bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rheological and DSC studies of mixtures of gellan gum and konjac glucomannan
Authors: Miyoshi Emako , Takaya Tomohisa , Nishinari Katsuyoshi , Williams Peter A. 
Published: March 2011

AbstractThe interaction between gellan gum (GELL) and konjac glucomannan (KGM) with and without sodium chloride, potassium chloride, calcium chloride and magnesium chloride has been monitored using mechanical spectroscopy and differential scanning calorimetry (DSC). The rheological results indicated that the synergism occurred at sufficient low temperatures where individual helices of GELL molecules were sufficiently aggregated. With progressive addition of monovalent cations, storage shear modulus G' and loss shear modulus G” for mixtures gradually increased, and not only the helix‐coil transition temperature of GELL molecules in mixtures but also the sol‐gel transition temperature for mixtures shifted to higher temperatures with increasing concentration of salts. Moreover, in the presence of sufficient monovalent cations, mixtures formed an elastic gel with large thermal hysteresis. In the presence of divalent cations, the synergistic interaction was promoted up to a certain concentration, however, with more progressive addition of divalent cations, the main structure formed by aggregates of GELL helices would be smaller, so that mixtures could not form a gel in the presence of excessive divalent cations. DSC results indicated that the intermolecular binding complexes between GELL and KGM molecules would not occur, but KGM markedly influenced the disorder‐order transition of GELL molecules. We have suggested that KGM was attached to the surface of large aggregates of GELL helices, and since cations promote GELL self‐aggregation by a screening effect, the synergistic interaction between GELL and KGM was promoted with increasing concentration of salts. However, excessive divalent cations formed various aggregates of GELL helices with different thermal stabilities, so that the phase‐separation in GELL/KGM mixtures was promoted in the presence of excessive divalent cations.
Association behavior of living anionic lipophobic head‐groups in hydrocarbon mileau
Authors: Fetters L. J. , Huang J. S. , Stellbrink J. , Willner L. , Richter D. 
Published: March 2011

AbstractThe commercial applications of anionic polymerization have become wide‐spread with regard to the preparation of linear and star shaped homopolymers and block copolymers (Diene‐35TM, KratonTM, VectorTM, SolpreneTM, K ResinTM and ShellVisTM). Furthermore, randomized styrene/butadiene linear copolymers (SolpreneTM) and low molecular weight, 10K or less, polybutadienes (LithenesTM) of various microstructures are commercially available. Recently Liquid KratonsTM with OH functional units in place on one or both chain ends have become items of commerce. The lithium based systems yield materials of uniform composition and molecular weights with virtually monodisperse molecular weight distributions. Both molecular weight and composition are tunable via the simple expedient of manipulating the monomer/initiator ratio. Although the synthetic aspects of these anionic systems have been well‐mastered and exploited over the years the mechanistic features have remained controversial; issues which revolve around active center aggregation behavior and the reactivity (or its absence) of these self‐assembled anionic lipophobic head‐groups. Thus a study of these systems was undertaken using modern scattering techniques and data analysis procedures.Small angle neutron scattering (SANS) in combination with dynamic and static light scattering, DLS and SLS, has been used to evaluate the association behavior of the styryl‐ and dienyllithium head‐groups in benzene and cyclohexane solutions. Both types of lipophobic active centers were found to aggregate as dimers which in turn can self‐assemble to yield large‐scale wormlike micelles (prolate ellipsoids). These systems thus emulate the behavior of diblock copolymers and surfactants in their capacity to form flexible cylindrical micelles. It was also found for all head‐groups that the combination of long chain lengths and high polymer concentrations favored the presence of the dimer structure. This commonality of aggregation state is in consonance with results given in 1964.
The short time regime of segmental dynamics of glass‐forming polymers
Authors: Colmenero Juan , Arbe Arantxa 
Published: March 2011

