bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reversible alignment change of liquid crystals induced by photochromic molecular films, 15. Convenient methods to prepare “command surfaces” by surface‐selective modification of thin films of poly(vinyl alcohol) with azobenzene units
Authors: Aoki Koso , Seki Takahiro , Sakuragi Masako , Ichimura Kunihiro 
Published: April 2003

AbstractA thin film of poly(vinyl alcohol) (PVA of different saponification degree) coated on a glass plate was subjected to a surface‐selective introduction of azobenzene moieties by treatment with a solution of 4‐(4‐hexylphenylazo) phenoxyacetyl chloride/pyridine or 4‐(4‐hexylphenylazo) phenoxybutanal /ptoluenesulfonic acid. Cells were fabricated by sandwiching a nematic liquid‐crystalline material between two surface‐modified glass plates. Alternating exposure to UV and visible light causes a reversible alignment of the liquid crystal molecules. Rubbing of the surface‐modified PVA resulted in an improved optical quality of the cell and enabled us to construct a photoresponsive twisted nematic cell. The advantages of the present method for preparing “command surfaces” are discussed from a practical point of view.
The influence of inert diluents on the structure and properties of lightly crosslinked acrylonitrile‐divinylbenzene copolymers
Authors: Wojaczyńska Maria , Kolarz Bozena N. , Hlavata Drahomira , Liesiene Jolanta , Gorbunov Aleksiej 
Published: April 2003

AbstractThe influence of solvents in the suspension polymerization of acrylonitrile and divinylbenzene on the structure of the resulting copolymers was tested. The solvents used were toluene or cyclohexanol in mixtures with aliphatic hydrocarbons. It was found that the solution conditions during the polymerization have no essential influence on both crystallinity and the structure of the dry copolymers. However, the properties of the copolymers differ markedly in the gel state. The copolymers obtained in the presence of good solvents show gel permeabilities and sorbabilities toward phenols several times higher than those of copolymers synthesized in the presence of poor solvents.
Synthesis and properties of aromatic polyamides derived from 2,7‐bis(4‐aminophenoxy)napthalene and aromatic dicarboxylic acids
Authors: Yang Chin‐Ping , Chen Wen‐Tung 
Published: April 2003

Abstract2,7‐Bis(4‐aminophenoxy)naphthalene, a new polymer‐forming diamine, was synthesized in two steps by the preparation of 2,7‐bis(4‐nitrophenoxy)naphthalene from 2,7‐dihydroxynaphthalene and p‐chloronitrobenzene and subsequent reduction with a 10% Pd‐C catalys and hydrazine hydrate. Aromatic polyamides and copolyamides having an inherent viscosity in the range of 0,76–1,16 dL/g were prepared by the direct polycondensation of the diamine with various aromatic dicarboxylic acids or with mixed dicarboxylic acids in 1‐methyl‐2‐pyrrolidone (NMP) using triphenyl phosphite and pyridine as condensing agents. Most of the polymers were soluble in aprotic solvents such as NMP and N,N‐dimethylacetamide (DMAc), and afforded transparent, flexible and tough films upon casting from DMAc solutions. Glass transition temperatures of the polymers were in the range of 246–327°C, and 10% weight loss temperatures were above 501°C in nitrogen and 476°C in air, respectively.
Synthesis of soluble p‐terphenyl‐4,4″‐ylene sulfide polymers
Authors: Kallitsis Joannis K. , Naarmann Herbert 
Published: April 2003

AbstractThe synthesis of substituted poly(p‐terphenyl‐4,4″‐ylene sulfide)s was carried out via nucleo‐philic displacement of the chlorine atom from 4,4″‐dichloro‐2′,3′‐disubstituted p‐terphenyls by sodium sulfide. Different aromatic groups such as phenyl, p‐methoxyphenyl, biphenylyl, phenoxyphenyl and phenylthiophenyl were used as substituents. Polymers containing sulfur near the theoretical values were obtained in most cases. The synthesized polymers are soluble in common solvents at room temperature when substituents bulkier than the phenyl group were used. Inherent viscosity values of up to 0,38 dL/g were achieved. Dynamic mechanical analysis showed that polymer films were obtained with a modulus independent of temperature up to 250°C. Thermal stability of the synthesized products was evaluated by thermogravimetry, showing that the polymers are stable up to 500°C in both air and nitrogen atmosphere. Products having a glass transition temperature in the range of 135 to 230°C, determined by differential scanning calorimetry, were obtained by this method.
Cationic polymerization of (Z)‐2‐ethoxyvinyl acetate
Authors: Wulff Günter , Birnbrich Paul 
Published: April 2003

