bluuebunny/crossref_metadata_2025_split huggingface dataset:
Substituent effect in anionic polymerization of β‐lactones initiated by alkali metal alkoxides
Authors: Kurcok Piotr , Matuszowicz Andrzej , Jedliński Zbigniew , Kricheldorf Hans R. , Dubois Philippe , Jérôme Robert 
Published: April 2003

AbstractThe influence of methyl substituent on the mechanism of the ring‐opening polymerization of β‐lactones initiated by alkali metal alkoxides is discussed. Attention has been paid to the effect of the substituent position in the monomer molecule on the ring‐opening mechanism, the 3,3‐dimethyl‐2‐oxetanone (pivalolactone), 4‐methyl‐2‐oxetanone (β‐butyrolactone) and 2‐oxetanone (β‐propiolactone) being chosen as model monomers. Moreover, it was found unexpectedly that in the case of pivalolactone polymerization, besides open‐chain polymers, cyclic oligomers are produced.
Mesophases involving highly ordered smectic phases in a polyether
Authors: Cheng Stephen Z. D. , Yoon Yeocheol , Zhang Anqiu , Savitski Edward P. , Park Jae‐Young , Percec Virgil , Chu Peihwei 
Published: April 2003

AbstractBased on our differential scanning calorimetry observations, a polyether 1 synthesized from 4′‐[2‐(4‐hydroxyphenyl)propyl]‐4‐biphenylol and 1,9‐dibromononane shows multiple transition behavior during cooling and heating. Furthermore, these transition temperatures do not exhibit significant supercooling dependence. Detailed analyses of the wide‐angle X‐ray diffraction powder and fiber patterns at different temperatures have indicated that highly ordered smectic F and G phases exist in this polyether and are differentiated from traditional crystalline phases.
Synthesis and optical properties of some novel arylene‐alkynylene polymers
Authors: Mangel Timo , Eberhardt Anke , Scherf Ullrich , Bunz Uwe H. F. , Müllen Klaus 
Published: April 2003

AbstractThe synthesis and the optical properties of the novel aryleneethynylenes (7, 8) and arylenebutadiynylenes (10, 11) using either a Heck‐type or a Hay‐type coupling are reported. The route reported here also makes meta‐linked arylene‐alkynylenes accessible. The number‐average degree of polymerization of the obtained polymers is between 13 and 60. Some of the materials show promising optical properties (photoluminescence).
Cyclization reaction of polyacrylonitrile and poly(styrene‐co‐acrylonitrile) studied by PVT measurements
Authors: Kressler Jörg , Rudolf Bernd , Shimomai Ken , Ougizawa Toshiaki , Inoue Takashi 
Published: April 2003

AbstractPressure, volume, temperature (PVT) measurements reveal that during the intramolecular cyclization reaction of poly(acrylonitrile) (PAN) and poly(styrene‐co‐acrylonitrile) (SAN) the volume decreases. This volume contraction becomes smaller with increasing styrene content in the random copolymers and should be related to the simultaneous decrease of longer acrylonitrile homo‐sequences. The onset temperature of the cyclization reaction is raised with higher styrene contents in the random copolymers. Thus, it can be excluded that the cyclization reaction has a major influence on the discoloration process of SAN samples having relatively small acrylonitrile contents (less than 50 mol‐%) during thermal annealing below 300°C.
α‐olefin oligomers with narrow molar mass distributions from zirconocene/methylaluminoxane catalysts — An examination of the structure‐reactivity relationship
Authors: Janiak Christoph , Lange Katharina C. H. , Marquardt Peter 
Published: April 2003

AbstractA series of tert‐butyl substituted zirconocene/methylaluminoxane catalysts illustrates the potential for the tailoring of olefin oligomers with extremely narrow molar mass distributions, which are explained on the basis of a chain‐length dependent propagation rate. Comparative oligomerization experiments provide a means to estimate the relative rates for chain propagation versus chain transfer as well as a correlation with the metallocene structure.
Synthesis of novel hydrophobically modified water soluble polymers by ring‐opening metathesis polymerization
Authors: McArdle Clare M. , Hamilton James G. , Law Edwina E. , Rooney John J. 
Published: April 2003

