bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comments on the paper “Living cationic polymerization of styrene monomers” by M.‐L. Yang, K. Li and H. D. H. Stöver
Authors: Matyjaszewski Krzysztof 
Published: April 2003

AbstractThe mechanism of cationic polymerization of styrene monomers leading to well defined polymers proposed by Yang, Li and Stöver is criticized. The growth does not occur on the “colorless nondissociated ion pair” represented as polarized covalent species but includes dynamic equilibration between covalent species and carbocations. In addition, ligand exchange between 1‐phenylethyl bromide and SnCl4 leads to the formation of Lewis acids with much more labile Sn‐halide bonds. The observed colors are due to the generation of side products, presumable indanyl cations, and not to the alleged propagating free ions.
Synthesis of polypropene‐block‐poly(ethylene‐co‐propene) by short‐period polymerization with MgCl2‐supported Ziegler catalyst
Authors: Mori Hideharu , Yamahiro Mikio , Tashino Kunihiko , Ohnishi Kouki , Nitta Koh‐hei , Terano Minoru 
Published: April 2003

AbstractThe short‐period polymerization method was successfully applied to the synthesis of a novel diblock copolymer, polypropene‐block‐poly(ethylene‐co‐propene). The polymerization was carried out for ca. 0,1 s with a MgCl2‐supported Ziegler catalyst. The copolymers obtained showed unimodal curves in gel‐permeation chromatography without any peak in the low‐molecular‐weight region. After extraction with heptane, the fraction of poly(ethylene‐co‐propene) remained unchanged in the copolymer but disappeared in a commercial so‐called block‐type copolymer. All the results the formation of polypropene‐block‐poly(ethylene‐co‐propene), in which poly(ethylene‐co‐propene) is chemically linked with polypropene.
Synthesis of a biodegradable polymeric supramolecular assembly for drug delivery
Authors: Ooya Tooru , Mori Hideharu , Terano Minoru , Yui Nobuhiko 
Published: April 2003

AbstractA novel design of a biodegradable carrier for drug delivery was established by constructing a supramolecular assembly of drugs and polymer backbones without any covalent bonds. A biodegradable polyrotaxane was synthesized in which α‐cyclodextrins (α‐CDs) as drug carriers were threaded onto poly(ethylene glycol) chains which then were capped at each chain end by L‐phenylalanine via peptide linkages. The release of α‐CDs was observed only when the terminal peptide linkages were degraded.
Regiospecificity of 1‐butene polymerization catalyzed by C2‐symmetric group IV metallocenes
Authors: Busico Vincenzo , Cipullo Roberta , Borriello Anna 
Published: April 2003

AbstractThe regiospecificity of isotactic 1‐butene polymerization promoted by typical C2‐symmetric group IV metallocene catalysts was studied by means of 13C NMR spectroscopy. In particular, the formation of 1,4 monomer enchainments is discussed.
Synthesis of metal‐complexing latices via polymerization in microemulsion
Authors: Antonietti Markus , Lohmann Sabine , Eisenbach Claus D. , Schubert Ulrich S. 
Published: April 2003

AbstractMicrolatex dispersions with ca. 120 m2 bipyridine‐functionalized surface per g polymer were synthesized via copolymerization in microemulsion using two new comonomers containing bipyridine groups. The resulting polymer particles were used for binding diverse metal ions in water as well as in organic solvents. Binding of the ions usually occurs intramolecularly. The colloidal characteristics of the dispersions are preserved.
Ethylene polymerization initiated by SiO2‐supported neodymocene catalysts
Authors: Jin Jizhu , Uozumi Toshiya , Soga Kazuo 
Published: April 2003

AbstractSome SiO2‐supported neodymocene catalysts were prepared and polymerization of ethylene was conducted with them using alkylaluminiums, methylaluminoxane (MAO), BuLi and Bu MgEt (Bu: butyl, Et: ethyl) as cocatalysts. The lifetime of these catalysts was found to be very long. Catalytic activity as well as molecular weight of the produced polymer are strongly dependent upon kind and amount of cocatalyst used. With increasing polymerization temperature, the activity increases monotonously up to 80°C. The use of BuMgEt and Al(i‐C4H9)3 as cocatalyst gives the highest activity and highest molecular weight, respectively.
UV‐initiated solidification of liquid crystalline ethylcellulose/acrylic acid films and bands formed in this process
Authors: Zhao Chun‐tian , Cai Bao‐lian 
Published: April 2003