AbstractThe new monomer (Z)‐2‐ethoxyvinyl acetate (5) was prepared diastereoselectively. It contains both an acetoxy and an ethoxy group on the same olefinic bond, and it was of interest to investigate its polymerization behaviour. In contrast to vinyl acetate, it can be polymerized by cationic initiation to form polymers of moderate molecular weight. The molecular weight distribution is surprisingly narrow (Mw/Mw ≈ 1,15 − 1,25)though this is not a living polymerization system. The polymerization is anticipated to proceed via a stabilized acetoxonium ion. In poly(1‐acetoxy‐2‐ethoxyethylene), (6), the acetyl group can be methanolyzed, yielding poly(1‐ethoxy‐2‐hydroxyethylene) (7), a polymer with high solubility in polar solvents.
Conductivity relaxation of neutral poly(3‐octylthiophene)
Authors: Chen Show‐An , Liao Chien‐Shiun 
Published: April 2003

AbstractDielectric relaxation (−90°C to 120°C, 0,4 Hz to 105 Hz) and ultraviolet‐visible (UV/Vis) spectroscopic (−100°C to 200°C) measurements for poly(3‐octylthiophene) were carried out. A correlation of complex electric moduli, which were converted from dielectric measurements, with thermal transitions from UV/Vis and dynamic mechanical analysis indicates (i) no significant effect of side‐chain motion on charge transport; (ii) in the glass transition and rubbery regions relaxation time distribution becomes broadened with temperature; (iii) as the coplanar subchains in the order region melt, the relaxation time distribution becomes more narrow.
Azide function and polyaddition: reaction of 2‐azido‐2,4,4‐trimethylpentane and monoazidopoly(2‐methylpropene) with some dienophiles
Authors: Nguyen Hung Anh , Cheradame Hervé , Maréchal Ernest 
Published: April 2003

AbstractThe 1,3‐dipolar addition of 2‐azido‐2,4,4‐trimethylpentane (1) to acetylene and ethylene derivatives such as phenylacetylene (2), acrylonitrile, diphenyl fumarate (4) and N,N′‐methylenebis(1,4‐phenylene)dimaleimide (8) leads to the corresponding triazole and triazoline derivatives. This study demonstrates that tertiary azides are able to react with dienophiles, and the application of this reaction for the synthesis of block copolymers was investigated with monoazido‐telechelic poly(2‐methylpropene) (PMP). It was shown that the azido group is stable under the severe conditions of the polycondensation reaction without decomposition (170°C, 24 h), and the monoadduct PMP‐8 is produced with acceptable yield.
Studies on polyamide 3 — synthesis, characterization and properties
Authors: Morgenstern Ute , Berger Werner 
Published: April 2003

AbstractThe synthesis of polyamide 3 (PA 3) by hydrogen transfer polymerization is described. The reaction proceeds homogeneously in N,N‐dimethylacetamide/LiCl in contrast to the heterogeneous reaction in 1,4‐dioxane and pyridine. By IR, NMR, differential scanning calorimetry and extraction experiments it was shown that the reaction product is nearly pure PA 3.
Polymers of carbonic acid, 8. Linear polybiurets
Authors: Kricheldorf Hans R. , Meier‐Haack Jochen 
Published: April 2003

AbstractLinear polybiurets can be synthesized by polycondensation of chloroformyl isocyanate and N,N′‐bis(trimethylsilyl)‐α,ω‐diaminoalkanes or silylated aromatic diamines. The polybiurets were characterized by elemental analyses, inherent viscosity measurements, IR spectroscopy, 1H, 13C, 15N NMR spectroscopy in solution, differential scanning calorimetry (DSC) measurements, wide‐angle X‐ray scattering (WAXS) and thermogravimetric analyses. All polybiurets are semicrystalline materials with a low rate of crystallization and unexpectedly low melting points. 13C and 15N NMR cross‐polarization/magic angle spinning (CP/MAS) spectra of the solid polybiurets indicate different conformations for the amorphous and crystalline phase. All polybiurets gradually decompose upon heating above 200°C. Synthetic methods and properties of linear biurets were also checked by synthesis and characterization of N,N′‐dioctylbiuret.
Synthesis and polymerization of epoxymethacrylates, 1. Catalysis and kinetics of the addition reaction of methacrylic acid and 2,2‐bis[4‐(2,3‐epoxypropoxy)phenyl]propane
Authors: Sandner Barbara , Schreiber Ramona 
Published: April 2003

