bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and surface characterization of a new multiblock copolymer based on poly(dimethylsiloxane) and aromatic polysulfone
Authors: Di Pasquale Giovanna , La Rosa Angela , Mamo Antonino 
Published: April 2003

AbstractA new alternating block copolymer was synthesized from dihydroxy‐terminated poly‐(ether ketone sulfone) and bis(dimethylamino)‐terminated polydimethylsiloxane oligomers. The chemistry and the thermal properties are discussed. Surface chemical composition of films was analyzed by ESCA. Quantitative calculations showed a noticeable siloxane enrichment at the surface.
Preparation of new poly(ester‐imide)s with cyanoazobenzene side chains generating optical phase‐conjugate signals
Authors: Sato Moriyuki , Nakagawa Kazuo , Tada Yuji , Ujiie Seiji 
Published: April 2003

AbstractNew semi‐rigid poly(ester‐imide)s with cyanoazobenzene side chains were prepared by melt polycondensation of a diethyl isophthalate derivative of cyanoazobenzene with N, N′‐dihexanols of five aromatic diimides in the presence of zinc acetate. Differential scanning calorimetry (DSC) measurements and polarizing microscope observations demonstrated that the polymers have glass transitions (Tg) between 46 and 93°C and show no liquid crystalline (LC) properties. All poly(ester‐imide)s generated optical phase‐conjugate (PC) signals at high reflectivity by degenerate four‐wave mixing (DFWM) at low pump‐beam power.
Intermolecular chain transfer to polymer with chain scission: general treatment and determination of kp/ktr in L,L‐lactide polymerization
Authors: Baran Jolanta , Duda Andrzej , Kowalski Adam , Szymanski Ryszard , Penczek Stanislaw 
Published: April 2003

AbstractA general kinetic treatment of the system with intermolecular chain transfer followed by fast reinitiation is given. It leads to the broadening of the molecular weight distribution (MWD), the number of growing chains being invariable. Thus, this system can be considered as a special case of living polymerization. A general method has been elaborated allowing the determination of the ratio of the rate constant of propagation (kp) to the rate constant of the bimolecular transfer (k(2)tr) from the dependence of the MWD on monomer conversion. Numerical values of kp/k(2)tr equal to ≈ 102 and 25 were thus determined for the polymerization of L, L‐lactide (L, L‐dilactide) initiated with aluminium tris(isopropoxide) trimer ({Al(OiPr)3}3) and tributyltin ethoxide (nBu3SnOEt), respectively.
Novel core‐shell type thermo‐sensitive nanoparticles composed of poly(γ‐benzyl L‐glutamate) as the core and poly(N‐isopropylacrylamide) as the shell
Authors: Cho Chong‐Su , Cheon Jae‐Bok , Jeong Young‐Il , Kim In‐Sook , Kim Sung‐Ho , Akaike Toshihiro 
Published: April 2003

AbstractAB diblock copolymers consisting of PBLG as the hydrophobic part and PNIPAAm as the hydrophilic one were prepared by polymerization of BLG‐NCA with semitelechelic PNIPAAm with amino end group as initiator. The core‐shell type nanoparticles of the block copolymers were obtained by the diafiltration method. The sizes of the nanoparticles were from about 73 to 359 nm and the shapes of them were spherical. The release for indomethacin (IN) from the nanoparticles was faster at 28°C than at 34°C due to the conformational change of PNIPAAm by temperature.
Electron transfer between two stable radicals
Authors: Zheng Haipeng , Zhang Ruifeng , Dong Fengxia , Zheng Yingguang , Shen Jiacong 
Published: April 2003

AbstractElectron spin resonance (ESR) is a sensitive tool to detect the electron‐transfer processes in some specified systems from the change of the ESR signals. In this paper, the interaction between poly(N,N‐dimethylaniline) (PDMA) and 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) was investigated by ESR spectra based on the stability of their radicals in ethanol. It is shown that an electron‐transfer process occurs from nitrogen atoms of PDMA molecules to those of DPPH molecules which makes PDMA form more stable radical cations and eliminates the radicals on DPPH.
Synthesis and characterization of star‐shaped polytetrahydrofuran
Authors: Van Caeter Peter , Goethals Eric J. 
Published: April 2003

