bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation of monodisperse latexes and study of their rheological properties
Authors: Zecha Helmut 
Published: March 2011

AbstractThe synthesis of (monodisperse) poly(styrene) latexes was reexamined using sodiumdodecyl sulfate as emulsifier and potassium persulfate as initiator. It has been shown, that at fixed emulsifier concentration cE the variation of persulfate amount produces similar particle size variations as changes of electrolyte (potassium sulfate) concentration at a given low initiator level. For cE << cmc a maximum of particle size versus initiator or electrolyte concentrations has been found. Concentrated monodisperse poly(styrene) dispersions and carboxylated latexes up to 50% have been prepared by a carefully controlled seeding process using monomer feed.Particle size influence on steady shear viscosity has been studied for different kinds of polymer dispersions: for electrostatic stabilized poly(styrene) latexes at high ionic strengths, for electrostatic and sterically stabilized carboxylated latexes at different pH values and for steric stabilized dispersions of poly(vinyl chloride) in plasticizer (dioctyl phthalate). All three kinds of dispersions give pronounced particle size effects on viscosity, which is different from hard‐sphere‐behaviour. Simple model equations have been formulated to describe the concentration and shear rate dependence on viscosity. Particle size influence may be discussed on the basis of the effective hydrodynamic particle diameter. Causes for the increase of the hydrodynamic particle size are given either by surface swelling or by the formation of particle clusters which are formed and destroyed within the shear field.
Effect of a bi‐unsaturated monomer on the emulsion polymerization of ethyl acrylate
Authors: Capek Ignac , Kostrubová Jana , Bartoň Jaroslav 
Published: March 2011

AbstractThe emulsion polymerization and copolymerization of ethyl acrylate with a bi‐unsaturated comonomer (divinylbenzene, 1,6‐hexamethylene diacrylate), present in small proportions, in the presence of anionic emulsifier sodium dodecyl sulfate have been kinetically investigated at 60°C under batch conditions by gas chromatograhy and gravimetric methods. The rate of polymerization in interval 2 was found to be proportional to the 0,37, 0,23, and 0,5 power of the emulsifier concentration for the system A (ethyl acrylate), the system B (ethyl acrylatedivinylbenzene), and the system C (ethyl acrylate/1,6‐hexamethylene diacrylate). Divinylbenzene was found to decrease both the rate of polymerization and the polymer particle size. Addition of 1,6‐hexamethylene diacrylate slightly increases both the rate of polymerization and the polymer particle size.
New prospects for “living” anionic polymerization of (meth) acrylic esters
Authors: Teyssié PH. , Fayt R. , Hautekeer J. P. , Jacobs C. , Jérôme R. , Leemans L. , Varshney S. K. 
Published: March 2011

AbstractThe living low temperature polymerization in polar solvents of most methacrylates, even functional ones, can now be performed by direct and experimentally convenient anionic methods, thanks to the use of α‐methylstyrene and of complex‐purified monomers. A diversified family of block copolymers has thus been generated, that are used as compatibilizing agents in the designing of interesting heterophase materials: i.e. blends of polymers and inorganic fillers, and liquid‐solid dispersions.The living polymerization of acrylates (or of methacrylates under more drastic conditions) raises additional requirements: they have been met to a large extent by the use of specific ligands of the growing ion‐pair. Resulting structures such as f.i. block copolymers and end‐functionalized oligomers of a low dispersity, should have a great interest in the molecular engineering of (meth)acrylate‐based products.Finally, these new initiators lend themselves to structural and mechanistic studies which should shed some light on the critical features of these living propagation processes.
Effect of reaction medium on ionic lactam polymerization
Authors: Šebenda J. 
Published: March 2011

AbstractRing‐size and substitution greatly affect the permittivity and donor‐acceptor properties of lactams and their derivatives as well as of the corresponding polymers. Permittivity changes occurring during bulk polymerization affect dissociation equilibria and the very high increase in permittivity during polymerization is responsible for the autoacceleration observed in the anionic polymerization of the seven‐membered lactam. In diluted solution, pronounced effects of the nature of solvent or additive have been observed in anionic polymerization of substituted four‐membered lactams. Whereas the initial rate of polymerization is independent of the monomer concentration, the apparent order in the monomer increases and the rate of polymerization in most solvents decreases during polymerization, except in solvents of very low polarity. Changes of permittivity and conductivity during and after polymerization indicate, that changes in the solvation and rearrangement of the growth center are responsible for its varying activity. These processes increase the reactivity during ageing of the living system. Similarly to other heterocyclic monomers, the cationic polymerization of N‐acyllactams is rather insensitive to the permittivity of the reaction medium.
A chemical approach to the problem of slow initiation in living cationic polymerizations
Authors: Zsuga Miklós , Kelen Tibor , Kennedy Joseph P. 
Published: March 2011