AbstractRing‐opening metathesis polymerization has been used to prepare a series of water soluble polymers based on the Diels‐Alder adducts of furan and cyclopentadiene. Hydrophobically modified forms of these polymers were obtained either by copolymerization with 5‐decylbicyclo[2.2.1]hept‐2‐ene, post‐polymerization modification of the acid forms of the polymers with 1‐decylamine or chain transfer to 1‐hexadecene. Polymers were characterized by NMR specroscopy and viscometry.
Polymerisation of methyl methacrylate with tert‐butyllithium and triisobutylaluminium in toluene: mechanism of initiation and termination by matrix‐assisted laser desorption ionisation time‐of‐flight mass spectrometry (MALDI TOF MS)
Authors: Hunt Kirsty H. , Crossman Martin C. , Haddleton David M. , Lloyd Paul M. , Derrick Peter J. 
Published: April 2003

AbstractThe polymerisation of methyl methacrylate (MMA) using triisobutylaluminium/tert‐butyllithium in hydrocarbon at 0°C and −78°C has been investigated by matrixassisted laser desorption ionisation time‐of‐flight mass spectrometry (MALDI TOF MS). Although the system gives extremely good control over molecular weight and narrow molecular weight distribution, initiation of polymerization can be complicated by formation of small amounts of tert‐butyl isoprenyl ketone (1), and termination of polymerization can occur by end cyclisation of the end unit of 3. Both complications in initiation and termination can be avoided by suitable reaction conditions. Incorporation of 1 is suppressed by increasing the alkylaluminium content and by higher temperature. Termination by cyclisation has been found to occur over much longer time scales than propagation and can therefore be avoided by controlled termination after the appropriate reaction time.
Synthesis of a new microphase‐separated polymer system by “counterion coupling” and its X‐ray characterization
Authors: Antonietti Markus , Maskos Michael 
Published: April 2003

AbstractA new type of highly ordered, microphase‐separated polymer material is synthesized by simple ionic coupling of a commercial styrene/ethylene oxide twoblock copolymer with a charged end group to an oppositely charged polyelectrolyte by common precipitation from aqueous solution. The characterization of the polymer/polymer complex by small‐angle X‐ray scattering and polarization microscopy reveals that the comb‐like addition complexes formed by ionic grafting build up a mesophase with lamellar morphology and a periodicity of d = 7.1 nm which is easily oriented in mechanic fields.
ESCA surface study of polystyrene photodegradation accelerated by 2‐(2‐methoxy‐5‐methylphenyl)‐2H‐benzotriazole
Authors: Bottino Francesco A. , Di Pasquale Giovanna , Pollicino Antonino , Short Robert D. 
Published: April 2003

AbstractThe accelerated ageing of polystyrene by means of 2‐(2‐methoxy‐5‐methylphenyl)‐2H‐benzotriazole, under conditions reproducing the outdoor environment, was studied. The results show that this benzotriazole derivative appreciably accelerates the rate of photodegradation at the surface of polystyrene.
Fluorospectroscopy monitoring aggregation of block ionomers in aqueous media
Authors: Li Mei , Liu Lu , Jiang Ming 
Published: April 2003

