bluuebunny/crossref_metadata_2025_split huggingface dataset:
Morphology and kinetics of crystallization of polyethylene from chain disentangled melt
Authors: Galeski A , Psarski M. 
Published: March 2011

AbstractShort description of crystallization processes in linear polyethylene with applied reptation concept and emphasized role of chain entanglements is presented. The influence of chain entanglements in Regimes of crystallization is discussed. The estimation of time of self‐diffusion and time required for complete pull‐out of a macromolecular chain from melt by crystallization forces on the basis of reptation friction leads to the conclusion that a crystallizing macromolecule is reeled out of the melt very quickly (order of microseconds) while other macromolecules are relatively motionless.Fast crystallization of polyethylene does not change end‐to‐end distance of macromolecules while slow isothermal crystallization causes partial disentaglement of chains as it could be concluded from an increased end‐to‐end distance.The route to complete disentanglement is a slow crystallization at elevated temperature (∼230°C) and under high pressure (∼6 kbars). High pressure crystallization delivers polyethylene samples with a high melting point (∼145°C) and completely extended chains (end‐to‐end distance − 1.0). Macromolecular chains in such samples after melting exhibit for a period of several minutes complete or partial disentanglement and can be used for studies of chain entanglements dynamics and also for studies of crystallization from chain disentangled melt.The studies of crystallization of linear polyethylene in disentangled melt showed almost 4 fold increase in the growth rate of spherulite at 126°C (end of Regime II of crystallization) and only 1.1 fold increase at 123°C (beginning of Regime II of crystallization). The results concerning the kinetics of crystallization and nucleation in chain disentagled PE melt as well as resulting morphology are discussed further in terms of Regimes and reptation concepts.
Charge carrier photogeneration and transport in poly(methyl‐phenylsilylene)
Authors: Nešpůrek S. 
Published: March 2011

AbstractOptical excitations in poly(methyl‐phenylsilylene) can be realized within the framework of a chemical bond in the polymer backbone or a side group skeleton. A charge transfer of the electron from the main chain to a side group is necessary to form stable ion‐pairs. Dissociation of the ion‐pairs can be described in terms of the Onsager theory of geminate recombination. The photogeneration efficiency can be improved by an electron acceptor doping. The charge carrier transport is influenced by two factors: delocalized movement inside the conjugated domains and intra‐ and interchain hopping. The electrostatic interactions of polar additives with polarons influence the polaron binding energy and the charge hopping.
Macromolecule‐metal complex interactions as precursors for the catalytic chemical modification of polymers
Authors: Rempel Garry L. 
Published: March 2011

AbstractChemical modification of polymers via catalysis has recently emerged as an area of increasing importance in macromolecular chemistry. It provides an efficient synthetic route for the production of novel polymers with desirable physical properties and functional groups which are often inaccessible by conventional polymerization techniques. Diene‐based polymers and copolymers are ideal for chemical modification because of the technological importance associated with the parent materials and the reactivities of the double bonds in the polymer chain. In employing organometallic catalysts for such modifications, it has been found that the ligand environment of the catalyst as well as the functionality of the polymer has a profound effect on the nature of the macromolecule‐metal complex interaction and the resulting polymer modification. The importance of the macromolecule metal complex interactions and the design of appropriate catalyst systems is illustrated for the hydrogenation, hydroformylation/hydroxymethylation and hydrosilylation of a number of polymers.
Liposome delivered and polymeric metal complexes as potential sensitizers for the photodynamic therapy of cancer
Authors: Wöhrle Dieter , Shopova Maria , Moser Jörg G. , Kliesch Holger , Michelsen Ulrike , Müller Silke , Weitemeyer Andrea 
Published: March 2011

AbstractDifferent possibilities of macromolecular metal complexes as photosensitizers (PS) for their potential use in the photodynamic therapy of cancer are described. The prepared metal porphyrazin derivatives (metals: Zn(II), Si(IV)(X)2) exhibit long wavelength absorption and high singlet oxygen quantum yields under irradiation. One possibility is the incorporation of the PSs in liposomal vesicles giving hydrophobic conjugates with low densitiy proteins in the serum after injection. Good tumor accumulation and photodynamic activities are observed. Increased tumor uptake is also known for Pcs covalently connected via the ligand to poly(ethylene glycol monomethyl ether). New compounds contain the hydrophilic polymer at axial substituents of Si(X)2Pc and Si(X)2Nc. Some newly synthesized compounds with only one functional group exhibit the possibility of coupling to macromolecules like e.g. monoclonal antibodies.
The first bisgermylene, its synthesis and addition to organic halides and dihalides
Authors: Cao Shaokui , Kobayashi Shiro 
Published: March 2011