AbstractThe effect of slow initiation on initiation efficiency and MWD has been investigated, with regard to the living carbocationic polymerization of isobutylene. The initiating system trans−2,5‐diacetoxy‐2,5‐dimethyl−3–hexene(DiOAcDiMeH6)BCl3 has been investigated at −35°C in CH3Cl. Based on considerations valid also for anionic polymerizations, the following methods have been applied to increase the initiation efficiency: 1. Increasing [Mo]/[Io] (batch, AMI) or [ΔM].j/[Io] (IMA). The applicability of this method is limited by the solubility of the polymer. 2. Increasing ki/kp, by (i) increasing ki, e.g., by introducing an electron withdrawing substituent into the initiator, (ii) decreasing kp, e.g., by the addition of a strong electron donor (DMSO) to the system, (iii) using Cl‐CH2‐CH2‐Cl.
Block copolymers of polyacetals
Authors: Franta E. , Refai J. , Durand C. , Reibel L. 
Published: March 2011

AbstractThe polymerization of 1,3‐dioxolane was carried out using trifluoromethanesulfonic acid (triflic acid) as catalyst, in the presence of an oligomeric diol, α‐hydro‐ω‐hydroxypoly(oxyethylene) (PEOG) or α‐hydro‐ω‐hydroxypoly(oxytetramethylene) (poly‐THF‐diol). When PEOG was used, a linear increase of the number average molecular weight versus conversion was observed. A triblock copolymer was obtained as well as small cycles in their usual equilibrium concentration. When poly‐THF‐diol was used, fast transacetalization provoked the “polycondensation” of the diol through acetal linkages at the very onset of the reaction, leading to a very inhomogeneous mixture. After equilibrium was reached, through reactions involving all the various species present, a triblock copolymer was also obtained.In conclusion, this method is well suited to prepare α,ω‐diol block copolymers in which the initial oligomeric diol constitutes the center block, while the outside blocks are made of polyacetal.
Living cationic polymerization of vinyl ethers
Authors: Nuyken Oskar , Kröner Hubertus , Aechtner Stefan 
Published: March 2011

AbstractThe cationic polymerization of vinyl ethers initiated by CH3‐CH(OR)(I) / R4N+A− (R = Alkyl, A− = ClO4−, BF4−, PF6−, I−, NO3−) shows the characteristics of a living polymerization. The rate of polymerization is a function of the solvent polarity, the temperature, the type and concentration of the ammonium salt. The experimental data can be explained on the basis of the secondary salt effect overlapped by some dipol‐dipol interactions of the chain end and the added salt. Functionalization of the chain end with thermolabile azo functions yields polymeric initiator which was applied for the synthesis of blockcopolymers. Vinyl ethers functionalized with furylacrylic ester groups were polymerized and crosslinked via [2+2] cycloaddition.
Living cationic polymerization of 2‐chloroethyl vinyl ether: Kinetics, mechanism and application to polymer synthesis
Authors: Héroguez Valérie , Deffieux Alain , Fontanille Michel 
Published: March 2011

AbstractThe cationic polymerization of 2‐chloroethyl vinyl ether initiated by HI/weak Lewis acid (I2 or ZnI2) systems has been studied from both a kinetic‐mechanistic and a synthetic viewpoint. At low temperature and in toluene as solvent, the polymerization proceeds via a living process and the kinetic order with respect to monomer varies according to the nature of the Lewis acid activator. This behaviour can be explained by the coordination of the Lewis acid with both the monomer and the chain‐end, the latter leading to a strong activation of the magnified image‐I bond towards monomer insertion.The living polymerization obtained from divinylether precursors leads to magnified image‐I ended telechelics, and their transformation into dihydroxytelechelic oligomers has been performed.The chemical modification of chloroalkyl side groups by phase transfer catalysis allows the attachment of specific groups without consumption of‐OH ends.
Synthetic approaches to new polymers
Authors: Schulz Rolf C. 
Published: March 2011