AbstractThe short time regime (10−13 s ≤ t ≤ 10−11 s) of the segmental dynamics of several glass‐forming polymers with different chemical microstructure and glass‐transition temperature has been investigated by means of time of flight (TOF) neutron scattering techniques. In this paper we present a summary of the main results obtained as well as the theoretical framework proposed by us to interpret these results. The main conclusion is that the segmental dynamics of glass‐forming polymers display in the very short time range (t = 2 ps) a crossover from a simple exponential behaviour towards a non‐exponential regime. The first exponential decay, which is controlled by C‐C rotational barriers, can be understood as a trace of the behaviour of the system in absence of the effects (correlations, cooperativity, memory effects…) which characterise the dense supercooled liquid like state against the normal liquid state. The non‐exponential regime at t > 2 ps corresponds to what is usually understood as α and β relaxations. Some implications of these results are also discussed.
Nonlinear dynamics of melted polymer layers
Authors: Semenov A. N. , Subbotin A. V. , Hadziioannou G. , Ten Brinke G. , Manias E. , Doi M. 
Published: March 2011

AbstractA theory for non‐linear rheology of molten polymer layers between solid surfaces in the Rouse regime is discussed. It is shown that the effect of finite extensibility of polymer chains leads to the characteristic 1/3 power law for the shear stress vs. shear velocity in the regime of high velocities. It is also shown that bridging polymer fragments connecting the two surfaces play an important role for the rheology if the effective monomer friction in the immediate vicinity of the surfaces is much higher than far from the surfaces. In particular we predict that shear stress is decreasing with shear velocity u in a limited range between u1 and u, min. This effect results in a possibility of stick‐slip periodical dynamics of the layer under a constant imposed velocity.
Brownian configuration fields: A new method for simulating viscoelastic fluid flow
Authors: Brule Ben Van Den , van Heel Ton , Hulsen Martien 
Published: March 2011

AbstractIn this paper a new method for calculating viscoelastic fluid flows is presented. The polymer stress is not calculated from a closed form constitutive equation but from a microscopic model. Instead of considering the motion of individual molecules we calculate the evolution of an ensemble of configuration fields, representing the internal degrees of freedom of a model molecule. The configuration fields are deformed and convected by the flow and are exposed to thermal motion. The field description is incorporated in a finite element calculation of the flow field where the stress in the fluid is now obtained from an average taken over all the configuration fields. The results for flow past a cylinder for a Hookean dumbbell suspension will be compared with the results obtained from a fully macroscopic calculation of the equivalent Oldroyd‐B model. Excellent agreement is obtained.
New organo‐soluble polyimides for optical, microelectronic and fiber applications
Authors: Harris Frank W. , Li Fuming , Lin Sheng‐Hsien , Chen Jyh‐Chien , Cheng Stephen Z. D. 
Published: March 2011

AbstractA novel class of organo‐soluble polyimides has been developed based on monomers containing twisted‐biphenyl structures. Thus, 2, 2'‐disubstituted‐4, 4'‐diaminobiphenyls and 2, 2'‐disubstituted‐4, 4', 5, 5'‐biphenyltetracarboxylic dianhydrides have been prepared and polymerized in refluxing phenolic solvents. The polyimides, some of which are soluble in ketone and ether solvents, can be readily solution cast into colorless thin films. The rigid polymer chains align parallel to the substrate surface (in‐plane orientation) during the casting process, which results in anisotropy in the film properties. The anisotropy in the refractive index has been used in the development of compensation layers for liquid crystal displays. The polymers have also been dry jet‐wet spun from phenolic solutions to afford fibers that display tensile strengths of 3.5 GPa and moduli of 130 GPa.
Quantum semiempirical study of the reactivity of monomers in the synthesis of aromatic polyamides and polyimides
Authors: Lozano Angel E. , De Abajo Javier , De La Campa José G. 
Published: March 2011

AbstractThe amidation and imidation reactions have been studied by quantum semiempirical methods, determining the influence of different types of substituents on the geometries and electronic parameters of diamines, either unsilylated or silylated, diacyl chlorides and dianhydrides. It was confirmed that the energy of the frontier orbitals, ELUMO in the electrophiles and EHOMO in the nucleophiles, is the main parameter that controls the reactivity of the different monomers.
New phytoactive polymers prepared by polycondensation
Authors: Manolova Nevena , Ignatova Milena , Rashkov Iliya , Sepulchre Maurice , Spassky Nicolas 
Published: March 2011

