bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular microstructure dependence of space charges in polymers. Coupling of thermal step (TS) and thermally stimulated discharge current (TSDC) methods in PVC after nucleophilic substitution
Authors: Guarrotxena Nekane , Vella Nathalie , Toureille Alain , Millán José‐Luis 
Published: April 2003

AbstractThe space charge distribution, a basic electrical property of insulating materials, has been studied for a poly(vinyl chloride) (PVC) sample before and after nucleophilic substitution reaction up to various degrees with sodium benzenethiolate (NaBT) in cyclohexanone (CH) solution, so as to modify in a controlled way the content of the isotactic tetrad mmr and the heterotactic pentad rrmr located at the end of isotactic and syndiotactic sequences, respectively. We investigated the influence of mmr and rrmr structures on the number and type of electrical charges accumulated in the material when submitting it to an electrical field. To differentiate between the polarization charges and the trapped charges, coupling of the “thermal step” (TS) and the “thermally stimulated discharge current” (TSDC) techniques was applied. Both types of charges were proved to be related chiefly to the conformations GTTG‐TT and GTGTT, having higher free volume and local mobility, characteristic of mmr structure.
Rheological characteristics of semi‐dilute chitosan solutions
Authors: Mucha Maria 
Published: April 2003

AbstractThe present work is concerned with experimental results on rheological characteristic properties of semi‐dilute chitosan solutions in weakly acetic acid. The flow measurements were conducted on solutions of chitosan of various deacetylation degrees DD (62.8%–86.7%) with changing experimental conditions such as concentration (up to 5 g/100 mL), temperature (20°C–41°C) and shear rate applied (up to 103s−1). Chitosan solutions behave generally as a typical non‐Newtonian shear‐thinning fluid with a characteristic n‐parameter lower than 1. The rheological n‐parameter decreases with decreasing deacetylation degree and increasing solution concentration but it increases with increasing temperature. Because of strong intermolecular hydrogen bonding even at low concentration the chitosan macromolecules have a tendency to entangle and to network formation. The density of the molecular entanglements in the chitosan solution depends on concentration, temperature and shear rate applied. An effect of the deacetylation degree on the Huggins viscosity constant related to polymer solvent interaction is found. The most important results refer to the activation energy of viscous flow found from Arrhenius plots. The dependence of the activation energy on solution concentration, shear rate and DD is discussed.
Magnesium chloride supported bis(cyclopentadienyl)titanium(IV) dichloride‐MAO catalyst for ethylene polymerization
Authors: Sarma Soumen Sen , Sivaram Swaminathan 
Published: April 2003

AbstractA novel magnesium chloride supported titanocene catalyst was synthesized using a soluble tetrahydrofuran complex of magnesium chloride. The suported catalyst polymerized ethylene with high activities in presence of methylaluminoxane. The significant feature of the supported metallocene catalyst is that it shows high polymerization activity at low Al/Ti ratio and at higher temperatures compared to soluble catalyst. The role of support in stabilizing the active species on the metallocene is discussed.
γ‐Ray‐induced post‐polymerization of a mesogenic methacrylate in the crystalline, liquid crystalline and melt phase: Reaction kinetics and molecular weight distribution
Authors: Hohn Wilfried , Beizai Kaweh , Tieke Bernd 
Published: April 2003