AbstractA plenary lecture should be an introduction into the main topic of the symposium and a review about the state of art. Therefore, in the first part of this presentation different possibilities for the preparation of new polymers are briefly discussed from a chemical point of view. Some selected examples from the literature show how methods of organic chemistry can be utilized for polymer science: new catalytic systems, new monomers, modification of polymers, new poly‐reactions. In the second part, several polyelectrolytes are described: polymers with sec., tert. and quart. N‐atoms in the main chain, block copolymers and block polyampholytes. The third part deals with the problems of rod‐like macromolecules for instance oligo‐ and poly(p‐phenylene)s, poly(p‐phenyleneethynylene)s, aromatic polyimides and a new spiroionene.
Mesophase structure and some properties of liquid‐crystalline organoelement polymers
Authors: Plate N. A. , Antipov E. M. , Kulitchikhin V. G. 
Published: March 2011

AbstractThe structure and physico‐mechanical properties of polyphosphazene, poly(trimethylvinylsilane) and blends of polyphosphazene with polyethylene were studied. It was shown that these organoelement homopolymers form mesophase structure which can be described as condis‐crystal, and mesophase polymers are effective modifiers when mixed as blends with polyethylene, allowing to make processing more effective and obtain composites with improved mechanical properties.
The control of structure in emulsion polymerization
Authors: Lee Do Ik 
Published: March 2011

AbstractFree‐radical addition polymerization can be carried out using four different processes: mass or bulk, solution, suspension, and emulsion polymerization. Of these four processes, emulsion polymerization is unique because it is a heterogeneous process, in which the polymerization reactions can take place in three different sites: in the continuous aqueous phase, on the surface of growing particles, and within the growing particles. This unique feature of emulsion polymerization offers many possibilities for designing different polymers and latexes: e.g., high‐molecular‐weight polymers, uniform copolymers, copolymers of difficult‐to‐copolymerize monomers, functionalized (surface‐modified) latexes, uniform size latex particles, grafted latexes, and structured latexes having core‐shell, microdomain structures, interpenetrating polymer networks, etc. This paper will describe several aspects of the control of structure in emulsion polymerization.
The use of group transfer polymerization for the control of polymethacrylate molecular structure
Authors: Webster Owen W. 
Published: March 2011

AbstractThe synthesis of polymethacrylates by a repeated silyl Michael addition reaction (GTP)a allows one to control the molecular weight of the polymer by adjusting the monomer/initator ratio. A small amount of cyclic termination occurs but in general low molecular weight dispersity is obtained. Block polymers can be made by sequential addition of monomer. Functionality present on the ketene acetal portion of the initiator will be on one end of each polymer chain. Star polymers result from crosslinking active polymer with a bismethacrylate. Initiation of bismethacrylate with bisinitiator gives a ladder polymer.
Photosensitive resist system composed of phenolic resin and aromatic azide
Authors: Nonogaki Saburo , Toriumi Minoru 
Published: March 2011

AbstractPhenolic resins such as cresol novolac and poly‐(p‐hydroxystyrene) are photosensitized by the addition of an aromatic azide to give negative‐working photoresists. The spectral sensitivity can be varied from deep UV to visible region by changing the kind of azide. The system composed of poly(p‐hydroxystyrene) and a phenol ester of p‐azidobenzenesulfonic acid is expected to be useful in deep UV fine‐line lithography. The system containing 23 wt% of p‐n‐pentylphenol p‐azidobenzenesulfonate exhibits a photosensitivity about 50 mJ/cm2 at the wavelength of 248 nm.
Biologically active polymer ‐ targeting polymeric antitumor agents‐
Authors: Han Man Jung , Choi Keun Bae , Kim Ki Ho , Hahn Bo Sup , Lee Won Young 
Published: March 2011

AbstractTo synthesize targeting polymeric antitumor agents, poly[(2‐acetoxy‐3,4‐dihydro‐2H‐pyran)‐alt‐(maleic anhydride)] as polymer backbone, chlorophyll derivatives(CpD) extracted from silkworm excreta as targeting moiety and 5‐fluorouracil and 6‐mercaptopurine as pharmacons were selected. The polymer exhibited an antitumor activity comparable to that of cyclophosphamide in vivo. CpD as well as CpD‐polymer conjugate were localized on tumor cells in vitro and delivered to tumor tissues in vivo specifically. The targeting polymeric antitumor agents were synthesized by coupling pharmacons and CpD on the polymer chain with the aid of reactions between functionalities of the reactants and anhydride groups on the polymer backbone. Various tests of their biological activities in vivo are in progress.
Development of biopolymers for artificial skin substitutes and blood‐compatible materials
Authors: Kim Kea‐Yong 
Published: March 2011