AbstractSolidification of liquid crystalline ethylcellulose/acrylic acid films was realized by UV‐initiated polymerization of the solvent acrylic acid. It has been found that the original textures were immobilized to a great extent, and a novel “banded texture” formed at the same time. The optical properties of this texture were different from the banded texture formed by shearing lyotropic or thermotropic polymer liquid crystals. Formation of such bands is assumed to be related to an uncompleted phase separation.
Isotactic cis‐1,4‐poly(3‐methyl‐1,3‐pentadiene): a new conformation for isotactic cis‐1,4‐polydienes
Authors: Meille Stefano Valdo , Capelli Silvia , Allegra Giuseppe , Ricci Giovanni 
Published: April 2003

AbstractOriented specimens of isotactic cis‐1,4‐poly(3‐methyl‐1,3‐pentadiene) exhibit two crystalline modifications characterized, respectively, by the expected two‐fold helical conformation with a fiber repeat of 8,02 Å and by a three‐fold helix with c = 9,97 Å. The latter highly contracted structure is prevalent in fibers and is the only one observed in unoriented bulk specimens. Consistent with these findings conformational calculations indicate that the three‐fold helix is substantially more stable than the two‐fold one.
Synthesis and characterization of a chlorofunctionalized unsaturated carbosilane oligomer
Authors: Cummings Sophia K. , Smith Dennis W. , Wagener Kenneth B. 
Published: April 2003

AbstractAcyclic diene metathesis (ADMET) polymerization offers a viable route for the synthesis of chlorofunctionalized unsaturated carbosilane oligomers. The SiCl bond in unsaturated carbosilane monomers remains inert during metathesis and the use of a highly reactive molybdenum‐based, Lewis acid‐free alkylidene catalyst affords unsaturated chlorofunctionalized carbosilane oligomers with known vinyl end groups. The first synthesis of an unsaturated carbosilane oligomer functionalized with a SiCl bond was performed. A chlorofunctionalized silacyclopentene product was also observed, due to a backbiting reaction. This new class of functionalized oligomers has a low glass transition temperature and sites of unsaturation which may be used for further reaction. ADMET chemistry now provides access to a variety of chlorofunctionalized unsaturated carbosilanes which can be used to tailor make hydrolytically stable carbosilane oligomers and polymers via nucleophilic grafting reactions.
The influence of the transition metal and the heteroatomic‐bridge on the action of metallocene/methyl aluminoxane catalysts in ethylene polymerization and on the properties of the polymer
Authors: Quijada Raul , Dupont Jairton , Silveira Dione Corrêa , Miranda Márcia S. Lacerda , Scipioni Rosângela B. 
Published: April 2003

AbstractThis work reports a comparative study of the catalytic behaviour for a series of metallocenes derived from Ti, Zr, Hf and Nb, which after activation with methylaluminoxane can polymerize ethylene. Results show that the Zr metallocene with a (CH3)2SiBridge presents the highest activity, and the metallocenes based on Hf and Nb do not show any significant activity under the tested conditions.
Synthesis and mesomorphic behavior of poly(dipropylsilylenemethylene)
Authors: Koopmann Florian , Frey Holger 
Published: April 2003

