bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relationship between structure and gas permeation properties of polyimides prepared from oxydiphthalic dianhydride
Authors: Li Yuesheng , Ding Mengxian , Xu Jiping 
Published: April 2003

AbstractGas permeability coefficients of a series of aromatic polyimides, which were prepared from oxydiphthalic dianhydride (ODPA) with various aromatic diamines, with respect to H2, CO2, O2, N2, and CH4 were measured under 10 atm and in the temperature range from 30 to 150°C. A significant change in gas permeability and permselectivity resulting from systematic variation of the chemical structure of the polyimides was found. Among the polyimides which were prepared from phenylenediamine and its derivatives as well as bridged diamines without side groups on the benzene rings of the diamine residues, the increase of the gas permeability is accompanied by a decrease of the permselectivity. However, both the gas permeability and the permselectivity of the polyimides which were prepared from bridged diamines with methyl or methoxy groups on the benzene rings of the diamine residues simultaneously increase.
Influence of the molecular structure on the dynamics in poly(ester‐imide)s
Authors: Abdallah Merenga , Groothues Herbert , Kremer Friedrich , Kricheldorf Hans R. 
Published: April 2003

AbstractDielectric spectroscopy in the frequency range from 0.1 to 105 Hz was employed to study the molecular dynamics of main‐chain poly(ester‐imide)s (PEIMs) with varying spacer lengths from 5 to 12 methylene units. For all samples three relaxation processes were observed. The β‐process shows an Arrhenius‐like temperature dependence with activation energies between 50 and 55 kJ/mol. This process is assigned to a local libration of the ester groups. The α*‐process shows a WFL‐like temperature dependence. It is assigned to a main‐chain‐coupled motion of the mesogens around their short molecular axes. The α‐process also follows a WFL‐like temperature dependence. It is assigned to cooperative main‐chain motion of PEIM and it is correlated to the glass transition.
Radical polymerization of a trimer of methyl acrylate as polymerizable α‐substituted acrylate
Authors: Kobatake Seiya , Yamada Bunichiro 
Published: April 2003

AbstractThe radical polymerization of a trimer of methyl acrylate was investigated in relation to the steric hindrance‐assisted polymerization of an α‐(substituted methyl)acrylic ester. The trimer can also be regarded as a model of the unsaturated end group formed by the addition‐fragmentation chain transfer of methyl α‐(bromomethyl)acrylate during methyl acrylate polymerization. The trimer polymerizes slowly to a low‐molecular‐weight polymer at 30–60°C, and electron spin resonance (ESR) quantification of the propagating radical of the trimer allowed the determination of the absolute rate constants of propagation (kp) and termination (kt). The kp and kt values for the trimer indicate slow propagation and slow termination of polymerizable acrylates bearing a bulky α‐substituent. In conformity with a higher reactivity of the trimer of methyl acrylate than the corresponding trimer of methyl methacrylate, poly(methyl acrylate) bearing an unsaturated end group, which is produced by the polymerization of methyl acrylate in the presence of methyl α‐(bromomethyl)acrylate, was confirmed to copolymerize with methyl acrylate to yield a branched homopolymer.
Synthesis, characterization and photoreaction of side‐chain liquid‐crystalline polymers and copolymers comprising alkenyloxy‐biphenyl mesogen
Authors: Kawatsuki Nobuhiro , Takatani Ken , Yamamoto Tohei , Sangen Osamu 
Published: April 2003