AbstractIn order to develop biomedical materials we synthesized various polymers. In this study, gelatin, synthetic poly(amino acid), chitin and chitosan were chosen as the basic materials of artificial skin, polyurethane, amino acid, silicone and N‐vinyl‐2‐pyrrolidone were chosen as the basic materials of blood‐compatible materials.
The one‐dimensional intersoliton electron tunneling conduction in doped polyacetylene: Semiconductor‐metal transition
Authors: Park Y. W. , Yoon C. O. , Lee C. H. , Shirakawa H. 
Published: March 2011

AbstractThe one‐dimensional intersoliton electron tunneling conduction model in doped polyacetylene, which is a semiconductor‐metal transition mechanism, is proposed. With this model, the observed two transition concentrations (y = 0.001 and y = 0.05) can be estimated correctly. In the lightly doped regime (y < 0.001), the three‐dimensional intersoliton electron hopping conduction is dominant. At the intermediate concentration regime (0.001 < y < 0.05), the electrons (or holes dopending on the dopants) can tunnel through the pinned solitons within a single chain. These tunneling charge carriers contribute to the high conductivity. But these tunneling charge carriers can give no Pauli susceptibility since they are not band‐type carriers. Instead, they are transient carriers tunneling between the two soliton sites. Finally, in the high concentration regime (y > 0.05), the pinned soliton wave function can overlap each other forming a soliton liquid. In this stage, the bond alternation of the trans‐polyacetylene chain vanishes being equivalent to the uniform bond length chain. Therefore, the metallic conductivity and finite Pauli susceptibility are expected consistent with the observed experimental results. However, since this metallic state is formed by the soliton liquid it is not a single particle like metal. The internal vibrational modes and other signals characteristic to the soliton can persist in the metallic polyacetylene.
Recent achievements in multidimensional NMR
Authors: Griesinger C. , Brüschweiler R. , Madi Z. L. , Sørensen O. W. , Ernst R. R. 
Published: March 2011

AbstractRecent developments in high resolution multidimensional NMR spectroscopy are discussed. Emphasis is laid on the extraction of structural information especially of 3D spectra. A novel 2D experiment is proposed to measure cross relaxation induced by correlated motion in macromolecules.
Spatial structure of biomolecules by nuclear relaxation and molecular modelling methods
Authors: Rossi Claudio , Picchi Maria Pia , Marchettini Nadia 
Published: March 2011

AbstractNuclear magnetic resonance spectroscopy (NMR) has become the most frequently used technique for the investigation of the structure of biomacromolecules in solution. In particular, selective relaxation techniques have been used in the analysis of homonuclear dipolar connectivities (selective and biselective proton spin‐lattice relaxation experiments) and heteronuclear couplings (selective {H} C‐NOE, biselective carbon R1 experiments). An accurate determination of selected i‐j internuclear distances has made it possible to identify the preferred solution structure. A different experimental technique based on two‐dimensional NOE spectra has made it possible to define the complex network of dipolar interactions that exists in biomacromolecules and hence the conformational properties in solution.
Carbon‐13 NMR studies of local dynamics in polymer solutions and melts
Authors: Laupretre Françoise 
Published: March 2011

AbstractCarbon‐13 spin‐lattice relaxation time measurements have been performed at two experimental frequencies on a series of amorphous polymers in the bulk state at temperatures well above the glass‐transition temperatures and in solution. The high experimental values of the T1 minimum as a function of temperature cannot be accounted for only by the specific orientation autocorrelation functions developed for polymers. They indicate the existence of an additional fast anisotropic motion, which we have assigned to librations of limited but significant extent of the internuclear CH vectors about their rest position. Moreover, in most cases, the temperature dependence of the segmental motions proves that they are involved in the glass‐rubber transition phenomena.
Dynamic processes in aqueous protein systems. Molecular theory and NMR relaxation
Authors: Kimmich Rainer 
Published: March 2011

