bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymer‐bound bulky‐phosphite modified rhodium hydroformylation catalysts
Authors: van Leeuwen Piet W.N.M. , Jongsma Tjeerd , Challa Ger 
Published: March 2011

AbstractAttachment of phosphites to styrene copolymers is described which are used as rhodium hydroformylation catalysts. The influence of the chain loading on the activity and complex formation of three types of copolymer‐bound rhodium hydroformylation catalysts in comparison with their low molecular weight analogues has been studied. The catalytic activity of the polystyrene‐bound system with the most bulky phosphite, the first system studied, is identical to that of the low molecular weight analogue. The catalysts show a high activity towards the hydroformylation of the otherwise unreactive cyclooctene. It was found that only one phosphite is coordinated to the rhodium complex in its active form. An equilibrium between this complex and an inactive complex without phosphite ligands prohibits its use in continuous flow reactors.Secondly, as polymer support a perfectly random copolymer of styrene and less bulky 3,3′,5,5′‐tetra‐tert‐butylbiphenyl‐2,2′‐diyl p‐vinylphenylphosphite was used. The chain loading α of this copolymer with phosphite ligands has a large influence on the complex formation of the catalyst. With high chain loadings moderately active bis‐phosphite catalysts are formed. Low chain loadings give active, easily accessible, monophosphite complexes. The active species in the hydroformylation of sterically hindered alkenes is a mono‐phosphite rhodium complex. The activity of the copolymer‐bound catalyst towards the hydroformylation of cyclooctene is found to be as high as the activity of its low molecular weight analogue. For styrene, this polymer catalyst yields a slower catalyst than the low‐molecular weight analogue.The third part demonstrates that silica‐grafted polymer‐bound phosphite modified rhodium complexes can be used in continuous flow reactors. The hydroformylation of styrene was carried out at moderate pressure (pCO/H2 = 3 MPa) and temperature (T = 100°C), yielding constant conversions over a period of at least ten days. These positive results were obtained in benzene as a solvent and for a ligand to rhodium ratio of only four.
Complexing polymer sorbents and metal polymer complex catalysts with specially designed structure of active centres
Authors: Efendiev A. A. 
Published: March 2011

AbstractA new approach to a problem of preparation, regulation of properties and formation of three‐dimensional structure of complexing polymer sorbents and metal polymer complex catalysts with specially designed structure of active centres has been developed. The main principle is based on the use of “memory” of polymer composition and consists in prearrangement of macromolecules of initial complexing polymer or metal polymer complex catalyst to sorbing metal or hydrocarbon substrate followed by fixation of optimum for particular substrate conformation by intermolecular crosslinking. Using this principle a number of crosslinked complexing polymer sorbents and metal polymer complex catalysts containing phosphorylic, carboxylic, pyridine, amine and imine functional groups have been prepared. It has been shown that prearrangement leads to essential improvement of basic sorption and catalytic properties of the crosslinked complexing polymers ‐ sorption capacity, the rate of uptake, selectivity and catalytic activity.
Electrochemical quartz crystal microbalance studies of redox polymer films
Authors: Robert Hillman A. , Loveday David C. , Glidle Andrew , Vos Johannes G. , Clarke Alan P. , Kelly David , Bruckenstein Stanley 
Published: March 2011

AbstractElectrochemical quartz crystal microbalance measurements are reported for redox switching of thin films of three macromolecule‐metal complexes: poly(vinylferrocene) (PVF), 10% osmium‐functionalized poly(vinylpyridine) (Os‐PVP), and 10% osmium functionalized poly(vinylpyridine‐co‐styrene) (Os‐PVP‐co‐PS). The data provide insight into the ion and solvent transfer processes associated with electron transfer between the electrode and the electroactive film. Four important parameters are identified: electrolyte composition, (co)polymer composition, prior film history and experimental time scale.
Electrochemistry and electrochromic properties of phenanthroline‐iron(II/III) complex films
Authors: Oyama Noboru , Kitagawa Mako , Inaba Hiroshi , Kawase Kazuya 
Published: March 2011