AbstractThe first bisgermylene with an acyclic structure was synthesized for the first time by one‐pot, two‐step ligand substitution reactions from the 1,4‐dioxane complex of germanium dichloride. The reactions of the bisgermylene with organic halides gave corresponding oxidative addition products, and with organic dihalides gave oligomeric polyadditon products.
Molecular orientation of paramagnetic metal complex by melt‐drawing thermotropic liquid crystalline polymers
Authors: Hanabusa Kenji , Koyama Toshiki , Shirai Hirofusa 
Published: March 2011

AbstractNew liquid‐crystalline polyesters and paramagnetic vanadyl complex were prepared as host polymer and guest complex. Melt‐drawn fibers were made from the blend of host polymer and guest complex at the mesophase temperature. ESR spectra of the melt‐drawn fibers indicated that the base of pyramidal vanadyl complex is completely oriented parallel to the fiber axis.
Building up a conjugated system by the palladium‐catalyzed arylation of ethylene (heck reaction)
Authors: Kiji Jitsuo 
Published: March 2011

AbstractThe palladium‐catalyzed arylation of ethylene under aqueous conditions has been studied. Both NaHCO3‐soluble and ‐insoluble bromo‐and iodoarenes possessing electron‐withdrawing groups react with ethylene to afford styrenes in good yields by water‐soluble PdCl2[tppms]2 (tppms, m‐(diphenylphosphino)benzenesulfonate). The Cr(CO)3 complex of chlorobenzene reacts similarly under organic conditions. These reactions provide a synthetic route to poly(phenylenevinylenes).
Studies on the ultra‐fine transition metal particles dispersed in polymer matrix
Authors: Chen Lei , Yang Wenjun , Yang Changzheng 
Published: March 2011

AbstractA series of complexes of styrene‐4‐vinylpyridine copolymers (SVP) or poly(4‐vinylpyridine) (PVP) and transition metal chlorides were prepared. The transition metal‐polymer complexes were used to prepare the ultra‐fine metallic particles dispersed in polymer matrix by chemical reduction. The effects of the ion concentration and the polymer backbone on the size of these metal particles were studied. It was found that the transition metal ions may coordinate to pyridine groups in precursor polymers after blending. Upon reduction, the metal ions were transformed into the corresponding metal particles in the range of nanometer scale. The protective polymers take an important role to prevent metal particles from oxidation and excessive aggregation.
Liquid crystalline polymers at interfaces
Authors: Halperin Avi , Williams David R.M. 
Published: March 2011

AbstractMain chain liquid crystalline polymers (LCPs) at solid‐nematic interfaces exhibit a variety of phase transition between distorted and undistorted states. In one case the transition results from the confinement of grafted chains immersed in a nematic solvent and subject to homeotropic anchoring. The general features of the transition are similar for long and for short chains. The detailed physics is different since long chains exhibit Gaussian, entropic elasticity while the elasticity of the short chain is due to their rigidity. As a result it is possible to weakly confine long chains without triggering a distortion while for short chains the nematic distortion occurs simultaneously with the buckling of the rod like LCPs. Related effects are found for uniformly adsorbed LCPs and for free, confined chains. Different scenarios are expected when homogeneous anchoring is imposed.
Synthesis and investigation of new water soluble sulfonated rigid‐rod polynaphthoyleneimide
Authors: Timofeeva Galina I. , Ponomarev Igor I. , Khokhlov Alexei R. , Mercier R. , Sillion B. 
Published: March 2011

AbstractA new water‐soluble rigid‐rod sulfonated polynaphthoyleneimide (PNIS) was synthesized. The structure of PNIS has been confirmed by elemental analysis, NMR (1H, 13C), full X‐ray investigation of model compound. Viscosity measurements, sedimentation and light‐scattering experiments of PNIS solutions confirm the suggested aggregation of this polymer and an increase of its molecular weight without being substantially changed in different types of aqueous solution. These aggregates could consist of very tightly packed rigid rods.
Shape persistent macromolecules as building units of complex supramolecular architectures
Authors: Wegner Gerhard 
Published: March 2011