AbstractStar polymers of tetrahydrofuran (polyTHF) were prepared by reaction of living polyTHF with diethylene triamine (DETA) in the presence of 2,2,6,6‐tetramethylpiperidine (TMP) as proton trap. The influence of several reaction parameters on the end‐capping reaction was studied in order to produce stars having varying number of arms. With a starting living polyTHF with a molecular weight of 1600, star‐shaped polymers containing up to seven polymer chains could be prepared. When the molecular weight of the living polyTHF was 8000, at most five polymer chains could be grafted on the DETA. Some physical properties of the star polymers were compared with those of their linear counterparts of the same molecular weight.
Efficient synthesis and facile polymerization of some cyclic bisphenol o‐phthalates
Authors: Jiang Hongyan , Chen Tianlu , Xu Jiping 
Published: April 2003

AbstractA series of new macrocyclic aromatic esters have been efficiently synthesized from o‐phthaloyl dichloride and various bisphenols, and unambiguously characterized by a combination of GPC, MS(FAB), FTIR and NMR. These macrocyclic oligomers undergo facile ring‐opening polymerization in the presence of anionic initiators to give high molecular weight polyarylates.
Synthesis of linear and three‐arm star tert‐chlorine‐telechelic polyisobutylenes by a two‐step conventional laboratory process
Authors: Feldthusen Jesper , Iván Béla , Müller Axel H. E. , Kops Jørgen 
Published: April 2003

AbstractA two‐step conventional laboratory process was developed for the synthesis of mono‐ and difunctional linear and three‐arm star tert‐chlorine‐telechelic polyisobutylenes (PIB) with desired molecular weights (MW) and narrow molecular weight distribution (MWD) by living carbocationic polymerization (LCCP). This polymerization method applies easy to handle operations and chemicals. LCCP of isobutylene (IB), was carried out in CH2Cl2 as solvent and with BCl3 as coinitiator in the first step to obtain soluble low MW PIB prepolymer with narrow MWD. This was followed by addition of hexane, TiCl4 and additional monomer in the second step to prepare PIBs with desired MW and narrow MWD in practically any suitable MW region. Comparison of the one‐step and two‐step processes is also described.
Cyclic carbonates, novel expandable monomers on polymerization
Authors: Takata Toshikazu , Sanda Fumio , Ariga Toshiro , Nemoto Hideo , Endo Takeshi 
Published: April 2003

AbstractA variety of cyclic carbonates was shown to undergo volume expansion on polymerization. The degree of volume expansion, which was measured by the density gradient tube method, was ranging from 1.1% to 7.7%. The volume expansion was examined by assuming a change in molecular interaction such as dipole moment between monomer and polymer states.
Preparation of monodisperse polymer particles from 4‐vinylpyridine
Authors: Takahashi Kazuhiko , Miyamori Shigeo , Uyama Hiroshi , Kobayashi Shiro 
Published: April 2003

AbstractDispersion polymerization of 4‐vinylpyridine was performed by using polystyrene‐block‐polybutadiene as stabilizer in a mixture of N,N‐dimethylformamide (DMF) and toluene to produce polymer particles. The weight ratio of the solvents affects the particle size and dispersity. In the range of DMF content from 5 to 20 wt.‐%, uniform particles of a diameter of ca. 1 μm were obtained. The present system was expanded to the preparation of monodisperse particles of poly[(4‐vinylpyridine)‐co‐(methacrylic acid)].
Synthesis of polysilanes by reductive coupling of dichlorosilanes mediated with alkali metal/crown ether supramolecular complexes in a homogeneous system
Authors: Jedliński Zbigniew J. , Kurcok Piotr , Nozirow Farhod 
Published: April 2003