AbstractA new type of aggregation behavior of block ionomers, i.e. functionalized polystyrene‐block‐poly[ethylene‐co‐(1‐butene)]‐block‐polystyrene (SEBS) with respective contents of 3.2 mol‐% and 8.3 mol‐% sodium carboxylate groups in polystyrene blocks has been studied using steady‐state fluorescence techniques. It is found that the block ionomers could form a stable dispersion in water although both the slightly ionized polystyrene block and the ethylene/1‐butene block are hydrophobic. The intensity ratio of the first to third vibronic band (I1/I3) of pyrene varies from 1.8, characteristic of the aqueous medium, to about 0.8, characteristic of hydrophobic microenvironment when the ionomer concentration in water is increased from 8 × 10−4 g/L to 2 × 10−1 g/L. Meanwhile, the emission intensity ratio of excimer to monomer (Ie/Im) of pyrene increases with increasing polymer concentration first, then passes through a maximum and eventually falls off to zero. Both of the methods show the same critical aggregation concentration (8 × 10−4 g/L). Besides the non‐radiative energy transfer efficiency between naphthalene and anthracene shows a considerable increase when the concentration reaches 0.01 g/L. All of these three approaches lead to the fact that the block ionomers could form hydrophobic aggregates in water stabilized by the rare ionic groups.
Evaluation of propagation rate constants for the free radical polymerization of methacrylonitrile by pulsed laser photolysis
Authors: Shipp Devon A. , Smith Trevor A. , Solomon David H. , Moad Graeme 
Published: April 2003

AbstractPropagation rate constants for the free radical polymerization of methacrylonitrile (MAN) have been obtained by pulsed laser photolysis (PLP). The temperature dependence of the propagation rate constants indicates a frequency factor of 10(6,43 ± 0,26) L · mol−1 · s−1 and an activation energy of 29,7 ± 1,5 kJ · mol−1. These parameters suggest that the relatively slow rate of propagation in MAN polymerization in relation to other common monomers (methyl methacrylate, styrene) can be attributed to the relative steric bulk and stability of the propagation species.
Photoinitiated thermolysis of poly(phenylenevinylene) precursor and photochemical doping of poly(phenylenevinylene)
Authors: Cho Iwhan , Kim Jinbaek , Lee Sungho 
Published: April 2003

AbstractThe photoinitiated elimination of methoxy groups of poly(p‐phenylene‐1‐methoxyethylene) and the photochemical doping of the resulting poly(phenylenevinylene) (PPV) were investigated. Upon irradiation and then heat treatment at 150°C, poly(p‐phenylene‐1‐methoxyethylene) containing triphenylsulfonium hexafluoroantimonate was converted to PPV. The resulting PPV was observed to be conductive, and its conductivity was 10−2–10−3 S/cm. By a lithographic procedure, we produced a conducting pattern doped photochemically in a nonconjugated poly(p‐phenylene‐1‐methoxyethylene) matrix.
Liquid‐crystalline epoxies dispersed liquid crystals
Authors: Lin Cui‐Lian , Chien Liang‐Chy 
Published: April 2003

AbstractDispersing liquid crystal droplets in a rigid polymer matrix results in an electrically controllable light scattering medium. A polymer with high glass transition temperature phase‐separated with a low molecular weight liquid‐crystalline material is a good binder for polymer dispersed liquid crystals (PDLC). Main‐chain liquid‐crystalline epoxies were synthesized for the phase separation with low molecular weight nematic liquid crystals E7 (mixture of 4‐alkyl‐4′‐cyanobiphenyls) and studied for their mesomorphic properties and response to an applied electrical field.
Structural characterization of syndiotactic 1,2‐poly(4‐methyl‐1,3‐pentadiene)
Authors: Meille Stefano V. , Capelli Silvia , Ricci Giovanni 
Published: April 2003

Abstract4‐Methyl‐1,3‐pentadiene was polymerized with the MAO/CpTiCl3 (MAO: methyl‐aluminoxane, Cp: Cyclopentadienyl) system to yield a highly stereoregular syndiotactic 1,2‐polymer. Fiber diffraction patterns indicate two crystalline modifications: a major one with a repeat of 11.73 Å and minor amounts of a zig‐zag planar polymorph (axial repeat 5.05 Å). Energy calculations account for three nearly isoenergetic conformations: the more stable one, with repeat of 11.65Å, is (T6G2T2G2) analogous to the one recently reported for syndiotactic poly(propylene) (Chatani et al., 1991).
Olefin polymerization with metallocene catalysts supported on polysiloxane derivatives
Authors: Soga Kazuo , Arai Takashi , Hoang Ban The , Uozumi Toshiya 
Published: April 2003