AbstractPhotoreactive (meth)acrylate monomers having mesogenic groups based on 4‐hexyloxy‐4′‐(3‐methyl‐2‐butenyloxy)biphenyl and 4‐hexyloxy‐4′‐(2‐butenyloxy)biphenyl were synthesized. Methacrylate monomers (3c, d) and acrylate monomer having 3‐methyl‐2‐butenyloxy group (3b) were polymerized by free radical mechanism; the acrylate monomer having 2‐butenyloxy group (3a) caused gelation during the polymerization. To obtain photoreactivity, 4‐benzoylphenyl (meth)acrylates were radically copolymerized with monomers 3b and 3d. Thermal behavior of (co)polymers was determined by differential scanning calorimetry, polarized optical microscopy and temperature‐controlled X‐ray analysis. (Co)polymers showed liquid‐crystalline behaviour with nematic and smectic phases. UV‐irradiation was used to photochemically crosslink copolymer films, and the resultant films were insoluble in organic solvents. The uniaxially oriented copolymer thin film was photo‐crosslinked and showed thermally stable orientation.
Complexation of polyacrylamide and poly(N‐isopropylacrylamide) with poly(acrylic acid). The temperature effect
Authors: Staikos Georges , Karayanni Katerina , Mylonas Yannis 
Published: April 2003

AbstractWe present potentiometric and viscometric results on the interpolymer complexation between polyacrylamide (PAAM) and poly(N‐isopropylacrylamide) (PNIPAAM) with poly(acrylic acid) (PAA) in dilute aqueous solution. A potentiometric procedure for the determination of the complex stoichiometry in monomeric units has been proposed. The temperature dependence of the strength of the complex formed has been investigated. From the results obtained it has been concluded that hydrogen bonding is the main factor stabilizing the PAAM/PAA complex, strengthened by decreasing the temperature while the much stronger PNIPAAM/PAA complex, strengthened by increasing the temperature, is stabilized by hydrophobic interaction.
Coordinative polymerization of p‐substituted phenyl glycidyl ethers, 1. Effect of electron‐donating groups
Authors: Ronda Joan Carles , Serra Angels , Cádiz Virginia 
Published: April 2003

AbstractA series of p‐substituted glycidyl phenyl ethersIUPAC nomenclature: 2,3‐epoxypropyl phenyl ether.
with electron donor groups was prepared using a multistep synthetic method. These compounds were polymerized using four of the most common aluminium‐based coordinative initiators, (C2H5)3Al/H2O (the Vandenberg catalyst), (C2H5)3Al/CH3COCH2COCH3/H2O (the Vandenberg chelate catalyst), [(CH3)2CHO&&rsqb;2AlOZnOAl[OCH(CH3)2]2 (the Teyssié catalyst) and [(CH3)2CHO]3AV/ZnCI2 (the Price catalyst), all with different Lewis acid character. The influence of the electron‐donor group on the characteristics and conversion was studied. Generally speaking, both the Vandenberg and the Teyssié catalysts yield mostly an insoluble polymer fraction, whereas the Price catalyst was shown to be the most stereoselective catalyst. Moreover, the Vandenberg chelate catalyst gave the highest molecular weight, the Price catalyst the lowest. Thermal characteristics of polymers were studied by means of differential thermal analysis to obtain glass transition temperatuures, melting temperatures and fusion enthalpies.
Coordinative polymerization of p‐substituted phenyl glycidyl ethers, 2
Authors: Ronda Joan Carles , Serra Angels , Cádiz Virginia 
Published: April 2003

AbstractAs a complementary study of a previous work about the influence of the electronic effects of p‐substituted phenyl glycidyl ethers on the polymerization behaviour, a new series of monomers with electron‐withdrawing groups was prepared, i.e., highly reactive p‐functionalized poly(phenyl glycidyl ethers) were prepared. The polymerizations were carried out with four different aluminium‐based coordinative initiators, (C2H5)3Al/H2O (mole ratio 1:0.6) (the Vandenberg catalyst), (C2H5)3Al/CH3COCH2COCH3/H2O (mole ratio 1:1:0.5) (the Vandenberg chelate catalyst), [(CH3)2CHO]2AlOZnOAl[OCH(CH3)2]2 (the Teyssié catalyst) and [(CH3)2CHO]3Al/ZnCl2 (the Price catalyst), all with different Lewis acid character. The influence of the electron withdrawing groups on the characteristics and conversion of polymers was studied. All polymers were characterized by nuclear magnetic resonance spectroscopy showing higher tacticities when the Price catalysts was used. In some cases the degree of conversion was low due to passivation effects which were studied in several experiments.
On the polymer effect observed with macromolecular photoinitiators: A study of the viscosity effect on the starting polymerization rate
Authors: Leclercq Pascal , Buisine Jean‐Marc , Coqueret Xavier 
Published: April 2003