AbstractBased on the reaction of trichloro(chloromethyl)silane (1) with 2 equivalent amounts of the respective Grignard‐reagent and subsequent cyclization, 1,1,3,3‐tetrapropyldisilacyclobutane (3) has been prepared. Catalytic polymerization with H2PtCl6 was employed to prepare the corresponding poly(dipropylsilylenemethylene) (PDPSM, 4) with strictly alternating SiR2/CH2 backbone structure. A high‐molecular‐weight fraction of the material (weight‐average molecular weight M̄w = 166 500 and number‐average molecular weight M̄n = 115 200) obtained by fractionating precipitation was investigated with respect to glass transition and formation of conformationally disordered mesomorphic phases. The glass transition temperature Tg = 232 K of PDPSM evidenced lower backbone flexibility than observed for the analogous poly(dipropylsiloxane), (PDPS). PDPSM exhibited mesomorphic behavior. In contrast to poly(dipropylsiloxane), PDPSM showed a surprisingly narrow mesomorphic regime between 355 K and 365 K. Based on polarizing microscopy and 29Si‐MAS (magic angle spinning) solid‐state NMR the mesophase is described as a conformationally disordered state, which is most probably columnar in analogy to PDPS.
Characterization of polybutadiene produced with CoBr2(PPh3)2‐based catalysts
Authors: Takeuchi Masaki , Shiono Takeshi , Soga Kazuo 
Published: April 2003

AbstractPolymerization of 1,3‐butadiene was conducted with the CoBr2(PPh3)2(Ph: phenyl)‐methylaluminoxane (MAO) and MgCl2‐supported CoBr2(PPh3)2‐Al(CH3)3 catalyst systems. The microstructure of polybutadiene was analyzed in detail by 13C NMR spectroscopy after hydrogenation, which indicated that the distribution of the 1,2 and 1,4 units in polybutadiene is more random when the homogeneous CoBr2(PPh3)2‐MAO catalyst was used. The microstructure of these polymers was compared with that obtained using BuLi as catalyst.
Bifunctional polytetrahydrofuran initiator for sequential photochemical and thermal initiation
Authors: Denizligil Selcuk , Baskan Aysegul , Yagci Yusuf 
Published: April 2003

AbstractThe polymerization of tetrahydrofuran was initiated with 4,4′‐azobis(4‐cyanovaleryl chloride) in conjunction with silver hexafluoroantimonate and the living polytetrahydrofuran (PTHF) was terminated with pyridinium N‐oxide derivatives. The resulting PTHF‐macroinitiator possesses both a thermally and photochemically labile group.
Polymerizable mesoions, 2. Radical polymerization and 1,4‐dipolar polycycloaddition of a 4‐vinylphenyl‐modified mesoionic 4,6‐dioxo‐1,3‐diazine
Authors: Ritter Helmut , Sperber Rolf 
Published: April 2003

AbstractMesoionic 5‐methyl‐4,6‐dioxo‐3‐phenyl‐1‐(4‐vinylphenyl)‐1,3‐diazine (5) was obtained by condensation of 3‐phenyl‐1‐(4‐vinylphenyl)formamidine (3) with methylmalonic acid (4). This vinyl‐substituted mesoionic heterocyclic compound was polymerized by usual radical initiation and, additionally, by thermally controlled polycycloaddition in solution, yielding two different types of polymers, 6, 7. According to the X‐ray diffraction analysis, the structure of a low molecular weight model proves the regioselectivity of the polycycloaddition.
Synthesis of poly(tert‐butoxycarbonyl‐p‐phenylene): precursor to poly(p‐phenylene)
Authors: Ueda Mitsuru , Yoneda Masanobu 
Published: April 2003

AbstractPoly[2‐(tert‐butoxycarbonyl)‐1,4‐phenylene] (2) was prepared by the Ni‐catalyzed polymerization of tert‐butyl 2,5‐dichlorobenzoate (1). The microstructure of polymer 2 was probably alternating head‐to‐head and tail‐to‐tail. This polymer was soluble in dipolar aprotic solvents, chloroform, tetrahydrofuran, and dichloromethane. Polymer 2 was saponified easily by thermal or acid treatment to yield poly[2‐carboxy‐1,4‐phenylene] (3). Decarboxylation of polymer 3 in quinoline in the presence of copper(II) oxide produced poly(p‐phenylene) (PPP) (4).
Kinetic study of free‐radical copolymerization of ethyl α‐benzoyloxymethylacrylate with methyl methacrylate in benzene
Authors: Cuervo‐Rodríguez Rocío , Fernández‐Monreal M Carmen , Fernández‐García Marta , Madruga Enrique L. 
Published: April 2003