AbstractThree kinds of zirconocene catalysts, supported on polysiloxanes substituted with methylindenyl, methyl‐fluorenyl and two indenyl groups, respectively, were prepared and applied to propene and ethylene polymerizations using methylaluminoxane as cocatalyst. Both the activity and stereospecificity of these catalysts were found to lie between those of corresponding homogeneous and SiO2‐supported catalysts. Surprisingly, all the catalysts gave a mixture of atactic and isotactic poly(propylene), plausible reasons for which are briefly discussed.
Facilitated oxygen transport in an ionomer membrane containing cobaltous ions
Authors: Zhang Ziyong , Lin Shangan 
Published: April 2003

AbstractA new oxygen/nitrogen separation membrane based on an ionomer of sulfonated EPDM (ethylene‐propene‐diene terpolymer) containing Co2+ ions was synthesized and investigated. It was found that the oxygen permeability coefficient and the separation factor for O2/N2 of the ionomer membrane are simultaneously enhanced at lower gas pressure difference. This result is believed to be caused by a polymer coordinate complex formed in the ionomer. ESR spectra provided an evidence of the cobalt‐oxygen adduct.
Ethene polymerization with modified‐polypropene‐supported highly stable Ziegler catalyst
Authors: Mori Hideharu , Ohnishi Kouki , Terano Minoru 
Published: April 2003

AbstractA modified‐polypropene‐supported Ziegler catalyst was prepared using polypropene containing a small amount of poly(7‐methyl‐1,6‐octadiene) as a starting polymer for bromination, lithiation, and reaction with TiCl4. The polymerization of ethene was carried out using the catalyst with Al(C2H5)3 in toluene at 60°C up to 100 h. The polymer yield increased linearly with polymerization time, which indicates that the active sites of the modified‐polypropene‐supported Ziegler catalyst are practically stable without deactivation even for 100 h and are able to propagate further polymerization of ethene.
Styrene‐butadiene copolymerization initiated by organopotassium compounds in hydrocarbon medium
Authors: Nakhmanovich Boris I. , Arest‐Yakubovich Alexander A. , Prudskova Tatyana N. , Litvinenko Galina I. 
Published: April 2003

AbstractThe following values of monomer reactivity ratios were found: rS = 3,3 ± 0,3; rB = 0,12 ± 0,02 (cyclohexane, 25 °C). The comparison of the kinetic parameters obtained with Li, Na and K counter‐ions shows that the great difference between coordination polymerization with Li and “typically anionic” polymerization with K is mainly determined by the variation of the cross‐propagation rate constant kBS with the nature of the counter‐ion. No evidences for the specific role of the solvation of Li counter‐ion with butadiene monomer were found.
Synthesis of monodisperse hydroxyl‐containing polystyrene via chemical modification
Authors: Zhu Lei , Liu Lu , Jiang Ming 
Published: April 2003

AbstractA facile synthesis of linear monodisperse hydroxyl‐containing polystyrene, poly{styrene‐co‐[p‐(1‐hydroxyethyl)styrene]} and poly{styrene‐co‐[p‐(2‐hydroxypropan‐2‐yl)styrene]}, was carried out via chemical modification of polystyrene by a two‐step procedure, i. e. monodisperse polystyrene was acetylated under mild conditions, followed by processes of reduction with LiAlH4 and addition with CH3MgBr, respectively. 1H NMR and FTIR spectra showed that in both cases, the reaction of acetyl to hydroxyl is complete. Sizeexclusion chromatography demonstrated that both molecular weight and monodispersity of the final products were basically unchanged.
New optical properties of polyelectrolyte hydrogels
Authors: Budtova Tatiana , Vilesov Alexander , Bertsev Vladimir , Elikina Galina , Suleimenov Ibragim , Tolmachev Yurii 
Published: April 2003