AbstractNew films of the iron complexes with bis((2‐hydroxyphenyl)methylaminosulfonyl)bathophenanthroline(HPBP) and bis((2‐aminophenyl)methylaminosulfonyl)bathophenanthroline(APBP) ligands are prepared on the electrode surfaces by electrochemical polymerization. The resulting film‐coated electrode shows a well‐defined reversible voltammogram corresponding to the redox reaction of the Fe(II/III) complexes and an electrochromic change from red(absorption maximum: 540 nm) to colorless. The response rate of the color change to a potential step was found to be correlated to the apparent diffusion coefficient(Dapp) for the homogeneous charge‐transport process within the film. The Dapp values estimated are (3‐4) × 10−9cm2s−1 for the [Fe(APBP)3] film and(1‐2) × 10−8cm2s−2 for the [Fe(HPBP)3] film, respectively, by potential‐step chronoamperometric and chronocoulometric methods. The result of electrochemical quartz crystal microbalance(EQCM) measurements4) and dependence of the formal potential of the metal complex of the Fe(II/III) redox couple with activity of the supporting electrolyte anion in NaClO4 aqueous solution showed that anion, cation, and solvent move simultaneously across the polymer film/solution interface during the redox reaction. A piezoelectric admittance measurement4) of the poly[Fe(APBP)3] coated quartz crystal electrode showed that the viscosity of the film is affected by the oxidation state of iron.
Theory of polymer melts and applications
Authors: Des Cloizeaux J. 
Published: March 2011

AbstractThe theory of polymer melts is founded on the process of double reptation for high masses and long times, and on simple Rouse relaxation for low maases and short times. In order to describe the intermediate region, these two different principles have to be combined, and we show how this can be done. However, pure reptation is modified under the influence of an effect which cannot be reduced to the Rouse elasticity of polymers, and this effect could be calculated by mode‐mode coupling.
Equilibrium and dynamical properties of gaussian stiff chain molecules
Authors: Winkler Roland G. , Harnau Ludger , Reineker Peter 
Published: March 2011

AbstractWe present a novel analytically tractable model for stiff chain molecules. The equilibrium distribution function of the chain is derived using the maximum‐entropy principle. For that purpose, we first formulate a discrete chain model, where the connections of the points and the restriction on bending are taken into account via constraints. We then perform the limit to a continuous chain and show that the mean‐square end‐to‐end distance and the radius of gyration of the continuous chain are identical with the same quantities of the Kratky‐Porod wormlike chain. The dynamics of our chain is investigated in dilute solution without hydrodynamic interactions. The linear dynamical equation is solved by a normal mode analysis. We discuss the dependence of the relaxation times on the single parameter of the model, the persistence length. For small persistence lengths we obtain the well known relaxation times of the Rouse model. In the stiff‐chain limit, we find the pure bending relaxation times and, in addition, the rotational relaxation time.
Dynamics of star polymers
Authors: Guenza Marina , Perico Angelo 
Published: March 2011

AbstractStatic and dynamic properties of star polymers in theta solutions are derived for semiflexible and the partially stretched (PS) arm models. The extension of the Optimized Rouse‐Zimm approach to describe the local dynamics (ORZLD) of star polymers is presented, together with some results for static and dynamic structure factors.
Molecular dynamics simulation studies of a complex fluid ‐solid interface ‐ the benzene‐alkane‐graphite system
Authors: Hentschke Reinhard , Kotelyanskii Michael J. , Winkler Roland G. 
Published: March 2011

AbstractInterfaces between solid surfaces and solutions are of considerable scientific as well as technological interest, in particular in the context of the adsorption and the formation and organization of molecular films. The realistic modeling of such complex interfaces on the molecular scale is an important testing ground for simulation techniques. Here we focus on the benzene‐alkane‐graphite interface as an example of the above class of systems, including surface induced segregation, adsorption, and structural aspects of the graphite‐solution interface.
Polymer crystallization: Simulation with entropic barrier model and application to specific polymers
Authors: Goldbeck‐Wood Gerhard 
Published: March 2011

AbstractThe growth of polymer single crystals has been simulated on the basis of a simple two‐dimensional ‘entropic barrier’ model. The chain is described by a sequence of growth units. Their additions and removals are determined by rate constants obeying detailed balance. The crystallization is then simulated by a kinetic Monte Carlo algorithm. An application of the model to specific crystallizable polymers (polyethylene, isotactic polystyrene, isotactic polypropylene, polyhydroxybuterate and polypivalolactone) is presented. Input parameter values for the model are derived from the respective surface free energies, bulk enthalpies, melting points and crystallographic repeat lengths. The only free parameter is the length of a polymer growth unit. This is set to half the lamellar crystal thickness at large undercooling. The lamellar thicknesses calculated on this basis are in good agreement with experimental data. An analysis of the growth unit lengths of the different polymers indicates a scaling with the chain persistence length in the melt.
Models for cracking of polymer coatings
Authors: Sokolov Igor M. , Morgenstern Olaf , Blumen Alexander 
Published: March 2011