AbstractChain‐rigidity is defined as a structural principle leading to self organization depending on the aspect ratio of the molecular objects and their mutual interactions. These molecular objects serve as the building blocks of systems for which ultrathin layers composed of hairy rod macromolecules (HRM) are an example. Depending on architectural details layered architectures of HRM are models for molecular nanocomposites, exhibit interesting optical, electrochemical, dielectric or barrier properties. They are also designed to be used in devices the performance of which depends on molecular interactions. A systems approach is emphasized as part of the synthetic strategy.
Effect of initiators, lewis acids, deactivators, additives and medium on controlled/“living” carbocationic systems
Authors: Matyjaszewski Krzysztof 
Published: March 2011

AbstractEffect of nucleofugacity of leaving group, X, nucleophilicity/basicity of the formed counteranion, X− or MtXn+1−, and groups stabilizing positive charge in the carbocation, R+, generated from initiator, RX, as well as metal and ligands in the Lewis acids, MtXn, strength of protonic acids, HA, added salts, NR4+X−, nucleophiles, Nu, some other additives and also reaction conditions on controlled/“living” carbocationic polymerization is discussed. The role of all of the components is explained and their rational design for various monomers which can be polymerized cationically to well defined polymers and copolymers is provided.
Anionic synthesis of well‐defined polymer blends by controlled chain‐transfer reactions
Authors: Quirk Roderic P. , Li Jinsong 
Published: March 2011

AbstractThe scope and limitations of controlled chain transfer reactions in living anionic polymerization have been investigated. In contrast to the random nature of normal chain transfer reactions, this procedure first effects controlled living anionic polymerization followed by addition of a stoichiometric amount of suitable chain transfer agent when the monomer has been completely consumed. The resulting anionic species is then used to initiated polymerization of a second monomer charge with the same monomer or with a different monomer. A variety of hydrocarbon acids and amine compounds with pKa values in the range of 30–40 have been evaluated as chain transfer agents in the presence and absence of coordinating ligands. Efficient chain transfer to poly(styryl)lithium has been observed using 1,1‐diphenylpropane. Reinitiation efficiency to both styrene and butadiene monomer was quantitative and controlled blends of different molecular weight polystyrenes or blends of polystyrene with polybutadiene have been prepared. The use of these chain transfer reactions to prepare functionalized polymers has also been investigated.
Polyisobutylene based designed polymers
Authors: Mishra Munmaya K. 
Published: March 2011

AbstractThe field of cationic polymerization has moved center stage with the recent discovery of living polymerization that lead to the design of polymers with controlled molecular architecture. This report will provide a brief introduction of living cationic polymerization of isobutylene (IB) by tertiary ethers, and new cationic initiating systems based on peroxides and hydroperoxides. This paper will also briefly review some our recent work on the design of block copolymers via multi‐mode polymerization (cationic–radical transformation) including the synthesis of star‐blocks. The application of polyisobutylenes (PIBs) in the design of “beaded molecular strings,” a new class of molecular assembly will be discussed as well.
Investigation of the Mechanism of Crossover Reaction of p‐Dicumyl chloride/BCl3/Isobutylene System by Glass Fiber Optic Photometry
Authors: Kéki S. , Bogács L. , Cs Bogács , Zsuga M. 
Published: March 2011

AbstractA thorough kinetic investigation was done by measuring the optical density of reaction mixtures of the pDCC/BCl3 initiating system in the presence and in the absence of monomer and added salt at 500 nm and at −80°C. The absolute rate constants of elementary steps of the ion generation and cationation were evaluated by computer using a fitting method for determination of the parameters occurring in the kinetic model. The key activated species of the mechanism are identified to be colorless donor‐acceptor complexes. The color of reaction mixtures is caused by ionized species. On the basis of the calculations and other evidences, a well‐established mechanism is proposed. Both ‐tC‐Cl and ‐tC‐OH endgroups were found by MS/EI. GPC analysis of the reaction products indicates that the major product is dimer under the reaction conditions applied.
Tetraalkylammonium salts as additives in anionic polymerization of methyl methacrylate
Authors: Tsvetanov Christo B. , Novakov Christo P. 
Published: March 2011