AbstractThe kinetics of the addition reaction of methacrylic acid (1) and 2,2‐bis[4‐(2,3‐epoxypropoxy)‐phenyl]propane catalyzed by tertiary aliphatic amines, aromatic N‐heterocycles and quaternary ammonium salts, respectively, was studied in bulk with equimolar amounts of functional groups from room temperature to 120°C. A reaction order of 1,5 with regard to the conversion of epoxy as well as carboxylic groups was observed. This can be explained assuming the formation of an ammonium alkoxide ion pair by the equilibrium reaction of an epoxy group with ammonium carboxylate and the irreversible consecutive reaction of the ion pair with (1) under formation of 2‐hydroxyester groups and regeneration of ammonium carboxylate. The reaction rate constants increase linearly with the concentration of the catalyst and increase with increasing basicity of alkylpyridines. The advantage of the aromatic N‐heterocyclic catalysts consists in their stability to peroxides which are ingredients of preparations together with the epoxy methacrylate Bis‐GMA, e. g. in dental composites and adhesives.
Local mobility and liquid‐crystalline state in side‐chain polymers with mesogenic groups directly bonded to the main chain
Authors: Nikonorova Natalia A. , Stepanova Tamara P. , Malinovskaja Vera P. , Burstein Lija L. , Borisova Tamara I. , Korshun Alexander M. , Skorochodov Sergei S. 
Published: April 2003

AbstractThe intramolecular mobility of copolymers 4 was investigated by means of dielectrospectroscopy. The copolymers exhibit a convenient model for the study of local mobility in side‐chain thermotropic polymers without spacer. The dependencies of the dielectric losses on frequency and temperature point to the presence of relaxation processes related to the intramolecular mobility of fragments of the mesogenic group. For the formation of the liquid‐crystalline state two factors are important: different forms of local mobility inside the mesogenic groups and a flexible connection between side chain and main chain.
Emulsion polymerization of styrene using phospholipids with polymerizable chain as an emulsifier
Authors: Watanabe Shinji , Ozaki Hiroyuki , Mitsuhashi Ken‐ichi , Nakahama Seiichi , Yamaguchi Kazuo 
Published: April 2003

AbstractEmulsion polymerizations of styrene with various phospholipids as emulsifiers were carried out to obtain latices bearing the lipids. Using 1‐palmitoyl‐2‐(4‐vinylbenzoyl)‐sn‐glycero‐3‐phospho‐choline (2a) and 1‐[5‐(4‐vinylphenyl)pentanoyl]‐sn‐glycero‐3‐phosphocholine (3) as emulsifiers, latices of narrow size distributions were produced in high yields with a water‐soluble initiator, K2S2O8. The lipids were found to be quantitatively immobilized onto the latex surface. With a hydrophobic initiator, 1‐palmitoyl‐2‐[5‐(4‐vinylphenyl)pentanoyl]‐sn‐glycero‐3‐phosphocholine (2c) were bound densely on the latex surface, although the yields were not high. Phospholipase C was found to hydrolyze 2b and 2c attached to the surface.
On the kinetics of polymerization and copolymerization of poly(oxyethylene) macromonomers and styrene
Authors: Capek Ignac , Riza Medyan , Akashi Mitsuru 
Published: April 2003

AbstractThe homogeneous and the dispersion polymerzation and copolymerization of methacryloyl‐terminated poly(oxyethylene) (MMA‐PEG) and of p‐vinylbenzyl‐terminated poly(oxyethylene) (St‐PEG) macromonomers and styrene, initiated by a radical initiator, was investigated using conventional gravimetric and NMR methods at 60°C. The batch polymerizations in N,N‐di‐methylformamide and in ethanol/water were conducted to either low or high conversion. The fractional conversion rates of the solution polymerization and copolymerization indicate that the homopolymerizations of macromonomers involve steady‐state conditions, whereas copolymerizations proceed under non‐stationary conditions. The ratios of the rate constants for propagation and termination (kp/k) for polymerization and copolymerization of MMA‐PEG and St‐PEG are by one order of magnitude higher than that for styrene. The increase in kp/k is more pronounced in dispersion polymerization, which is ascribed to the decrease of both kp and kt. The rates of dispersion polymerization are proportional to the particle concentration. The number of particles increses up to 50% conversion. The particle growth is suggested to proceed via association of partcles and by propagation within polymer particles. The decrese of the number of radicals per particles as conversion proceeds is ascribed to the decrese of the growing radical activity and to the transfer of monomeric radicals to the continuous phase. The molecular weights correlate inversely with the particle size.
Synthesis of new polymers via Diels‐Alder reaction, 2. Soluble polymers via copolymerization
Authors: Kuhrau Martin , Stadler Reimund 
Published: April 2003