AbstractFrom a phenomenological point of view, the Mayo‐Lewis terminal model can describe both copolymer composition and the variation of copolymerization rate for the ethyl α‐benzoyloxymethylacrylate/methyl methacrylate/benzene/2,2′‐azoisobutyronitrile system.
Synthesis of hydroxy‐terminated poly(vinyl ethers) by living cationic polymerization, 2. Poly(2‐chloroethyl vinyl ether): a telechelic polymer with reactive pendants
Authors: Hashimoto Tamotsu , Aizawa Hideaki , Kodaira Toshiyuki 
Published: April 2003

AbstractHydroxy‐terminated telechelic poly(2‐chloroethyl vinyl ether) (poly(CEVE)) was synthesized by water‐based end‐capping reaction of living poly(CEVE) with the initiating system CH3CHClOCH2CH2OCOCH3/ZnCl2 in CH2Cl2 at −40°C and subsequent end‐group transformation of the acetate (α‐end) and aldehyde (ω‐end) groups into hydroxy groups. The obtained polymers possess controlled molecular weights and narrow molecular weight distributions.
Block copolymer with liquid‐crystalline polyacrylate and poly(propylene oxide) segments
Authors: Gomes Aílton S. , Carvalho Kalen S. , Pinto Maurício R. 
Published: April 2003

AbstractA new route of synthesis of block copolymers was investigated. It involves the polymerization of a side‐chain liquid‐crystalline acrylate and poly(propylene glycol), modified by an esterification reaction with mercaptoacetic acid used as macrotransfer agent, in the presence of 2,2′‐azoisobutyronitrile as initiator. The molecular weight of the liquid‐crystalline blocks is determined by the molar ratio between the reactants.
Polypyridine block as molecular antenna in photoluminescence of macromolecular systems
Authors: Yamamoto Takakazu , Yoneda Yutaka , Kizu Kenichi 
Published: April 2003

AbstractUnique effects of π‐conjugated polypyridine (PPy) blocks on fluorescence from the following macromolecular systems have been examined: (A) poly(2,2′‐bipyridine‐5,5′‐diyl) (PBpy)‐Ru(bpy)2, (b) block‐type copolymer of pyridine and selenophene, and (c) a system containing poly(6‐hexylpyridine‐2,5‐diyl) (6HexPy) and poly(2‐methylanthraquinone‐1,4‐diyl) (P2MeAQ). The PPy blocks in the systems serve as good molecular antennas and transfer the photoactivated energy to other molecular parts of the systems connected to the PPy blocks, thus causing emission of light from the other molecular parts.
Acyclic diene metathesis (ADMET) depolymerization: The synthesis of 1,4‐polybutadiene telechelics
Authors: Wagener Kenneth B. , Marmo J. Christopher 
Published: April 2003

AbstractADMET depolymerization is a viable route in the formation of tailored‐molecular‐weight polybutadiene telechelics. The bulk depolymerization requirement is met by initially forming macrocyclic butadiene, thereby decreasing the amount of macrocyclic formation. This synthetic scheme is capable of generating well‐defined, tailored‐molecular‐weight polybutadiene telechelics (M̄n = 2600).
Copolymerization of 1,3‐butadiene and styrene with a neodymium catalyst
Authors: Oehme Annekatrin , Gebauer Ulrich , Gehrke Klaus , Lechner M. Dieter 
Published: April 2003

AbstractHomo‐ and copolymerization of butadiene and styrene in the presence of the catalyst system Nd(octanoate)3/CCl4/Al(iBu)3 (iBu: isobutyl) were investigated at 60°C in heptane as solvent. The initiating catalyst system is very effective in the polymerization of butadiene. However, the presented copolymerization of butadiene and styrene is only practicable when using a special addition order of the catalyst components and a prescribed ageing phase. Copolymers obtained from various monomer feed ratios were characterized by 1H and 13C NMR spectroscopy and gel‐permeation chromatography (GPC). The copolymer characteristics especially microstructure, molar mass and molar‐mass distribution (MMD) are strongly dependent on the composition of the monomer mixture.
Highly oxygen permselective membrane prepared from cobalt‐complexed polyazomethine containing a ligand and a tri‐ or tetrasiloxane in the main chain
Authors: Shin Kyounghan , Aoki Toshiki , Oikawa Eizo 
Published: April 2003