AbstractSome new poly(ether‐ester)s (PEEs) and poly(ether‐amide)s (PEAs) with polyether sequences linked by tartrate units have been synthesized. Derivatives bearing residues from the synthetic plant‐growth regulator 1‐naphthylacetic acid (NAA) as pendent groups and end‐groups have been prepared by esterification of PEEs and PEAs with NAA. Polymers bearing residues from pyridine‐2, 6‐dicarboxylic acid (a herbicide) in the main chain have been prepared. The hydrolysis has been found to depend on the structure of the polymer carrier, on pH of the medium and on the ability of the polymers to form complexes with polyacids. The phytosanitary activity of the new polymers has been related to the particular features of their hydrolysis behaviour.
Atomic force microscopy and enzymatic degradation of oyster shell protein and poly(aspartate)
Authors: Steven Sikes C. , Martin Frances , Wierzbicki Andrzej , Wheeler A. P. 
Published: March 2011

AbstractOyster shell protein (OSP), an aspartate‐enriched regulator of crystallization, was readily observed in its natural condition by atomic force microscopy (AFM) of fragments of oyster shell. The fragments of shell consisted of layers of calcite mineral, termed folia, to which arrays of protein molecules are attached. Modification and removal of the OSP following treatment with several proteolytic enzymes such as subtilisin, carboxypeptidase B, and endoproteinase Glu‐C were also observed by AFM. Similarly, poly (aspartate), a polypeptide analog of the OSP, was visualized by AFM on both calcite and mica. Images of poly(aspartate) before and after treatment with lipase demonstrated the potential utility of AFM in degradation studies. The mechanism of hydrolysis is not clear in that lipase normally is considered to be an esterase and not a peptidase.
The concept of cohesional entanglement
Authors: Qian Renyuan 
Published: March 2011

AbstractA concept of cohesional entanglement through local nematic interaction of neighboring chain segments has been introduced in addition to the usual topological entanglement of chains. As topological entanglement is important to properties of the polymer in the rubbery and flowing states at temperatures well above its Tg, the cohesional entanglement is important to properties at temperatures around and below Tg. Evidences for the existence of cohesional entanglements are presented. From the point of view of cohesional entanglement the DSC curves of glass transition and the effect of sub‐Tg annealing are discussed. Finally the stress peak on yielding during uni‐axial drawing, rejuvenation of sub‐Tg annealed polymer by drawing and anti‐plasticization of plastics are discussed based on the concept of cohesional entanglement.
Electroluminescence in polymers
Authors: Yang Zhou , Hu Bin , Karasz Frank 
Published: March 2011

AbstractPolymeric materials containing chromophores are promising for electroluminescent (EL) device applications including displays and lighting. We report EL for a series of copolymers containing uniform conjugated chromophores and nonconjugated spacers. The emission color of the copolymers can be varied by adjusting the molecular structure to alter the energy gap between the HOMO and LUMO of the chromophore. The design can also be used to tailor other properties of the polymer, such as the glass transition temperature, by varying the length of the nonconjugated spacers.
Metal induced photoluminescence quenching of a phenylene vinylene oligomer and its recovery
Authors: Choong Vi‐En , Park Yongsup , Gao Yongli , Hsieh Bing R. , Tang Ching W. 
Published: March 2011

AbstractMetal/polymer interfaces play an important role in polymeric light emitting diodes (LEDs). In typical organic light‐emitting devices, metallic electrodes are used to inject charged carriers into the organic electroluminescent (EL) medium. However, what other effects the metals have on the organic medium is not well known. In this work, we report severe photoluminescence (PL) quenching of organic thin films comprising of one of the most useful materials, namely 1,4‐bis[4‐(3,5‐di‐tert‐butylstyryl)styryl]benzene (4PV), upon sub‐monolayer deposition of Al, Ag, and Ca in an ultra high vacuum environment. The severity of the luminescence quenching may greatly affect the EL device performance. Gap states at the Ca/4PV interface are shown to be responsible for the PL quenching. The oxidation of Ca resulted in the removal of the gap states and the recovery of the quenched PL.
The interaction of cationic polymers with human hair
Authors: Pfau Andreas , Hössel Peter , Vogt Sabine , Sander Ralf , Schrepp Wolfgang 
Published: March 2011