AbstractWe investigate the dynamics of cracking of a brittle coating covering an elastically stretched substrate. We consider here a scalar model (an electrical analogue) in order to describe fractures in thin and in thick films. The model captures the essential features of the fragmentation of coatings and allows us to classify different temporal regimes in the cracking process and to obtain several basic patterns of the cracks' morphology.
Prediction of polymer miscibility from molecular mechanics calculations
Authors: Gorella Boris , Tiller Andrew R. 
Published: March 2011

AbstractA new computational method is presented for the rapid estimation of polymer miscibility. The algorithm (coined FLEXIBLEND) uses molecular mechanics calculations on a pair of polymer segments and takes into account the effects of local chain flexibility to estimate heats of mixing. This paper shows miscibility predictions in agreement with experiment for blends of poly(ethyleneoxide) (PEO) with isotactic poly(propylene) (PP) as an immiscible system and of PEO with poly(acrylic acid) (PAA) as a miscible system.
Simulation study of poly(γ‐benzyl‐l‐glutamate) in dimethylformamide
Authors: Helfrich Jürgen , Hentschke Reinhard , Apel Ute 
Published: March 2011

AbstractWe perform atomistic Molecular Dynamics simulations of Poly(γ‐Benzyl‐L‐Glutamate) (PBLG) in Dimethylformamide (DMF) to study the structure and some dynamic aspects of the complex side chain ‐ solvent interface. In addition, we investigate the elastic behavior of PBLG with the emphasis on the determination of the persistence length.
Md‐simulation of α‐keratin intermediate filaments
Authors: Knopp Birgitta , Jung Bernd , Wortmann Franz‐Josef , Höcker Hartwig 
Published: March 2011

AbstractIn recent years powerful computer systems have become readily accessible to simulate complex chemical problems. Based on the primary structure of the intermediate filament monomer unit of wool, small sequences are selected. Their molecular dynamic behaviour is simulated, in order to investigate the secondary and tertiary structure as well as their stability.The simulations are carried out for a helical segment and a linker segment, selecting the ideal α‐helix as start conformation. In vacuum all simulations show an unstable α‐helix due to shifts of the intrahelical hydrogen bonds. So a new helical structure with a larger helix diameter is formed. However in simulations with surrounding water the α‐helix remains stable throughout the simulation time. Up to now it has not been possible to dectect any fundamental difference in the molecular dynamic behaviour of the helical and the linker segment.
Synthesis, structure and properties of fluorinated graphite
Authors: Nakajima Tsuyoshi 
Published: March 2011

AbstractFluorine‐graphite intercalation compounds, C2F to C16F were synthesized by various methods. C‐F bonds range from ionic to semi‐covalent. These properties of C‐F bonding give to fluorinated graphite metallic conductivity, higher hydrophilicity than graphite and high reduction potential. The c‐axis and in‐plane structures are governed by C‐F bonding, fluorine intercalation rate and host graphites.
A comparison of the properties of methacrylate polymers derived from racemic and homochiral monomers containing a trifluoromethyl group at a tertiary stereogenic centre
Authors: O'Hagan David , Zaidi Naveed A. 
Published: March 2011

AbstractThree homochiral CF3 containing methacrylate esters have been prepared, and polymerised with butyllithium at ‐78°C. Melting points, gel‐permeation chromatography, differential scanning calorimetry and X‐ray powder diffraction analyses of the resulting polymers have been compared to those of their racemic counterparts. It is clear that the homochiral monomers give rise to largely crystalline methacrylates whereas the racemic monomers generate amorphous materials.
Fluoroacrylic esters and related monomers: Preparation and use as synthons
Authors: Wakselman Claude 
Published: March 2011

AbstractPreparations of acrylic compounds substituted by fluorine atoms or trifluoromethyl groups at the a or β positions are reviewed. Their use in Michael additions, annelation reactions and Diels‐Alder condensations leads to more complex molecules, such as fluorinated analogues of natural products.
Photoaddition reactions of fluoroolefins with diols and cyclic ethers
Authors: Paleta O. , Církva V. , Kví čala J. 
Published: March 2011

AbstractFluoroalkylation of aliphatic diols, tetrahydrofuran and 1,3‐dioxolanes with perfluoroolefins under photochemical initiation was studied. The aim of the study was the preparation of fluoroalkylated diols as intermediates for special fluorinated monomers. Fluoroalkylation was only partly successful in the case of 1,4‐butanediol and quite successful with tetrahydrofuran and 2,2‐dimethyl‐1,3‐dioxolane. The fluoroalkyl diols obtained were converted to monomethacrylates that are amphiphilic monomers.
The preparation and thermal dimerization study of a trifluorovinyl‐containing imide. Application to the synthesis of a trifluorovinyl‐containing polyimide precursor
Authors: Yamomoto Michiharu , Swenson Dale C. , Burton Donald J. 
Published: March 2011