AbstractThe anionic polymerization of methyl methacrylate was carried out in the presence of t‐BuOK/Quaternary ammonium salt (QAS) and α‐lithio‐ethylisobutyrate/QAS in toluene and THF. Seven QAS and one quaternary phosphonium salt of different size and shape were used as modifiers. With the aid of the model system alkali picrate/QAS, it was found that the interaction between the picrate salt and QAS in toluene does not proceed as a pure cation exchange reaction. Two types of adducts were distinguished: Initiator/QAS with a very long hydrocarbon chain (>C12) promote isotactic placement, while the adducts t‐BuOK/QAS with two or more bulky substituents produce a highly syndiotactic polymer with high conversion and comparatively low polydispersity in pure toluene.
Application of magnetic resonance spectroscopies to the characterisation of elastomer/filler systems
Authors: Legrand André Pierre 
Published: March 2011

AbstractContribution of the magnetic resonance spectroscopies to the determination not only of the chemical structure but also of the dynamics of the polymer chains is examined. Analysis of such complex systems involves different aspects. Questions as: the nature of the crosslinking via sulfur bridges, presence of additives, influence of the heat treatments, behaviour under strain, analysis of the interphase … are considered. A part is devoted to the dynamic behaviour of the chains in the interphase elastomer/filler.
Surface microstructure of carbon black: Advances in characterization by scanning tunneling microscopy
Authors: Donnet Jean‐Baptiste , Wang Tong Kuan 
Published: March 2011

AbstractThe recent advances in the characterization of the surface structure of carbon black by scanning tunneling microscopy (STM) are reported. The atomic organization, at the surfaces of several carbon blacks, is well resolved by STM and a local paracrystalline structure model is proposed, where the distorted carbon layer and thus the unequal inter‐layer distance are evidenced on the basis of the classical turbostratic stacking. The quantitative analysis of the STM image, which enables a quantitative assessment of the surface crystallinity and of the nanoscale roughness, is presented.
Rheological properties of filled polymers
Authors: Carreau Pierre J. , Lavoie Paul‐André , Bagassi M'Hammed 
Published: March 2011

AbstractThe rheological properties of two model suspensions using a Newtonian polymeric matrix are presented and discussed in light of results presented in the literature. It is shown that particle‐particle interactions in concentrated suspensions are responsible for a gel‐type behavior at very small strain and strain hardening at a critical strain. Suspensions of concentrated colloidal particles in a Newtonian matrix behave like typical viscoelastic molten polymers, but the properties are strongly dependent on the solids dispersion, and strain at small strain. A simple rheological model is proposed to describe the shear viscosity of these suspensions.
Physical properties of sol‐gel derived poly(Vinylidene Fluoride)/Silica hybrid
Authors: Yano Shoichiro , Okubo Nobuaki , Takahashi Kazutaka 
Published: March 2011

AbstractPoly(vinylidene fluoride) (PVDF) was incorporated in situ with silica by a sol‐gel process involving tetraethoxysilane. The mechanical properties of these in situ hybrids were compared with those of PVDF composites mechanically blended with 14‐nm diameter fumed silica particles. The ultimate strength of the in situ hybrids was higher than that of the blend composites, since fumed silica particles aggregate and act as mechanically weak points. The thermal analysis, dynamic viscoelastic properties, and dielectric properties were compared. The β‐relaxation of PVDF caused by the glass transition was observed at around −40°C in the differential scanning calorimetry (DSC) and the mechanical tan δ curves and at −30°C in the dielectric loss factor (ϵ”) curve. The αc‐relaxation due to the molecular motion in the crystalline phase occurred at 61°C in DSC curve, at 100°C in the tan δ curve, and at 80°C in the ϵ” curve. The peak positions of these relaxations did not change, but the peak intensities were decreased with the increase in silica content for both the in situ hybrids and blend composites. The activation energies for PVDF were calculated as 136 kJ/mol for the β‐relaxation and 96 kJ/mol for the αc‐relaxation. The result that these activation energies did not depend on silica content may indicate the weak interaction between PVDF and silica.
Subcutaneous hydrogel reservoir system for controlled drug delivery
Authors: Kuzma Petr , Moo‐Young Alfred J. , Mora Daniel , Quandt Harryp , Bardin Clyde W. , Schlegel Peter H. 
Published: March 2011

AbstractHydro Med Sciences has developed a subcutaneous reservoir hydrogel implant capable of long term delivery of predetermined doses of various active compounds. The implant is a small‐diameter, thin‐walled cylindrical capsule containing a therapeutic agent. The hydrogels used for this application were Hydron* type copolymers of 2‐hydroxyethyl methacrylate (HEMA). These non‐erodible hydrogels are known to be biocompatible, swell reversibly in an aqueous environment, resist biodegradation and do not support microbial growth.
A hydrogel with rubber elasticity transition
Authors: Nagasaki Yukio , Kazama Kenji , Honzawa Eiichi , Kato Masao , Kataoka Kazunori , Tsuruta Teiji 
Published: March 2011