AbstractPhotopolymerizable acrylate compositions including small amounts of poly(butyl acrylate) were submitted to photocalorimetric measurements in order to investigate the effect of the mixture viscosity at zero conversion on the initial polymerization kinetics. No significant change of the initial polymerization rate profile was observed for starting viscosities ranging between 4 and 36 mPa · s and for a given concentration of low molecular weight photoinitiating system of the benzophenone‐amine type. This demonstrates that the polymer effect that leads to a higher value of the initial polymerization rate (Rp)0 when using an analogous photoinitiating system with the same content in polymeric benzophenone chromophores cannot be ascribed to the higher viscosity at zero conversion that results from the presence of the photosensitive macromolecules.
The conformational coil‐globule transition of polystyrene in cyclohexane solution
Authors: Vshivkov Sergei A. , Safronov Alexander P. 
Published: April 2003

AbstractThe phase diagram of a monodisperse high molecular weight polystyrene (Mw = 3.3 · 106, Mw/Mn < 1.06) solution in cyclohexane was thoroughly studied by means of light scattering, cloud point, coexisting phases volume ratio, coexisting phases composition and scanning calorimetry methods, and binodal and spinodal curves were obtained. Coordinates of the UCST (T = 306.2 K, ϕ2 = 1.88 · 10−2) determined by different methods were similar. It was found that the first‐order phase transition curve obtained by calorimetric scanning at 10−6 K/s accurately fits the spinodal of the system within the concentration range of semidilute and concentrated solutions and has a horizontal part in dilute solutions where the temperature of phase transition was found to be 303.86 K, independently of concentration. At the same temperature a deflection point was found on the concentrated branch of the spinodal. The results were taken as calorimetric evidence of a coil‐globule phase transition in the polystyrene solution. It was shown that the collapse of the polystyrene coils takes place in the metastable system between the binodal and the spinodal in the same way as in the homogeneous solution above the binodal.
A new kinetic interpretation of the styrene microemulsion polymerization
Authors: Nomura Mamoru , Suzuki Kiyoshi 
Published: April 2003

AbstractThe polymerization of styrene initiated by potassium peroxodisulfate was conducted at 50°C in oil‐in‐water microemulsions using sodium lauryl sulfate and 1‐pentanol as emulsifier and cosurfactant, respectively. Based on the experimental findings that both particle size and molecular weight of the polymers are almost independent of styrene conversion and the initial initiator concentration, a kinetic scheme of the microemulsion polymerization of styrene is proposed, which assumes that (1) particle nucleation occurs in monomer‐swollen micelles and almost all the radicals in the water phase enter the monomer‐swollen micelles and finally initiate polymerization therein, (2) with negligible radical termination in the water phase and (3) with negligible radical entry into the preformed polymer particles, and accordingly, (4) all chain‐stopping events in the active polymer particles are chain transfer reactions to monomer. Based on this kinetic scheme, a simple kinetic model is proposed, which can explain fairly well the progress of styrene microemulsion polymerization in the initial stage.
Living polymerization of substituted acetylenes by a novel ternary catalyst, MoOCl4Et2ZnEtOH
Authors: Hayano Shigetaka , Masuda Toshio 
Published: April 2003