AbstractStructure and properties of poly(methylphenylsilane) synthesized by reductive coupling of silyl halides with alkali metal supramolecular complexes: (Mt+/18‐crown‐6, Mt−, where Mt = K, Na; 18‐crown‐6 = 1,4,7,10,13,16‐hexaoxacyclooctadecane) were investigated. The coupling process yields polymers exhibiting narrow molecular weight distribution and number‐average molecular weights up to 8 500, cyclic oligomers being formed along with linear ones.
Synthesis and properties of hydrophilic polymers, 6. Water‐soluble polypyrrole graft copolymers with electrical conductivity
Authors: Geckeler Kurt E. , Arsalani Nasser , Rivas Bernabé L. 
Published: April 2003

AbstractA novel method for the preparation of water‐soluble polypyrrole graft copolymers with polyamines or polyimines is described. The polyreaction is performed in acidic solution by using chemical oxidants, e.g. iron(III) chloride or ammonium peroxodisulfate. The graft copolymers showed electrical semiconductivity in the undoped state which can be placed between the high conductivity of polypyrrole and the nonconductivity of the polyimine. Their thermal stability at 250°C is improved compared to polypyrrole. The novel graft copolymers are soluble in water over a wide pH range and have a good processability.
A new approach for the fabrication of an alternating multilayer film of poly(4‐vinylpyridine) and poly(acrylic acid) based on hydrogen bonding
Authors: Wang Liyan , Wang Zhiqiuang , Zhang Xi , Shen Jiacong , Chi Lifeng , Fuchs Harald 
Published: April 2003

AbstractA new approach for the fabrication of a multilayer film assembly is explored, which is based on the alternating assembling of poly(4‐vinylpyridine) and poly(acrylic acid) via hydrogen bonding. The homogeneous multilayer films were characterized by UV‐Vis, X‐ray diffraction and atomic force microscopy (AFM) measurements. The nature of interaction between the two polymers is identified as hydrogen bonding by IR spectroscopy.
Interfacial tension of demixed polymer solutions: augmentation by polymer additives
Authors: Schneider Anja , Wolf B. A. 
Published: April 2003

AbstractThe interfacial tension between phase separated polymer solutions increases pronouncedly upon the addition of small amounts of incompatible polymers. This feature is demonstrated by means of measurements with solutions of polystyrene in cyclohexane and the following additives: poly(styrene‐block‐dimethylsiloxane), polyisobutylene and polydimethylsiloxane. Theoretical considerations based on a correlation between the lengths of tie lines and the corresponding interfacial tension corroborate this finding.
Composites 3. Reinforcement of biodegradable matrices by helical polypeptides
Authors: Kricheldorf Hans R. , Wahlen Lars , Chen Khezi 
Published: April 2003

AbstractBlends of poly(ε‐caprolactone) as the matrix material and 1,2,4, or 8 wt.‐% of a poly‐peptide were prepared by dissolution in a cosolvent and coprecipitation into cold methanol. A low‐and a high‐molecular‐weight poly(γ‐benzyl L‐glutamate), a poly(γ‐methyl L‐glutamate) and a poly(D,L‐phenylalanine) were used as reinforcing components and compared with a liquid‐crystalline (LC) polyester derived from a double‐substituted terephthalic acid. Films of all blends were subjected to stress‐strain measurements. A weak reinforcing effect was found for the poly(γ‐benzyl L‐glutamate)s, a somewhat stronger influence for the other polypeptides and the strongest effet for the LC‐polyesters 1.
Deorientation effects on extrusion rheometry of a thermotropic copolyester
Authors: Tormes Marta , Muñoz María Eugenia , Santamaría Anton 
Published: April 2003

AbstractExtrusion rheometry experiments with a commercial thermotropic liquid crystalline copolyester show concave Bagley plots and convex pressure profiles. A loss of the orientation produced at the entrance of the capillary and the slit can explain these non‐linearities. Assuming that the order parameter, S, relaxes exponentially with time, the Doi‐Edwards model for the shear flow of rod‐like polymers is used to adjust experimental data.
Studies towards a tailor‐made catalyst for the Diels‐Alder reaction using the technique of molecular imprinting
Authors: Liu Xiao‐Chuan , Mosbach Klaus 
Published: April 2003