AbstractWe present a combination of electrochemical methods, i.e. polyelectrolyte titration and streaming potential measurement, and AFM to characterise the adsorption and desorption behaviour and the morphology of a set of polyquaternium polymers on human hair. Specific charge density and molar mass are correlated to the amount of adsorbed polymer and the ease of desorption. Results are in line with a simple model of coulombic interaction between hair and polymer and are interpreted on this basis.
Crystallization and melting behaviour of poly(ferrocenylsilanes)
Authors: Hempenius Mark A. , Lammertink Rob G. H. , Julius Vancso G. 
Published: March 2011

AbstractA series of poly(ferrocenyldimethylsilanes) was prepared anionically in order to study their melting behaviour. The DSC traces of these polymers displayed multiple endotherms that could be assigned to melting of lamellae with varying thicknesses. Upon heating, thinner lamellae are converted into thicker ones in a continuous melting‐recrystallization process.
Novel styrene‐butadiene block copolymers by sequential and statistical copolymerization of corresponding macromonomers
Authors: Grande Daniel , Six Jean‐Luc , Héroguez Valérie , Gnanou Yves , Fontanille Michel 
Published: March 2011

AbstractThis paper concerns the synthesis of two different structures of styrene‐butadiene block copolymers that were respectively obtained via sequential and statistical ring‐opening metathesis copolymerization of norbornene‐terminated polystyrene (PS) and polybutadiene (PB) macromonomers. The stimulus for preparing such styrene‐butadiene copolymers originates from the observation that phase‐separated morphologies in block copolymers not only depend on the respective size of the blocks and the interaction parameter (χ), but also on the topological constraints introduced in the copolymer structure. From the differential scanning calorimetry study that was carried, it can be inferred that the two types of copolymers ‐prepared by sequential and statistical copolymerization of PS and PB macromonomers respectively‐ exhibit quite different phase separation behaviors, indicating that they develop distinct equilibrium domain morphologies.
Synthesis of novel block copolymers through electron transfer system by smi2
Authors: Nomura Ryoji , Endo Takeshi 
Published: March 2011

AbstractThis paper summarizes our recent efforts to offer block copolymers through the transformation reactions of a cationic growing center into an anionic one by the utilization of divalent samarium complexes. Four types of transformation reactions are described, and their scope and limitations are discussed. Several applications of these transformation reactions are also presented.
Intelligent networks based on poly(oxyethylene)
Authors: Tsvetanov Christo B. , Stamenova Rayna , Dotcheva Dobrinka , Doytcheva Maria , Belcheva Nadya , Smid Johannes 
Published: March 2011

AbstractFilms of PEO and PEO blends were efficiently crosslinked by exposure to ultraviolet radiation with high‐pressure mercury lamp. Photochemical crosslinking proceeded in the presence of photoinitiator such as benzophenone or pentaerythritol triacrylate. PEO networks obtained by UV irradiation in the presence of potassium salts (thiocyanate, perchlorate and triflate) as templates showed enhanced cation binding ability for Li+ and Na+ cations. Cationic networks were prepared from crosslinked PEO modified with ethyl methacrylate dimethyl dodecyl ammonium bromide. Stimuli‐sensitive hydrogels (pH and temperature) were prepared from combinations of PEO and poly‐N‐isopropyl acryl amide, polyvinyl methyl ether, polyvinyl acetate and poly‐2‐vinyl pyridine subjected to UV irradiation.
Novel polyolefin materials via catalysis and reactive processing
Authors: Suhm Jürgen , Heinemann Johannes , Wörner Christof , Müller Philipp , Stricker Florian , Kressler Jörg , Okuda Jun , Mülhaupt Rolf 
Published: March 2011

AbstractRecent advances in transition metal catalyzed olefin polymerization and melt processing stimulate the production of new polymers derived from old monomers. Modern polyolefin processes do not require polymer purification and give excellent control of molecular and supermolecular polyolefin architectures. Progress in catalyst design and preparation of tailor‐made homo‐and copolymers is highlighted for isotactic, syndiotactic, atactic and stereo‐block polypropylene (PP), novel 1‐olefin copolymers, and ethylene copolymers with polar monomers, e.g., CO and acrylics. Today polyethylene short‐and long‐chain‐branching is controlled either by uniform ethylene copolymerization with 1‐olefins using single‐site” metallocene catalysts, or by migratory polyinsertion of ethylene, respectively. Stiff cycloaliphatic polymers expand the frontiers of polyolefins into engineering applications. New families of polyethylenes and EPM with pendent polypropylene chains are obtained via copolymerization of PP macromonomers or polymer‐analoguous coupling of functionalized PP during melt processing.
Surface modification of polyolefins by photografting of acrylic monomers
Authors: Decker C. , Zahouily K. 
Published: March 2011