AbstractElaboration of 2‐fluoro‐α,β,β‐trifluorostyrene 7, prepared by the palladium catalyzed coupling reaction of l‐fluoro‐2‐iodobenzene with a trifluorovinylzinc reagent, yielded the trifluorovinyl‐containing imide 1. Thermal dimerization of 1 at 140‐160°C leads predominately to the corresponding E‐cyclobutane 12, whose structure was established by x‐ray crystallography. Similar methodology was utilized to prepare 2,2‐bis{4‐[4‐amino‐2‐(l,2,2‐trifluoroethenyl)phenoxy]phenyl)hexafluoropropane 19, a precursor to the trifluorovinyl‐containing polyimide 18.
New strategies for synthesis of partially fluorinated heterocycles as precursors for trifluoromethyl‐substituted polymers
Authors: Burger Klaus , Helmreich Brigitte , Jendrewski Oliver , Hecht Reinhold , Maier Gerhard , Nuyken Oskar 
Published: March 2011

AbstractThe building‐block strategy is applied to the synthesis of new compounds with two five‐membered heteroaromatic units. The heteroaromatic rings contain a fluorine atom which is activated towards nucleophilic displacement reactions by an adjacent trifluoromethyl group. The difunctional compounds can be converted into poly(arylene ether)s by base‐catalyzed polycondensation with bisphenols or bisthiophenols. Trifluoromethylated poly(arylether oxazole)s and poly(arylthioether oxazole)s are obtained by this route. All representatives of these two new classes of polymers are soluble in common organic solvents. Reaction conditions for the polycondensation as well as thermal stability, glass transition temperatures, and molar masses of the polymers are described.
Macromolecular design of cationic polyelectrolytes on the chitosan basis for achievement of high antimutagenic efficiency at gamma‐irradiation
Authors: Alexandrova V.A. , Ryzhkov D.V. , Obukhova G.V. , Domnina N.S. , Topchiev D.A. , Kǒtlyarova E.B. , Shevchenko V.A. 
Published: March 2011

AbstractA new approach to the problem of construction of efficient antimutagenic (at γ‐irradiation) systems has been developed on the basis of the models‐ synthetic cationic polyelectrolytes‐ polyquaternary salts of diallyldimethyl‐ammonium type.
Molecular design of biologically active biodegradable polymers for biomedical applications
Authors: Lee Keun‐Ho , Chu Chih‐Chang , Quimby Fred , Klaessig Suzanne 
Published: March 2011

AbstractThe objective of this research is to synthesize synthetic biodegradable polymers that would have biological functions similar to nitric oxide. Polyglycolide (PGA) was the synthetic biodegradable polymer and 4‐amino‐2,2,6,6‐tetramethylpiperidine‐1‐oxy (Tempamine) was chosen as the source of nitroxyl radicals. Tempamine nitroxyl radicals were chemically incorporated into the carboxylic acid chain ends of PGA macromolecules via amide linkage. The kinetics of in vitro hydrolytic release of Tempamine nitroxyl radicals from the host PGA in buffered media at 37 °C was studied. Tempamine nitroxyl radicals were released into the media via cleavage of either ester linkages in the PGA segments or/and the amide linkage between Tempamine and the PGA segments. The duration of hydrolysis would determine the type of degradation products that were different in the segmental length of the PGA component. A preliminary in vitro cell culture study of this new generation of biologically active biodegradable polymers indicated that it was able to retard the proliferation of smooth muscle cells as pure nitric oxide does.
Synthesis and characterization of aliphatic poly(esteramide)s containing symmetrical bisamide blocks
Authors: Stapert Henk R. , Dijkstra Pieter J. , Feijen Jan 
Published: March 2011

AbstractA series of symmetrical diols were synthesised through ring‐opening of lactones with different ring sizes by alkane diamines in moderate to good yields. Ring‐opening of the dilactones glycolide and lactide with a diamine in equimolar amounts afforded symmetrical diols in quantitative yield.Aliphatic poly(ester‐amide)s were prepared by polycondensation of N,N′‐bis(caproyl)butane diamide, dimethyl adipate and 1,4‐butanediol. The structure of the diamide was retained in the polymer. The polymers synthesized are semi‐crystalline materials that possess ordered structures in the solid phase over almost the entire copolymer range. Depending on thermal history and copolymer composition thermal analyses is in agreement with the presence of pseudo‐hexagonal crystal structures below 75°C, a fast melting recrystallization at this temperature and a triclinic structure at higher temperatures.
Synthesis path versus distribution of functional groups in cellulose ethers
Authors: Liebert TIM , Heinze THOMAS 
Published: March 2011