AbstractA series of copolymers are synthesized by repetitive Diels‐Alder polyaddition reaction of bifunctional cyclohepta‐1,3,5‐trienes with bifunctional 1,2,4‐triazoline‐3,5‐diones. The copolymers of different bistriazolinediones with a bisdiene, or of different biscycloheptatrienes with a dienophile, have good solubility in CH2Cl2 and CHCl3, while the homopolymers are poorly soluble. The copolymers were characterized by standard analytical techniques to test the structural regularity of these systems. Due to the kinetic control, it is possible to apply copolymerization statistics to these systems. Based on a model study, it is concluded that alipatic and aromatic bistriazolinediones have the same reactivity towards ditropyl. Nonstoichiometric polyaddition with a slight excess of bistriazolinedones provides a possibility to prepare telechelics with highly reactive triazolinedione end‐groups. The end‐group concentration can be checked by UV spectroscopy. These telechelics are efficient bulky blocks to prepare two‐component networks with a variety of polydienes.
Preparation of 4‐nitrophenyl carbonate esters of poly‐ [5N‐(2‐hydroxyethyl)‐L‐glutamine] and coupling with bioactive agents
Authors: Marre Anne De , Schact Etienne 
Published: April 2003

AbstractPoly[N‐(2‐hydroxyethyl)‐L‐glutamine] (PHEG) is a suitable carrier for the design of macromolecular prodrugs. A method is described for partial conversion of hydroxyl side groups into reactive carbonate esters. Activation is achieved through the reaction with 4‐nitrophenyl chloroformate. It is shown that during the course of the activation no intra‐ or intermolecular carbonate esters are formed. The content of reactive carbonates can, for a given set of reaction conditions, be controlled by the amount of chloroformate added. The activated polymer easily reacts with numerous amines. Reaction with a melphalan prodrug and amino‐terminated glycosides demonstrated the feasibility of the presently described activation method to prepare macromolecular prodrugs.
Cationic polymerization of bis(1‐alkylvinyl)benzenes and related monomers, 6. Improved synthesis of polyindanes
Authors: Maier Gerhard , Leitner Michael B. , Nuyken Oskar 
Published: April 2003

AbstractReaction conditions have been found which allow the synthesis of polyindanes with improved molar mass. The properties of four different polyindanes are described and compared with those of polyindanes with low molar mass from former investigations. The range of glass transition temperatures which can be achieved with polyindanes has been extended from − 10°C to 293°C. In addition, one of the newly snythesized polyindanes exhibits crystallinity with a melting point of 253°C. This is in sharp contrast to all other polyindanes investigated up to now, which were completely amorphous.
Iodine‐poly(vinyl alcohol) interactions, 5. Releasing mechanism of I− and I2 in the decomposition process of the blue complex
Authors: Yokota Toshio , Kimura Yoshiharu 
Published: April 2003

AbstractBy treating a blue‐colored solution of poly(vinyl alcohol) (PVA), iodine and boric acid with an anion exchange resin, a solution consisting only of the polyiodide ion bound to the PVA matrix was obtained. In order to re‐establish the equilibrium between polyidodide, I2 and I−, the bound polyiodide ions decomposed to I− and I2. When this happend at temperatures below 10°C, only I− was released from the PVA matrix with I2 remaining in it, and a new equilibrium state was reestablished. However, above 20°C all polyiodide ions were decomposed without recovering the equilibrium of the reaction. In this case both I2 and I− were released from the PVA matrix. Based on these findings a new mechanism for the formation and decomposition of polyiodide ions was deduced. From the initial and equilibrium concentrations of the polyiodide ions at 5 and 10°C, approximate dissociation constants to I− (free) and I2 (bound) were estimated.
Enhanced crystallization by annealing of poly(phenylene sulfide) in presence of CO2 and N2O
Authors: Schultz Joachim Dirk , Böhning Martin , Springer Jürgen 
Published: April 2003