AbstractA tailor‐made catalytically active polymer catalyzing the bimolecular Diels‐Alder reaction is described. Kinetic studies carried out in acetonitrile at 82°C show a 270‐fold rate acceleration (kcat/kuncat) for the Diels‐Alder reaction between tetrachlorothiophene dioxide and maleic anhydride. The imprinted polymer induces Michaelis‐Menten kinetics, with an apparent Km of 42.5 mM and an apparent kcat of 3.82 × 10−2 min−1, respectively. Substrate selectivity, accessible binding site analysis, dissociation constant determination, and inhibition study were also performed.
Polyolefins with high glass transition temperatures
Authors: Henschke Olaf , Köller Frank , Arnold Manfred 
Published: April 2003

AbstractThe copolymerization of propene and norbornene with the isospecific metallocene catalyst dimethylsilylenebis(η5‐inden‐1‐yl)zirconium dichloride/methylaluminoxane ((CH3)2Si[Ind]2ZrCl2/MAO) was investigated. Because of the surprisingly high reactivity of the cyclic olefin copolymers with a norbornene content of 11 mol‐% up to 98 mol‐% were synthesized. The resulting copolymers are amorphous. The glass transition temperatures studied by differential scanning calorimetry measurements increase with rising norbornene content in the copolymer. High glass transition temperatures of Tg > 240°C were found for the copolymers with the highest content of norbornene.
Ethylene polymerizations with novel tantalum(V) aminopyridinato complex/MAO systems
Authors: Hakala Kimmo , Löfgren Barbro , Polamo Mika , Leskelä Markku 
Published: April 2003

AbstractThe use of two kinds of tantalum(V) aminopyridinato complexes, bis(2‐benzylaminopyridinato)trichlorotantalum(V) and trichlorobis[2,6‐di(phenylamino)pyridinato‐N,N′]‐tantalum(V), activated by methylaluminoxane was studied in polymerization of ethylene. The activities of these homogeneous catalyst systems are comparable to those of metallocenes. The weight‐average molecular weights (M̄w) of the produced polyethylenes are between 60 000 and 200 000 and M̄w/M̄n ≈ 2.
Vinylic polymerization of norbornene by Pd(II)‐catalysis in the presence of ethylene
Authors: Haselwander T. F. A. , Heitz W. , Maskos M. 
Published: April 2003

AbstractPd(II) catalysts with nitrilo ligands and BF4− counter ions give the best results in vinylic polymerization of norbornene. Absolute molecular weight determination of polynorbornene (PN) by means of light scattering and the three‐dimensional shape of PN were also investigated. By correlation of molecular weights M̄w with intrinsic viscosity (Staudinger‐index) [η], yield a close to 0.5 exponent for the Mark‐Houwink equation with solvents chlorobenzene and cyclohexane at 25°C expected for polymer molecules with confined conformation. The vinylic polymerization of norbornene with [(CH3CN)4Pd][BF4]2 (I) in nitromethane in the presence of ethylene results in PN with narrow molecular weight distribution. No termination and transfer reactions were found, nor any incorporation of ethylene could be detected.
Effect of crystal‐disrupting chlorohydroquinone on the first‐order transitions of poly(aryl ether ketone)s containing biphenyl units
Authors: Zhang Shanju , Zheng Yubin , Wu Zhongwen , Tian Mingwen , Yang Decai , Yosomiya Ryutoku 
Published: April 2003

AbstractThe novel poly(aryl ether ketone)s were synthesized by nucleophilic substitution reactions of 4,4′‐difluorobenzophenone with 4,4′‐biphenyldiol and chlorohydroquinone. As expected, the copolymers have lower melting transitions than the biphenyldiol‐based homopoly(aryl ether ketone) because of the copolymerization effect of the crystal‐disrupting monomer chlorohydroquinone. Copolymers containing 50 and 70% biphenyldiol show two first‐order transitions which are associated with the crystal‐to‐liquid crystal transition and the liquid crystal‐to‐isotropic transition.
[η3‐methallyl‐nickel‐dad]PF6 complex: new catalyst precursor for ethylene polymerization
Authors: De Souza Roberto‐F. , Mauler Raquel S. , Simon Leonardo C. , Nunes Fernanda F. , Vescia Daniela V. S. , Cavagnolli Alessandro 
Published: April 2003