AbstractReaction between dimethyldivinylsilane and 3,6‐diazaoctane in the presence of 3‐lithio‐3,6‐diazaoctane yields a new telechelic oligomer, poly(silamine), which consists of alternating 3,3‐dimethyl‐3‐silapentane and N,N′‐diethylethylenediamine units in the main chain. Poly(silamine) shows unique phase transition properties in response to the degree of protonation of amino groups in the polymer. Poly(silamine) also shows a strong interaction with several anions. Due to the interaction between poly(silamine) and anions along with the protonation of amino groups in the poly(silamine), the rubber elasticity of poly(silamine) is drastically changed. A discrete volume change can be observed when the environmental pH of the poly(silamine) gels is varied. This can be explained not only by a change in ionic osmotic pressure but also by a change in the rubber elasticity of the networks in the gel.
Noninvasive optical characterization of hydrogels
Authors: Weiss Aryeh M. , Khayutin Leonid , Bentolila Alfonso , Domb Abraham 
Published: March 2011

AbstractThis paper presents results based on concentration quenching of fluorescence polarization (cqfp), which demonstrate the feasibility of using cqfp to measure changes in hydrogel‐membrane hydration. This is accomplished by binding fluorescent molecules to the hydrogel matrix, and showing that the fluorescence polarization is a monotonic function of fluorophore concentration. Films based on crosslinked 2‐hydroxyethyl methacrylate containing lissamine side groups (10−4‐10−7 mol/l) were mounted in a special cell which provided an aqueous environment, and in which polarized fluorescence could be measured. An argon‐ion laser provided polarized excitation at 488nm, and the polarized fluorescent emission was detected. The correlation between the fluorescence polarization and the bound dye concentration was found to correspond to the theoretically expected behavior.
Mechanical and wear properties of poly(vinyl alcohol) hydrogels
Authors: Cha Won‐Ill , Hyon Suong‐Hyu , Oka Masanori , Ikada Yoshito 
Published: March 2011

AbstractPoly(vinyl alcohol)(PVA) hydrogels with low water contents were prepared by low temperature crystallization of PVA solution from a dimethyl sulfoxide/H2O mixed solvent, followed by high‐temperature annealing after drying and the subsequent re‐swelling with water. The tensile strength and dynamic modulus of PVA hydrogels increased upon annealing, irrespective of the degree of polymerization (DP) of PVA, but always at the sacrifice of the water content of hydrogel. In addition to the mechanical strength, the hardness of PVA hydrogels was improved by lowering the water content. The highest tensile strength(20 MPa) and the highest dynamic modulus(180 MPa) were obtained when hydrogel was prepared from PVA with DP of 11 000 and annealed at 140°C for 24 h. The wear resistance strongly depended on the mechanical strength and coefficient of friction of PVA hydrogels. The wear volume of the hydrogel prepared from PVA with DP of 8 800 decreased with the decreasing coefficient of friction and the increasing mechanical strength of PVA hydrogel except for the 25 wt% PVA hydrogel at 2.5 MPa. Furthermore, any wear particles were not detected for the 45 wt% PVA hydrogel at 2.5 MPa and the 25 wt% PVA hydrogel at 2.0 and 2.5 MPa.
Synthesis and characterization of highly wettable hydrogel coatings for immobilization of marine bacteria
Authors: Gatenholm P. , Michálek J. , Vacík J. 
Published: March 2011

AbstractThis study evaluates hydrogels based on 2‐hydroxyethyl methacrylate (HEMA) and diethylene glycol ester of methacrylic acid (DEGMA) as candidates for a suitable matrix for immobilizing marine bacteria. Results are presented of investigations of the effect of monomer structure and polymer composition on wettability and mechanical properties. We also studied the effect of composition on heat produced during polymerization, an important factor affecting bacterial viability during the process of immobilization. Hydrogels based on DEGMA in artificial sea water solution demonstrate the attractive combination of good mechanical properties and high water content. At low concentrations of monomer, little heat is produced during polymerization. These properties make DEGMA‐based hydrogels suitable for immobilizing marine bacteria.