AbstractTwo types of polyazomethines containing repetitive pairs of a tridentated ligand and an oligodimethylsiloxane in the backbone were synthesized and complexed with cobalt ion. The resulting polymer complex membranes showed very good oxygen permselectivity at 1 atm pressure difference, which is very close to the upper boundary line in an α vs. Po2 plot of data reported in the literature. The complexes are thought to function as oxygen carrier.
Formation of block copolymer micelles in solutions of a linear homopolymer in a good solvent
Authors: Quintana José R. , Jáñez María D. , Katime Issa 
Published: April 2003

AbstractThe existence of micelles of polystyrene‐block‐poly(ethylene/propene) in solutions of polystyrene in toluene was investigated. Toluene is a good solvent of both copolymer blocks whereas polystyrene and poly(ethylene/propene) are immiscible polymers. The presence of homopolystyrene at high enough concentration can induce the micellization of polystyrene‐block‐poly(ethylene/propene) in solution of a good solvent such as toluene. The thermodynamics of this new micelle system at a given polystyrene concentration was studied. Light scattering measurements were carried out in order to determine the critical micelle temperature (CMT) of different micellar solutions. Standard Gibbs energy, enthalpy and entropy of micellization were estimated from CMT and concentration data. The numerical values found were less negative than those found for micelle systems consisting in a block copolymer dissolved in a single selective solvent.
Enzyme‐catalyzed syntheses of poly(1,6‐hexanediyl maleate) and poly(1,6‐hexanediyl fumarate) in organic medium
Authors: Mezoul Gilles , Lalot Thierry , Brigodiot Maryvonne , Maréchal Ernest 
Published: April 2003

AbstractThe lipase‐catalyzed preparation of poly(1,6‐hexanediyl maleate) by transesterification of 1,6‐hexanediol and dimethyl maleate is described. A configurationally pure poly(1,6‐hexanediyl maleate) exhibiting exclusively cis structure was obtained. During the reaction, a substantial amount of macrolactones was formed. They were isolated, and the cyclic oligomer with y = 2 was found to predominate. Cycles are semi‐crystalline, while no melting point was detected for the linear poly(1,6‐hexanediyl maleate). We assume that the linear unsaturated polyester is completely amorphous owing to its cis configuration.
Structure formation of liquid‐crystalline isotropic AB block copolymers in nematic solvents
Authors: Walther Mathias , Bohnert Robert , Derow Stephan , Finkelmann Heino 
Published: April 2003

AbstractAB block copolymers with an isotropic and a nematic block are synthesized by living anionic copolymerization of isotropic and mesogenic methacrylates. The complete phase diagrams of the corresponding homopolymers with the nematic solvent have been established. In dilute solution (0.2 to 5% by weight) in a low‐molar‐mass nematic solvent, the copolymers exhibit two different types of structure formation. Polymers with high isotropic block fraction form irreversible networks as a results of phase separation followed by vitrification of the polymer‐rich phase. Polymers with high nematic block fraction on the other hand form thermoreversible threadlike structures perfectly ordered parallel to the director of the nematic solvent. These structures cannot be explained by a macroscopic phase separation process but more likely by a formation of micellar‐like aggregates.
Doublestimuli‐responsive degradable hydrogels for drug delivery: Interpenetrating polymer networks composed of oligopeptide‐terminated poly(ethylene glycol) and dextran
Authors: Kurisawa Motoichi , Terano Minoru , Yui Nobuhiko 
Published: April 2003