AbstractThe complex [η3‐methallyl‐nickel‐dad]PF6 is a new catalyst precursor for ethylene polymerization. The system is active in the presence of usual organoaluminium compounds like diethylaluminium chloride, at low Al/Ni ratios and under mild reaction conditions (temperatures between −10°C and 25°C, ethylene partial pressure from 1 to 15 atm). The polymers show extensive methyl branching, whose content is controlled by reaction parameters like temperature and ethylene pressure.
Hyperbranched methacrylates by self‐condensing group transfer polymerization
Authors: Simon Peter F. W. , Radke Wolfgang , Müller Axel H. E. 
Published: April 2003

AbstractThe synthesis of hyperbranched methacrylates was achieved by self‐condensing group transfer polymerization of 2‐(2‐methyl‐1‐triethylsiloxy‐1‐propenyloxy)ethyl methacrylate (1). “Back‐biting” is shown to be the predominant side reaction. In spite of this, the compact nature of the hyperbranched molecules was demonstrated through SEC‐viscosity measurements and comparison with a linear analogue. The degree of branching can be controlled by copolymerization with conventional monomers, e.g. MMA, and the living polymers can be used as macroinitiators for star‐shaped polymers.
Transition metal catalyzed atom Transfer Radical Polymerization (ATRP): from heterogeneous to homogeneous catalysis using 1,10‐phenantroline and its derivatives as new copper(I) ligands
Authors: Destarac Mathias , Bessière Jean‐Marie , Boutevin Bernard 
Published: April 2003

AbstractAtom Transfer Radical Polymerization (ATRP) of styrene is investigated in both heterogeneous and homogeneous media using 1‐phenylethyl chloride (1‐PECl)/CuCl/1,10‐phenantroline and derivatives as initiating systems. Using a 1‐PECl/CuCl/4,7‐diphenyl‐1,10‐phenantroline system in 1,2‐dimethoxybenzene as a solvent at 130°C, homogeneous ATRP of styrene leads to polymers with polydispersities down to 1,1. These new systems are compared with previously described 4,4′‐disubstituted 2,2′‐bipyridine‐based systems in terms of kinetics and quality of control.
Controlled radical polymerization of 4‐vinylpyridine
Authors: Bohrisch Jörg , Wendler Ulrich , Jaeger Werner 
Published: April 2003

Abstract2,2,6,6‐Tetramethylpiperidine‐N‐oxyl (TEMPO)‐mediated free radical polymerization of 4‐vinylpyridine is found to proceed in a “controlled” manner. A linear increase of molecular weight along with an increase in conversion occurs at varying temperatures. Polymerization of styrene with a poly(4‐vinylpyridine) block as macromer results in block copolymers with narrow polydispersity. The polymers are characterized by different size exclusion chromatography methods and converted to cationic polyelectrolytes as well as to polysulfo‐ and polycarbobetaines.
Polymerization of ethylene with nickel α‐diimine catalysts
Authors: Pappalardo Daniela , Mazzeo Mina , Pellecchia Claudio 
Published: April 2003

AbstractSeveral nickel α‐diimine compounds of the general formula (ArNC(R)C(R)NAr)NiX2 (Ar = 2,6‐alkyl substituted Ph, R = H or CH3, X = Br or CH3) were tested in ethylene polymerization after activation with different co‐catalysts, such as methylaluminoxane, Al(C2H5)2Cl or other aluminium alkyls, and ionizing reagents like B(C6F5)3, [CPh3][B(C6F5)4] or HBF4. The performances of the different catalytic systems were compared with reference to polymer productivity and structure. The degree of branching of the obtained polyethylenes was shown to depend not only on the ligand environment at the Ni centre but also on the type of co‐catalyst.
Synthesis of a star‐shaped polymer via coordination of ester‐linked pyridyl‐terminated poly(oxyethylene) with ru(II)
Authors: Naka Kensuke , Kobayashi Akiko , Chujo Yoshiki 
Published: April 2003