AbstractHigh‐speed surface modification of polypropylene (PP) and polyethylene (PE) films has been achieved by liquid phase photograft polymerisation of acrylic acid (AA) and hydroxypropyl acrylate (HPA). Benzophenone was used as photoinitiator to generate polymer radicals at the surface of the polyolefin film. The grafting reaction was carried out in aqueous solution or with the neat monomer, which was laminated between two PP films, in the presence of air. Under the intense illumination of a UV‐curing line, acrylic acid was grafted within seconds to polypropylene films or fabrics, which were thus made hydrophilic. Direct evidence of surface grafting was obtained through infrared spectroscopy analysis and surface energy measurements. This continuous photografting process proved to be very efficient to improve the adhesion of UV‐cured acrylate coatings on polyolefin‐made materials.
The role of pyridine derivatives in living carbocationic polymerization: Lewis base or nucleophile?
Authors: Bae Young Cheol , Faust Rudolf 
Published: March 2011

AbstractThe living cationic polymerization of isobutylene induced by the 2‐chloro‐2,4,4‐trimethylpentane/TiCl4/hexane:methyl chloride (60:40, v:v)/‐80°C system was studied in the presence of pyridine derivatives. Protic initiation, substantial in the absence of these additives, was virtually eliminated in their presence, and polyisobutylenes with controlled molecular weight and narrow molecular weight distribution were obtained. With some additives, however, proton elimination occurs, resulting in the exclusive formation of the exo olefin. The rate of elimination is independent of monomer concentration, i.e., it occurs during and after the polymerization. Results suggest that the proton elimination is due to the presence of an uncomplexed base, especially when complex formation with TiCl4 is hindered by steric compression, but its approach of the polymer cation is not fully blocked.
Alkyl chloride‐boron trichloride initiated polymerizations of isobutylene: Detailed analysis of the initial propagation steps
Authors: Mayr Herbert , Roth Michael 
Published: March 2011

AbstractLiving oligomerizations of isobutylene initiated either by cumyl chloride, the [1:1]‐adduct of cumyl chloride to isobutylene (P), the [1:2]‐adduct of cumyl chloride to isobutylene (P2), diisobutylene hydrochloride (P1'), or triisobutylene hydrochloride (P2') have been studied in presence of BCl3 and benzyltriethylammonium tetrachloroborate. In contrast to common opinion, the gross propagation rates of the various telechelics depended significantly on the degree of polymerization with krel = 0.07, 1.8, 2.3, 1.3, 1.1, 1.0, 1.0 for Ph‐C(CH3)2‐[CH2‐C(CH3)2]n‐Cl with n = 1, 2, 3, 4, 5, 6, 7, respectively. These results are compared with the initiation efficiencies of (CH3)3C‐(CH2‐C(CH3)2]n‐Cl (Krel = 0.3 and 0.8 for n = 1 and 2, respectively). The consequences for the synthesis of telechelics with very narrow molecular weight distribution are discussed.
Electron transfer at the solid liquid interface; new insights on the mechanism of formation of the grignard reagent
Authors: Chanon Michel , Négrel Jean Claude , Bodineau Nicolas , Mattalia Jean Marc , Péralez Eric , Goursot Annick 
Published: March 2011

AbstractThe strong inhibiting effect of trace quantities of selected compounds on the reaction between ultra fine particles of magnesium and alkyl halides in THF strongly suggests that the generally accepted linear mechanism should be replaced by a chain mechanism. The reactivity of batteries of free radical clocks centered on an aliphatic skeleton displays unexpected leaving group effects. Such effects could be rationalized according to a variety of mechanistic schemes. The main ones are: 1) coexistence of polar and electron transfer routes, 2) participation of solvated electrons in the mechanism, 3) gradient of reactivity starting from the magnesium surface to the bulk solution. A series of experiments aiming at a choice between these possibilities is described.