AbstractA novel molybdenum oxytetrachloride (MoOCl4)‐based ternary catalyst, molybdenum oxytetrachloride/diethylzinc/ethanol (MoOCl4Et2ZnEtOH), induces the living polymerization of o‐(trifluoromethyl)phenylacetylene. A catalyst composition of MoOCl4:Et2Zn: EtOH (mole ratio = 1:1:3) and anisole as polymerization solvent are favorable. The ratio of weight‐ to number‐average molecular weights Mw/Mn of the polymer was as small as 1,03, and the initiator efficiency was 8%. Living polymerization was verified by multistage polymerization. The polymerization proceeded in a living fashion in the temperature range from 0 to 30°C. The catalyst yielded polymers with small Mw/Mn values also from other phenylacetylenes with bulky ortho substituents and 1‐chloro‐1‐octyne.
Polyurethane networks based on α,ω‐dihydroxytelechelic and on random hydroxyl‐functionalized side chain poly(2‐chloroethyl vinyl ether)s: Synthesis and investigation of mechanical properties
Authors: Bennevault Véronique , Richard Gilles , Deffieux Alain 
Published: April 2003

AbstractThis paper reports on the synthesis and characterization of polyurethane networks based on an α,ω‐dihydroxytelechelic poly(2‐chloroethyl vinyl ether) (PCEVE precursor, type I) and on PCEVE with 2‐hydroxyethyl groups statistically distributed along the chains (PCEVE precursor, type II). The different hydroxyl‐functional polymer precursors were synthesized via “living” cationic polymerization of CEVE to allow the control of molecular weights, molecular weight distributions, as well as, for the dihydroxytelechelic precursor, the chain end functionality. PCEVE precursors of type II were obtained by derivatization of a small fraction of 2‐chloroethyl side groups into 2‐hydroxyethyl groups, using polymer analogous reactions.The mechanical properties of the corresponding PCEVE‐polyurethane (PU) networks were investigated. Data are analyzed in terms of precursor structure and average chain length between crosslinks. The mechanical properties of the PCEVE‐PU networks are also compared to those of PU networks based on hydroxyl‐terminated polybutadiene (HTPB) prepared according to the same experimental procedure. It was found that the networks based on PCEVE have higher toughness to break and higher elongation properties.
Polymers from coumarins, 3. Design and synthesis of novel fully aromatic coumarin‐containing polyesters
Authors: Fomine Serguei , Delgado Carmen , Fomina Lioudmila , Gaviño Ruben , Ogawa Takeshi 
Published: April 2003

AbstractA novel coumarin‐containing monomer 6‐[4‐acetoxyphenyl]coumarin‐3‐carboxylic acid (5) was prepared and characterized. It was copolymerized by high‐temperature polycondensation with m‐acetoxybenzoic acid (11) to give copolymers with Mn of 5 300–18 000, soluble in common organic solvents and containing up to 40 mol‐% of monomer 5. All copolymers were amorphous, with Tg increasing with monomer 5 ratio (from 147 to 162°C) and high optical quality films preparable by solution casting from chloroform. All polymers show strong photoemission in the blue‐green region and some of them present electroluminescence.
Ethylene polymerizations with disiloxane‐bridged indenyl and cyclopentadienyl metallocene catalysts
Authors: Wang Baiquan , Su Liming , Xu Shansheng , Feng Ru , Zhou Xiuzhoug , He Dawei 
Published: April 2003

Abstractansa‐Tetramethyldisiloxane‐bridged indenyl, tetrahydroindenyl and cyclopentadienyl zirconium complexes 1–4 were prepared. The pure rac‐1–3 and meso‐1–2 complexes were separated by fractional crystallization. Indenyl complexes, both rac‐1 and meso‐1, in the presence of methylaluminoxane (MAO), have very high activities for ethylene polymerization. The molecular weight of polyethylene produced with rac‐1 is extremely high and significantly dependent on polymerization temperature. The tert‐butyl‐substituted cyclopentadienyl complex exhibits low activity and produces polyethylene of low molecular weight.
Copolymerization of poly(propylene) macromonomer with ethylene by (tert‐butanamide)dimethyl(tetramethyl‐η5‐cyclopentadienyl)silanetitanium dichloride/methylaluminoxane catalyst
Authors: Shiono Takeshi , Moriki Yuji , Ikeda Tomiki , Soga Kazuo 
Published: April 2003