AbstractA new optically active medium for lasers — a polyelectrolyte hydrogen swollen in a mixture of water + alcohol + dye — is presented. An anomalous dependence of the absorbance on the composition of the mixture is observed. It shows a maximum which corresponds to the composition when the hydrogel starts to swell as a hydrophilic network.
Preparation and properties of macromolecular complexes consisting of chitosan derivatives, iron(III) hydroxide sulfate, and poly(potassium vinyl sulfate)
Authors: Kikuchi Yasuo , Kubota Naoji , Fukuma Hirofumi , Mitsuishi Hiroshi 
Published: April 2003

AbstractGlycol chitosan (GC) and methyl glycol chitosan (MGC) were separately reacted with poly(potassium vinyl sulfate) (PVSK) in the presence of iron(III) hydroxide sulfate (IHS) to form water‐insoluble macromolecular complexes (MC's). The chemical compositions and properties of MC's obtained were compared with each other. The solubility of MC in the MGC‐IHS‐PVSK system was lower than that in the GC‐IHS‐PVSK system, and it was suggested that MGC contributes to the properties of MC.
Living diradical polymerization
Authors: Hammouch Saïd Oulad , Catala Jean‐Marie 
Published: April 2003

AbstractA diradical initiator containing two thermoreversible bonds was prepared and used for the polymerization of styrene at 90°C. The monomer consumption and the variation of the molecular weight were monitored with time. The results show that the process can be considered as living and that the polymerization rate is independent of the radical initiator concentration. By elemental analysis of the chain ends it was concluded that the propagation reaction occurs at both ends.
Topologically unique side‐chain polyrotaxanes based on triacetyl‐β‐cyclodextrin and a poly(ether sulfone) main chain
Authors: Born Markus , Ritter Helmut 
Published: April 2003

AbstractThe synthesis and NMR‐spectroscopical characterization of the topological arrangements of new side‐chain polyrotaxanes (3a) bearing about 80% of peracetylated cyclodextrins in the side‐chains of a functionalized poly(ether sulfone) is described. The characterizations have been conducted in relation to a similar model compound bearing no cyclodextrins (3b). The results strongly indicate that the cyclodextrins are uniformly located on the side chains, with the bigger opening over the aromatic anilide components of the barrier group. The glass transition temperature (Tg) of the polyrotaxane 3a is in the region of 143°C, which is significantly higher than that of the model polymer 3b having a value of 111°C.
Novel photocrosslinking of polymers bearing pendant acyloxyimino groups in the presence of p‐benzoquinone
Authors: Ito Ken‐ichi , Shigeru Yoshitaka , Tsunooka Masahiro 
Published: April 2003

AbstractFilms of polymers bearing pendant acyloxyimino (AOI) groups become insoluble when irradiated by ultraviolet light in the presence of p‐benzoquinone. Post‐heating of these films after irradiation also induces further the insolubilization. In the photocrosslinking, it is deduced that p‐benzoquinone serves not only as sensitizer for the decomposition of AOI groups but also as crosslinker during the photo‐irradiation and heating after irradiation.
Synthesis, optical absorption and fluorescence of new poly(p‐phenylene)‐related polymers
Authors: Remmers Marcus , Schulze Margit , Wegner Gerhard 
Published: April 2003

AbstractThe synthesis and properties of soluble, conjugated polymers consisting of oligo(p‐phenylene) sequences linked by ethylene, vinylene, or ethylene, units are reported. Benzene‐, stilbene‐, diphenylacetylene‐ and 1,2‐diphenylethane derivatives serve as monomers and are connected by the Suzuki‐coupling method. A wide range of poly‐(p‐phenylene)‐related polymers are available by the combination of different AA/BB‐type monomers in various concentrations. The optical properties of the resulting polymers can therefore be tailored. Number‐average degrees of polymerization of up to X̄n = 137 were reached under optimized conditions. Photoluminescence quantum yields of these materials in solution are nearly one.
Vanadium‐based Ziegler‐Natta catalyst supported on MgCl2(THF)2 for ethylene polymerization
Authors: Czaja Krystyna , Białek Marzena 
Published: April 2003