AbstractThe star‐shaped polymer with trans‐tetrapyridyl complex of Ru(II) as a core was prepared by complexation of ester‐linked pyridyl‐terminated poly(oxyethylene) (M̄n = 2000) with a Ru5Cl122− cluster. The unimodal peak of the star‐shaped polymer in the gel‐permeation chromatogram was shifted to a higher molecular weight region than that of the starting prepolymer. The electron‐withdrawing ester substituent in para position of the pyridine ring shifted the metal‐to‐ligand charge transfer (MLCT) band into the visible region.
Influence of mixed aluminoxane systems on ethylenenorbornene copolymerization catalyzed by metallocene
Authors: Wang Qi , Weng Jianhua , Fan Zhiqiang , Feng Linxian 
Published: April 2003

AbstractThe norbornene/ethylene copolymerization was investigated using Me2SiCp2MCl2 (M = Zr, Ti)/EBAO and MAO as catalyst systems (EBAO: mixed ethyl‐isobutylaluminoxane, MAO: methylaluminoxane). The copolymers were characterized by DSC and 13C NMR. Copolymers with high content of norbornene and high Tg were obtained with the mixed EBAO. It is suggested that the copolymerization is greatly influenced by the state of the ion pair of the metallocene catalyst. The effect of aluminoxane on the composition and the microstructure of copolymer is discussed.
Network models and their dynamics: probes of topological structure
Authors: Blumen Alexander , Jurjiu Aurel , Koslowski Thorsten 
Published: April 2003

AbstractIn this work we focus on the mechanical relaxation of macromolecules. Based on linear response theory, this relaxation is in general related to the set of eigenmodes and eigenfunctions of the system. Of particular importance are situations which lead to scaling in the time and frequency domains. Thus the relaxation of star polymers, of dendrimers and of hyperbranched structures does not display scaling. On the other hand, one expects that the relaxation of fractals, as in fact that of linear chains, does scale. Here we numerically analyse the behavior of networks modelled through finite Sierpinski‐type lattices, for which we have previously established that in the Rouse picture the mechanical relaxation scales in frequency and in time. As we show here, in the Zimm model based on the preaveraged Oseen‐tensor, the picture changes drastically; taking the hydrodynamic interactions into account leads to relaxation forms which do not scale.
Dielectric relaxations in polymers containing dioxacyclohexane rings by thermostimulated depolarization currents
Authors: Díaz‐Calleja Ricardo , Jesús Sanchis Maria , Aravena Milton , Riande Evaristo , Guzmán Julio 
Published: April 2003

AbstractThe dielectric activity of poly{5‐[(methacryloxy)methyl]‐5‐ethyl‐1,3‐dioxacyclohexane} (PMAMED) and poly[(5‐methacryloxy)‐1,3‐dioxacyclohexane] (PMAD) in the glassy region and in the glass‐rubber transition is investigated by using global and partial thermostimulated discharge current (TSDC) techniques. The global TSDC curve for each polymer displays an ostensible β absorption in the glassy region followed in increasing order of temperature for a prominent α glass rubber relaxation. Partial depolarisation curves show in detail the regions of the glassy state in which more dielectric activity occurs. The TSDC curves for PMAMED are compared with those of its acrylate homologous, poly{5‐[(acryloxy)methyl]‐5‐ethyl‐1,3‐dioxacyclohexane} (PAMED), finding that the methyl group in the former polymer only hinders long range micro‐Brownian motions in the chains, thus shifting the glass‐rubber relaxation to higher temperatures, without affecting in a significant way molecular motions in the glassy region. Small changes in the neighbourhood of the 1,3‐dioxacyclohexane ring, such as suppression of a methylene group or replacement of the equatorial hydrogen in position 2 of the ring for a phenyl group, depresses the dielectric activity and shifts the β absorptions to lower temperatures. The interconversion between TSDC and a.c. dielectric results in the glassy region is discussed.