AbstractThe copolymerization of ethylene and a poly(propylene) macromonomer, the number‐average polymerization degree (Pn) of which was about 11, was conducted with (tert‐butanamide)dimethyl(tetramethyl‐η5‐cyclopentadienyl)silanetitanium dichloride (CGC‐Ti) combined with methylaluminoxane. The rate of ethylene consumption is increased by adding the macromonomer when copolymerization was carried out at 40°C, whereas such rate enhancement could not be observed at 90°C. It was found that the increase of ethylene polymerization rate is accompanied by the incorporation of the macromonomer. Based on differential scanning calorimetry (DSC) and 13C NMR measurements of the produced polymers, it was proved that the poly(propylene) macromonomer was copolymerized with the present CGC‐Ti catalyst and the Pn value of the macromonomer incorporated in the copolymer does not influence the conversion of the macromonomer.
Polyelectrolyte multilayers containing photoreactive groups
Authors: Laschewsky André , Wischerhoff Erik , Bertrand Patrick , Delcorte Arnaud 
Published: April 2003

AbstractThe synthesis of a photocrosslinkable polycation and its use in the assembly of alternating polyelectrolyte multilayers are described. Characterization by UV/VIS spectroscopy and time‐of‐flight secondary ion mass spectroscopy (ToF‐SIMS) reveals the influence of the crosslinking on the physical properties of the build‐ups. Remarkably, the assembly of such multilayer structures is not only possible on hydrophilic substrates, but also on apolar poly(propylene). In this case, the crosslinkable polycation turns out to be especially useful to obtain stable, solvent resistant coatings.
Synthesis and characterization of poly[3‐(6‐tetra‐hydropyran‐2‐yloxyhexyl)‐2,5‐thienylene]
Authors: Bolognesi Alberto , Mendichi Raniero , Schieroni Alberto , Villa Daniela , Ahumada Oscar 
Published: April 2003

AbstractThe synthesis of poly[3‐(6‐tetrahydropyran‐2‐yloxyhexyl)‐2,5‐thienylene] has been performed with a nickel catalyst, obtaining a highly regioregular polymer. The deprotection of the pyranyl function restores the OH group giving a polymer which is not soluble in the usual organic solvents but soluble in 1‐methyl‐2‐pyrrolidone, indicating that no crosslinks are present. The protected form was characterised by means of GPC, 1H NMR, FTIR and UV‐Vis spectroscopy and was found to give Langmuir‐Blodgett multilayered structures.
Zur Katalyse der stereospezifischen Butadienpolymerisation mit den Katalysatorsystemen aus Nd(η3‐C3H5)3 · dioxan und methylaluminoxan (MAO) sowie Hexaisobutylaluminoxan (HIBAO)
Authors: Maiwald Steffen , Weißenborn Helga , Windisch Heike , Sommer Christian , Müller Gert , Taube Rudolf 
Published: April 2003

AbstractThe activation of the tris(allyl)neodymium complex Nd(η3‐C3H5)3 · dioxane with alkylaluminoxanes (MAO or HIBAO) results in highly selective catalysts for the 1,4‐cis‐polymerization of butadiene (cis‐selectivity up to 80%). Under standard conditions (50°C, toluene), the turnover frequency (TOF) of the catalyst/MAO system amounts to 10–15000 mol butadiene/(mol Nd · h). Molecular weight determinations indicate the formation of only one polymer chain per neodymium center as in a living polymerization reaction, and for the catalyst/HIBAO system the rate law rp = kp [Nd][C4H6] with kp = 8,7 · 10−2 mol/(L · s) (at 25°C) has been derived. As the catalytically active species, a cationic monobutenyl neodymium(III) complex is discussed, which is stabilized through coordinative interaction with the counter anion as well as the growing polybutadiene chain. This cationic complex reacts under insertion with butadiene in a bimolecular fashion.
A novel orientation material for liquid crystals based on modified ladder‐like polysiloxanes
Authors: Tang Yongxing , Cui Li , Xie Ping , Zhang Rongben , Zhang Zhiyong , Wan Boquan 
Published: April 2003