AbstractDifferent ways for carboxymethylation of cellulose are discussed exemplary for cellulose ether synthesis in terms of the resulting structural features. The industrially applied slurry process yields polymers with statistic amounts of the four differently substituted repeating units glucose, mono‐, di‐, and tri‐O‐carboxymethylglucose. Surprisingly, the newly developed totally homogeneous carboxymethylation in the efficient cellulose solvent Ni[tris(2‐aminoethyl)amine](OH)2 gives exactly the same result. Thus, the polymer is evenly accessible during both reaction paths. In contrast the carboxymethylation starting from homogeneous solutions of cellulose in N,N‐dimethyl acetamide /LiCl or solutions of reactive derivatives of cellulose in dimethyl sulfoxide (DMSO) yields polyelectrolytes with a nonstatistic content of the building units. This is achieved via an induced phase separation forming highly reactive microstructures.
Novel ring‐opening polymerization of lactide by lipase
Authors: Matsumura Shuichi , Mabuchi Kimihiro , Toshima Kazunobu 
Published: March 2011

AbstractSix‐membered D,L‐, L,L‐ and D,D‐lactides were polymerized by lipase over a temperature range of 80 to 130 °C to yield the polylactide with a molecular weight (Mw) of greater than 270000. Among the lipases tested, lipase PS gave the greatest molecular weight of polylactide. The polymerization of D,L‐lactide by lipase was better than that of L,L‐ and D,D‐lactides. The polymerization of lactide by lipase showed the characteristic features, such as induction period for the initiation of polymerization, formation of oligomer and subsequent formation of high molecular weight polylactide, which may imply the characteristic polymerization by lipase. Immobilization of lipase on celite significantly enhanced the polymerization of lactide particularly with respect to the low concentration of the enzyme and the Mw of the resultant polymer. It was found that there is no clear relationship between enzymatic polymerizability and enzymatic degradability with respect to the enzyme origin and the stereochemistry of lactide.
Ring‐opening polymerization of degradable polyesters
Authors: Stridsberg Kajsa , Gruvegård Mats , Albertsson Ann‐Christine 
Published: March 2011

AbstractMedium to high molecular weight random copolymers of 1,5‐dioxepan‐2‐one (DXO) and L‐lactide (L‐LA) or ε‐caprolactone (ε‐CL) of different compositions have been investigated. Polymerization was conducted in bulk at 110°C using stannous 2‐ethylhexanoate as catalyst. Poly(DXO‐co‐L‐LA) is a hydrolysable material with a glass transition temperature (Tg) ranging from −36 up to 58°C depending on the molar composition. The material exhibited crystallinity as long as the amount of DXO did not exceed 50 weight%. Reactivity ratios were determined to rL‐LA=10 and rDXO=0.1, giving a more blocky structure than expected in a random copolymer. The copolymer between ε‐CL and DXO was shown to be a truly random copolymer by 13C NMR, as expected from the reactivity ratios, rDXO=1.6 and rε‐CL=0.6. Tg of the material was ranging from −64 up to −39°C. The ability of the poly(DXO‐co‐ε‐CL) to crystallize was retained up to a DXO content of 40 weight%. The melting temperature and crystallinity of both copolymers decrease with increasing amount of DXO. Incorporation of semicrystalline comonomers, L‐LA or ε‐CL, into the amorphous poly(DXO) creates materials with adjustable properties depending on the molar composition.
Amphiphilic graft copolymers ‐ preparation and interfacial properties
Authors: Wesslén Bengt 
Published: March 2011

AbstractAmphiphilic graft copolymers containing poly(ethylene oxide) (PEO) grafts have been prepared by various methods, for example, by coupling of reactive hydrophobic backbone polymers with end‐functionalised PEO, by macromonomer copolymerisation, and by anionic graft polymerisation of EO onto polymer backbones carrying functional groups as initiator precursors. The graft copolymers are amphiphilic and were shown to accumulate at surfaces and interfaces in solution and in the solid state. Amphiphilic starch derivatives were prepared by reaction of amylose and starch with aliphatic α‐epoxides.