AbstractCrystallization of amorphous poly(phenylene sulfide) was carried out upon annealing in the presence of sorbed CO2 and N2O at pressures of 50 bar. Thermal crystallization at the same pressure allows the comparison of crystallization rates. From the results of IR‐spectroscopy, wide angle X‐ray diffraction, differential scanning calorimetry and density measurements, it is seen that in the presence of sorbed gas molecules crystallization occurs even at temperatures below the glass transition measured at atmospheric conditions. At a given temperature, gas sorption yields accelerated crystallization. The results, show the considerable plasticizing influence of sorbed gas molecules. From the crystallization rate at sorbed gas conditions the plasticizing ability of the gas may be estimated. That of N2O exceeds that of CO2 by a factor of three. Assuming a simple two‐phase model for the crystalline polymer the comparison of heat of melting and density values for t → ∞ allows the conclusion that parts of the noncrystalline volume fraction become less dense by annealing in the presence of sorbed gas molecules. An increased free volume fraction which may be formed in the non‐crystalline regions is discussed. It is possible that the remaining lower density results from a hindered relaxation of chain molecules from the dilated state they take due to gas sorption. In this context the influence of decreased mobility of non‐crystalline chains is discussed in terms of the “rigid amorphous phase” concept.
Esterification and amidation of polymeric acyl chlorides. A new route to polymethacrylates and polymethacrylamides with a variety of different side groups
Authors: Strohriegl Peter 
Published: April 2003

AbstractThis paper describes the synthesis of a number of polyacrylates, polymethacrylates and polymethacrylamides by polymer analogous esterification or amidation of polymeric acyl chlorides. The reactive prepolymers are accessible by free‐radical polymerization of acryloyl or methacryloyl chloride. Prepolymers with a reduced amount of reactive groups were prepared by copolymerization of methacryloyl chloride and methyl methacrylate. Polymer analogous esterification of the prepolymers leads to polyacrylates and polymethacrylates with azobenzene, carbazole and azosulfonate side groups. The synthesis of some polymethacrylates with NLO‐active side groups including photocrosslinkable materials is also described.
Structural variations as a function of temperature and dynamic‐mechanical relaxations for ethylene‐tetrafluoroethylene and ethylene‐chlorotrifluoroethylene alternating copolymers
Authors: Guerra Gaetano , De Rosa Claudio , Iuliano Mauro , Petraccone Vittorio , Corradini Paolo , Ajroldi Giuseppe 
Published: April 2003

AbstractThe X‐ray diffraction patterns at different temperatures of alternating ethylene‐tetrafluoroethylene (ETFE) and of alternating ethylene‐chlorotrifluoroethylene (ECTFE) copolymer samples are compared. For ECTFE, a reversible variation with temperature of the half‐width of the diffraction peaks, analogous to but much smaller than that one which corresponds to the topotactic crystal‐to‐crystal transition of ETFE, was found. A comparison of the dynamic mechanical spectra of the two copolymers seems to confirm the different nature of the two high‐temperature relaxation peaks. In particular, the so called α and β relaxations of ECTFE occur in the amorphous phase while the so called α and α′ relaxations of ETFE occur in the amorphous and crystalline phase, respectively.
Structure and behaviour of SiO2/MgCl2 bisupported Ziegler‐Natta catalysts for olefin polymerization
Authors: Lu Honglan , Xiao Shijing 
Published: April 2003

AbstractBisupported catalysts for olefin polymerization were prepared by mixing a butyl alcoholate solution of MgCI2 with pretreated SiO2 in heptane, and further treating with TiCI4 solution. The silica pretreating conditions and their effects on the composition of the catalysts were studied. The interaction mechanism of the two supports, MgCI2 and SiO2, is discussed. The effect of the composition and the structure of the catalyst on the behaviour of ethylene and propylene polymerization is described. The calcination temperature of SiO2 has a significant effect on composition, structure and properties of the catalysts. There exist both chemical bonding and physical absorption between SiO2 and MgCI2 supports. The activities for propylene polymerization remarkably increase with increasing mole ratio Mg/Ti of the catalysts, while for ethylene polymerization, the activities mainly depend on the Ti content of the catalysts and the calcination temperature of SiO2 used.
Liquid crystalline polyacrylates containing biphenyl and chiral terminal groups in the side chain, 2. Influence of the nature of the chiral group
Authors: Tabrizian Maryam , Bunel Claude , Vairon Jean‐Pierre , Friedrich Claude , Noël Claudine 
Published: April 2003

AbstractAcrylate monomers with a chiral group have been synthesized bearing a propyl, isopropyl or benzyl substituent on the asymmetric carbon. All of the monomers are crystalline. Above their melting point, they give a clear, isotropic melt. The corresponding polymers have been prepared by free radical polymerization. They were examined by differential scanning calorimetry, optical microscopy and X‐ray diffraction. They were found to show a reproducible liquid‐crystal behavior. On cooling from the isotropic state, SA, S (or S) and crystal‐like (probably SH or SH′) phases become evident. Our results do not preclude the existence of a S phase between the SA and S phases. It is noteworthy that polyacrylates of the same series but with side chains terminated by a chiral group bearing a methyl substituent exhibit SA, SB and crystal‐like (probably SE) phases.