AbstractBiodegradable hydrogels composed of oligopeptide‐terminated poly(ethylene glycol) (PEG) and dextran with interpenetrating polymer network (IPN) structure were proposed as a novel substrate for multistimuli‐responsive drug delivery. IPN‐structured hydrogels were synthesized by sequential crosslinking reactions of N‐methacryloyl‐glycilglycilglycil‐terminated PEG and dextran. In vitro degradation of the IPN‐structured hydrogels was examined using papain and dextranase as model enzymes for hydrolyzing the oligopeptide and the dextran. Specific degradation in the presence of papain and dextranase was observed in the IPN‐structured hydrogel with a particular composition of PEG and dextran, whereas this hydrogel was not degraded by one of the two enzymes.
A polarographic study of propene‐maleic anhydride copolymers
Authors: Werner Kirsten , Steinert Volker , Reinhardt Steffi 
Published: April 2003

AbstractThe polarographic behaviour of hydrolyzed propene‐maleic anhydride copolymers in the interval pH 2.0–11.0 has been investigated by differential pulse polarography in aqueous lithium chloride solution at 25°C. In dependence on the pH‐value, one, two or three signals, belonging to the acid groups in the copolymer, appear in the polarograms. Three apparent polarographic acid constants have been determined graphically from the changes in the half‐wave potential of the separate peaks in correlation with pH.
Towards periodic copolymers with flexible and mesogenic units in the main chain. Copolymerization of tetrahydrofuran with 7‐oxabicyclo[2.2.1]heptane
Authors: Libiszowski Jan , Szymanski Ryszard , Penczek Stanislaw 
Published: April 2003

AbstractAn attempt was made to prepare periodic polymers having promesogenic units of various lengths. Due to a certain distribution within these units, copolymers of this structure should rather be called pseudoperiodic. In order to understand better the behaviour of such systems, copolymerization of tetrahydrofuran (THF — soft units) with 7‐oxabicyclo[2.2.1]‐heptane (BC — hard units) was studied. The kinetically and thermodynamically controllable copolymerizations were elaborated, leading to products of different distribution of the THF and BC units. The apparent reactivity ratios are dependent on the copolymerization conditions due to the reversibility of the propagations on the THF type of active species. They vary: r̄1 from 0.09 to 2.72, r̄2 from 0.31 to 1.57 (1 stands for BC, 2 for THF). Pseudoperiodic copolymers of the structure \documentclass{article}\pagestyle{empty}\begin{document}$\rlap{-} [\rlap{&#x02013;} ({\rm BC}\rlap{-} )_x {\rm THF}\rlap{-} ]_n $\end{document}, where x̄ = 1 to 4, were prepared carrying out the copolymerization above the ceiling temperature of THF.
One‐step synthesis of 2,6‐naphthalenedicarboxylic acid from naphthalene using cyclodextrin as catalyst
Authors: Hirai Hidefumi , Shiraishi Yukihide , Shirai Hiroaki 
Published: April 2003

AbstractThe one‐step synthesis of 2,6‐naphthalenedicarboxylic acid from naphthalene with carbon tetrachloride, copper powder and aqueous alkali has been achieved under mild conditions by the use of β‐cyclodextrin as catalyst, producing 2,6‐naphthalenedicarboxylic acid in 65 mol‐% yield with 79% selectivity.
Effect of tetraalkylammonium salts on the tacticity of poly(methyl methacrylate), 1. Initiation by ethyl α‐lithioisobutyrate
Authors: Novakov Christo P. , Tsvetanov Christo B. 
Published: April 2003

AbstractThe anionic polymerization of methyl methacrylate (MMA) was carried out in the presence of ethyl α‐lithioisobutyrate (α‐LiEtIB)/quaternary ammonium salts (QAS) in toluene and tetrahydrofuran/toluene (vol. ratio 75/25) at −60°C. It was found that the tacticity of PMMA strongly depends on size and shape of QAS. A highly isotactic polymerization in toluene was observed, when using the system α‐LiEtIB/trimethylhexadecylammonium bromide. The initiator system α‐LiEtIB/tetrahexylammonium chloride produces polymers with a high (>50%) syndiotactic content and relatively low polydispersity. The influence of QAS on the mode of polymerization is due to specific salt effect resulting from the cation exchange reaction, from the participation of the bulky substituent in the primary solvation shell, and ionic aggregation between the growing anion, Q+ and LiX.