AbstractA model theory is presented explaining a series of striking phenomena observed with nuclear magnetic relaxation in protein systems such as solutions or tissue. The frequency and concentration dependences of the nuclear magnetic relaxation times are discussed. It is concluded that the translational diffusion of water molecules along the rugged surfaces of proteins and ‐ to a minor degree ‐ protein backbone fluctuations are crucial processes. The rate limiting factor of macromolecular tumbling is assumed to be given by the free‐water content in a certain analogy to the free‐volume model of Cohen and Turnbull. The two characteristic water mass fractions indicating the saturation of the hydration shells and the onset of protein tumbling can be related to each other on this basis. A closed and relatively simple set of relaxation formulas is presented. The potentially fractal nature of the diffusion of water molecules on the protein surface is discussed.
Nuclear magnetic relaxation and molecular motion in solid lysozyme
Authors: Fedotov V. D. , Obuchov N. P. , Spêváček J. , Straka J. 
Published: March 2011

AbstractNuclear magnetic relaxation data for both proton and carbon‐13 nuclei in solid lysozyme are analysed together to obtain information on local internal motions in protein. For this analysis the “model‐free” approach is used. Three types of internal motion appear to determine the observed nuclear relaxation in protein. They may be attributed to local rotations of methyl groups around symmetry axes, the motion of main and side chain atoms like in rigid lattice, and large‐amplitude motions of side groups (mainly, methylene groups). Conclusions on hydrated water influence on local dynamics of protein are made.
ESR imaging of polymers and solid materials
Authors: Berliner Lawrence J. , Fujii Hirotada 
Published: March 2011

AbstractEPR imaging was applied to the study of several important processes in polymers and materials. The solvent diffusion and induced swelling was visualized in the water/DMF or toluene/DMF interactions with polycarbonate or polystyrene molded rods. The cross‐sectional images revealed non‐homogeneous solute/solvent diffusion, rod expansion and crack development. The ESR lineshapes in all cases above confirmed that the nitroxide imaging agent did not interact significantly with the polymer matrix; thus the paramagnetic distribution reflected bulk solvent distribution quite well. The diffusion of an electrolyte buffer (Krebs) solution containing a nitroxide spin probe was followed in a cross‐sectional image of a polyacrylamide gel rod. A one‐dimensional radial diffusion constant was calculated for the solvent piperidinol nitroxide spin probe, TEMPOL. Lastly, solid coal rods were monitored during mild pyrolysis at 150°C in air. Here the naturally occurring organic radical composition was imaged. Even with the increase in total ESR signal and subsequent decline to ca. the initial levels, the coal rod cross‐section was essentially homogeneous in paramagnetic centers throughout the heating process. All of the imaging above utilized a homemade L‐band, flat loop surface coil spectrometer.
Charge transport in polymers studied by combining optical and electrical techniques
Authors: Bässler Heinz 
Published: March 2011

AbstractThree examples are presented demonstrating the wealth of information steady state absorption and fluorescence studies can yield regarding charge transport in polymeric systems: (i) The determination of the density of intrinsic and extrinsic hopping states in polyvinylcarbazole via site‐selective fluorescence spectroscopy by drawing on the analogy between charge and energy localization in disordered organic media, (ii) the identification of inter‐chain jumps as being rate limiting for charge transport in a polydiacetylene single crystal as an example for conjugated polymers and (iii) the elucidation of polaron formation in phenylenevinylene‐type polymers.
Magnetic spin effects as a tool for studying electronic processes in solids
Authors: Frankevich E. L. 
Published: March 2011

AbstractThe role played by the law of the conservation of momentum in the primary processes of charge carrier generation is considered. External magnetic field is shown to be able to influence the rate constants governing spin dependent processes. Magnetic field effect and Reaction Yield Detected Magnetic Resonance on the photoconductivity of organic solids give important information on the mechanism of primary steps of charge photogeneration.
Mechanism of photogeneration of free carriers in quasi‐one‐dimensional photosemiconductors: Application tc polydiacetylene
Authors: Frankevich E. L. , Sokolik I. A. , Lymarev A. A. 
Published: March 2011

AbstractThe dependence of the quantum yield of free charge carriers on the electric field strength in quasi‐one‐dimensional photosemiconductors is rationalized. The occurrence of the trapping and nongeminate recombination in the bulk of the material is shown to be responsible of nonzero yield at zero external field. Current i vs. excitation intensity g plot obeys the law i∼g2/3 for polydiacetylene single crystal as expected from theory presented.