethane),1 which can be prepared in three high‐yield steps from ammonium dimolybdate.2 These complexes serve as initiators for the ring opening metathesis of norbornenes and substituted norbornadienes,3 or for the polymerization of acetylenes to give polyenes,4 all in a living manner. The organic polymer can be cleaved upon treatment with an aldehyde. Norbornenes that contain a variety of organic or inorganic functionalities can be polymerized to give essentially monodisperse homopolymers and block copolymers. Recently chiral catalysts have been prepared that will polymerize norbornenes and norbornadienes stereoselectively to give all cis isotactic polymers.5 Molybdenum catalysts also have been found that will cyclopolymerize dipropargyl derivatives or substituted phenylacetylenes in a living manner.6 The stereospecific synthesis of all cis, or all trans, tactic polynorbornadienes and polynorbornenes will be discussed in detail, including a proof of tacticity.7
New supramolecular architectures based on hydrogen bonding
Authors: Zimmerman Steven C. 
Published: March 2011

AbstractHeterocyclic compounds containing two and three adjacent hydrogen bond donor and acceptor sites in all possible arrangements were synthesized (see generalized structures shown below) to study and use their “base‐pairing” capabilities. With two adjacent donor and acceptor groups there are three possible arrangements and these form two types of complexes (DA·AD and AA·DD). Three adjacent hydrogen bond donor and acceptor sites can be arranged in six different ways and these form three different complexes (ADA·DAD, AAD·DDA, and AAA·DDD).
New industrial fluoropolymer science and technology
Authors: Smart Bruce E. , Feiring Andrew E. , Krespan Carl G. , Yang Zhen‐Yu , Hung Ming‐H. , Resnick Paul R. , Dolbier William R. , Rong Xiao X. 
Published: March 2011

AbstractTeflon® AF, a family of copolymers of perfluoro‐2,2‐dimethyldioxole with tetrafluoroethylene, and Cytop®, a ring‐cyclized homopolymer of CF2=CFO(CF2)2CF=CF2 are the first commercial amorphous perfluoroplastics which combine high optical clarity and solubility with outstanding chemical, thermal and electrical properties. The processes for making these materials are described and recent structure‐property studies that reveal dramatic substituent effects on polymer Tg and related properties are reviewed. The results of some initial fundamental kinetic studies on fluorinated free‐radical cyclizations that relate to efficient cyclopolymerization of fluorinated dienes and the design of new ring‐containing fluoroplastics are discussed.
Influence of cell wall polysaccharides on fruit juice technology
Authors: Will Frank , Dietrich Helmut 
Published: March 2011

AbstractReadily processed clear fruit juices contain variable amounts of colloidally dissolved pectic substances. Separation of fruit juice polysaccharides by anion‐exchange‐chromatography yielded mainly arabinogalactans (type II) and rhamnogalacturonans. The addition of small amounts of the residual pectins to colloid free juices resulted in a up to 60 % reduction of the flux rates in micro‐ and ultrafiltration systems.
Biological functions of synthetic polysaccharides
Authors: Kobayashi Kazukiyo 
Published: March 2011

AbstractStructurally well‐defined polysaccharide derivatives have been synthesized via ring‐opening polymerization of bicyclic anhydro sugar derivatives and via enzyme‐catalyzed polymerization using phosphorylase. This article describes the following four synthetic polysaccharides, (a) Octadecylated amphiphilic polysaccharides, (b) Regiospecifically fluorinated polysaccharide, (c) Comb‐shaped branched polysaccharide, (d) Graft copolymers having pendant polysaccharide chains. None of these polysaccharides could be prepared by direct chemical modifications of natural polysaccharides. The synthetic polysaccharides are useful as tools to elucidate structure‐function relationships and exhibit various novel biofunctional properties.