AbstractA supported magnesium‐vanadium‐aluminium catalyst was prepared by depositing –with the use of a milling technique–VOCl3 on the MgCl2(THF)2 support and subsequent activation with diethylaluminium chloride. Catalytic activity of the obtained system for ethylene polymerization was evaluated as a function of Mg/V and Al/V ratios as well as catalyst ageing time and polymerization temperature. High concentrations of THF in the catalytic system and considerable excess of an organoaluminium co‐catalyst were found to have no deactivating action on vanadium active sites. The catalyst obtained is stable and its activity for ethylene polymerization is high. It yields polyethylene with higher molecular weight and higher melting point than offered by the materials produced with the use of a corresponding unsupported vanadium catalyst or a titanium‐based system on the same magnesium support. Kinetic investigations confirmed stability of this catalyst irrespective of its concentration in the polymerization medium or of monomer concentration. Moreover, analysis of the kinetic findings revealed that over 80% of vanadium employed forms active polymerization sites.
Synthesis of poly(ethylene glycol) block copolymers by a redox process and their spectral characterization
Authors: Nagarajan Soundappan , Srinivasan Kalathur Sabdham Vangepuram 
Published: April 2003

AbstractNovel block copolymers of poly(ethylene glycol) (PEG) with acrylamide (AAm) and methacrylic acid (MAA) were synthesized using a redox system consisting of ceric ions and PEG in aqueous acidic medium. The molecular weight of PEG in the redox system was varied to obtain a series of block copolymers with differing molecular weights of PEG segment. The polymerization proceeded via macroradical generation, which was substantiated by ESR spectroscopy. This macroradical acted as a redox macroinitiator for the block copolymerization of the vinyl monomers. The formation of the block copolymers was confirmed by fractional precipitation technique.
Aggregate of a peptide‐containing block copolymer with a lipase
Authors: Naka Kensuke , Yamashita Rie , Nakamura Tohru , Ohki Akira , Maeda Shigeru , Aoi Keigo , Tsutsumiuchi Kaname , Okada Masahiko 
Published: April 2003

AbstractThe peptide‐containing block copolymer poly(N‐acetyliminoethylene)‐block‐poly(L‐phenylalanine) (1) formed large water‐soluble aggregates in water due to the hydrophobic and hydrogen‐bonding character of the poly(L‐phenylalanine) block. The solution properties of 1 were compared with those of the block copolymer poly(N‐acetyliminoethylene)‐block‐poly(N‐benzoyliminoethylene) (2) with an analogous structure. 1 formed aggregates even though the poly(phenylalanine) segment was short as compared with 2 in which hydrophobic interaction may be the only driving force to form aggregates. The aggregates have strong capability of incorporating Lipase P and largely increase the hydrolysis activity against p‐nitrophenyl propionate as compared with that of free Lipase P.
Solid‐like states of a dendrimer liquid displayed by scanning force microscopy
Authors: Sheiko Sergei S. , Eckert Gabi , Ignat'eva Galina , Muzafarov Aziz M. , Spickermann Jochen , Räder Hans J. , Möller Martin 
Published: April 2003

AbstractAdsorption and aggregation of carbosiloxane dendrimers on mica and pyrolytic graphite were investigated by scanning force microscopy (SFM). The aggregation process started from (i) single molecules which coagulated to (ii) clusters and (iii) fluid droplets followed by formation of (iv) a complete layer on the solid substrate. The molecules were displayed as a globular particle with a diameter of about 2.5 nm. Tapping SFM of the liquid was possible due to the fact that the dendrimer undergoes a transition to a viscoelastic state below the tapping frequency of about 360 kHz. Dynamic shear compliance experiments have shown a plateau of 5 · 10−7 Pa−1 around this frequency. Dendrimer droplets slowly spread into polygonal lamellae with a thickness of two molecular layers. The structures indicate a rather regular dense packing of the globular molecules.