AbstractA new orientation material for liquid crystals (LCs) based on modified ladder‐like polysiloxanes (LPSs) is investigated. The curing temperature (150–200°C) of these grafted LPSs is much lower than that of the traditionally used polyimides (PIs) (250–300°C). The pre‐tilt angles of a nematic liquid crystal (LC), 4‐pentyl‐4′‐cyanobiphenyl (5CB), are between 2–8°, depending on the rubbing conditions and the side chains. Annealing experiments at 100°C and 180°C demonstrated that the stability of these orientation films is quite well.
Gelation of aqueous solutions of diblock copolymers of ethylene oxide and D,L‐lactide
Authors: Tanodekaew Siriporn , Godward John , Heatley Frank , Booth Colin 
Published: April 2003

AbstractThe thermally‐reversible gelation of aqueous solutions of diblock copolymers of ethylene oxide (E) and D,L‐lactide (L), E42L12, E38L16, E39L20, E41L26, E78L14 and E77L26, has been studied using gelation temperature measurements, polarised light microscopy and NMR spectroscopy. The solutions showed a high temperature gel‐sol boundary but no low temperature gel‐sol boundary. Polarised light microscopy showed that the gel phase was isotropic, and the dependence of sol‐gel temperature on concentration suggested that the micelles were prolate ellipsoidal, rather then spherical. NMR spectroscopy showed that below ca. 60°C, the L block in the micelle core become highly restricted. It is tentatively suggested that this is due to the L blocks forming an ordered structure, thus explaining the absence of a low temperature gel‐sol boundary.
Chain conformation and packing of isopentylcellulose in thin films
Authors: Fakirov Christo , Lieser Günter , Wegner Gerhard 
Published: April 2003

AbstractMultilayers of isopentylcellulose (systematic name: tri‐O‐isopentyl cellulose, IPC) were investigated by means of electron diffraction. Only the persubstituted cellulose ether showed some order in a multilayer as deposited. IPCs of lower degree of substitution (DS) form ordered layers when annealed at temperatures ≤150°C. IPC molecules adopt helix conformation; the lattices show in this temperature range 3‐fold screw axes. From analogy with known structures of cellulose derivatives we suggest left‐handed 32‐helices. At a temperature of about 210°C IPC multilayers undergo a transition into the liquid‐crystalline state and the feature of a stack of individual layers disappears. This was investigated for an IPC of DS = 3. By subsequent cooling a phase transition into a highly crystalline state takes place. From the huge increase of the crystalline density from initially 1.02 g/cm3 in the multilayer system to 1.40 g/cm3 in the bulk crystal at ambient temperature after having passed the liquid‐crystalline state we infer that the transition of the layered system into the liquid‐crystalline state is accompanied by selection of adjacent chains according to their polarity. Simultaneously the chain conformation is changed into a 4‐fold screw with 2 symmetry related chemical repeats forming the asymmetrical unit. Such a chain conformation is not known for other cellulose derivatives, only trimethylamylose adopts a similar conformation with a distorted 43‐helix.
Light‐scattering study of random disorder in liquid crystalline elastomers
Authors: Clarke S. M. , Nishikawa E. , Finkelmann H. , Terentjev E. M. 
Published: April 2003

AbstractWe report on the structural study of a non‐uniform (polydomain) director texture in nematic and smectic liquid crystalline elastomers. Polarised light scattering is used to probe the equilibrium director correlations in the region of transition under stress between the opaque polydomain material and the transparent, macroscopically monodomain elastomer. A characteristic four‐peak scattering image is obtained in this transient region. The lobes of intensity are oriented along and perpendicular to the axes of crossed polarisers, with anisotropy along the direction of principal extension. We propose a theoretical model, based on the competition between the random disordering field due to the network crosslinks and the external aligning field