AbstractThe γ‐ray‐induced post‐polymerization of mesogenic 4‐methoxy‐4′‐(6‐methacryloyloxyhexyloxy)biphenyl (1) was investigated. Reaction kinetics and molecular weight distribution of the polymer were studied. Molecular weights and weight distributions were analyzed using size exclusion chromatography. Especially, effects of radiation dose, polymerization time and temperature were investigated. Post‐polymerization was found in the crystalline, liquid crystalline and melt phase. Rate of polymerization and limiting conversion to polymer increase with radiation dose, polymerization time and temperature. Samples exposed to a low γ‐ray dose of 5 kGy and subsequently polymerized in the crystalline state at 20°C, for example, only reach a limiting conversion of about 7% within 100 h, while samples exposed to a high dose of 20 kGy and polymerized in the melt at 79°C reach a limiting conversion of 85.1% within 90 s. Molecular weights increase with polymerization temperature and reach values comparable with in‐source polymerization. Different from in‐source polymerization, they are additionally affected by the parameters radiation dose and polymerization time. High molecular weights are obtained, if samples are exposed to a low radiation dose and isothermally polymerized at high temperature for a long time, while low molecular weights result from high radiation dose and short time of polymerization at low temperature, e.g., at 20°C. By carefully adjusting the reaction parameters, molecular weights can be reliably tailored in the range from 2 × 104 to 6 × 105. Polymerization at room temperature leads to a normal molecular weight distribution, while distributions are broader when the polymerization is carried out in the liquid crystalline or melt phase. The origin of the different reaction rates and molecular weights obtained under the various conditions is discussed in terms of the mobility of growing chain ends and residual monomer, which influences chain growth and termination and thus the kinetic chain length.
Formation of supramolecular aggregates by hydrogen bonding based on bispyrimidine and bisbarbituric acid
Authors: Wang Zhiqiang , Wang Liyan , Zhang Xi , Shen Jiacong , Denzinger Steffen , Ringsdorf Helmut 
Published: April 2003

AbstractHydrogen bonds between bispyrimidine and bisbarbituric acid in equal molar ratio can lead to the formation of supramolecular aggregates. This is established by TEM, IR and DSC measurements. Additionally, WAXS pattern showed that the aggregate is of laminar structure. Both the hydrolysis of this system and termination of the aggregate's growth were studied.
The X‐ray determination of the amounts of the phases in samples of isotactic poly(propylene) quenched from the melt at different cooling rates
Authors: Martorana Antonino , Piccarolo Stefano , Scichilone Francesco 
Published: April 2003

AbstractA new procedure for the determination of the amounts of phases in samples of isotactic poly(propylene) quenched at different cooling rates from the same melted polymer is described. According to the procedure, all the patterns corresponding to the same quenching series are simultaneously analyzed for the amounts of phases so that reliable phase fractions relative to the different samples of the series are achieved. The analysis of the results points out that for increasing cooling rates above 30°C/s a remarkable increase of the mesomorphic phase settles, mainly at the expense of the α‐monoclinic one.
Synthesis and characterization of α‐hydroxy, α‐thiol and α‐chloroformyl oligomers of poly(butylene terephthalate)
Authors: Boutevin Bernard , Khamlichi Mohammed , Lusinchi Jean Marie , Robin Jean‐Jaques 
Published: April 2003

Abstractα‐Hydroxy and α‐chloroformyl oligomers of poly(butylene terephthalate) (PBT) were prepared in 1,1,2,2‐tetrachloroethane by condensing terephthaloyl chloride and 1,4‐butanediol and using benzoyl chloride and 4‐hydroxybutyl benzoate as chain limitator. The average molecular weight was determined by 1H NMR analysis, and thermal properties were assessed by differential scanning calorimetry (DSC). Preparation of α‐thiol oligomers of PBT was also investigated by esterification of α‐hydroxy oligomers with thioglycolic acid and using p‐toluenesulfonic acid as catalyst. The DSC and TGA analyses pointed out that the introduction of a thiol group by esterification has no influence on the thermal properties of the PBT oligomers.
Structure and physicochemical properties of the aldol and vinylene forms of poly(2,5‐heteroarylenevinylene)s
Authors: Kreja Ludwik , Kurzawa Marzana , Kurzawa Jacek 
Published: April 2003

AbstractWe determined the structure and physicochemical properties of poly(2,5‐furylenevinylene), poly(2,5‐thienylenevinylene) and poly(2,5‐furylene‐co‐2,5‐thienylenevinylene) that were synthesized via aldol polycondensation. Two kinds of polymer were obtained, one with mainly aldol and one with mainly vinylene structure units. The former are soluble in water, and the latter insoluble in water and only slightly soluble in organic solvents. The aldol polymers can be transformed to vinylene polymers by thermal dehydration. The d.c. conductivities at room temperature are of the order of 10−12 and 10−8 S/cm for the aldol and vinylene forms, respectively.
γ‐Ray polymerization of lyotropic solutions of cellulose derivatives under retention of the macroscopic order
Authors: Hohn Wilfried , Tieke Bernd 
Published: April 2003

AbstractTwo new lyotropic solutions of cellulose derivatives are reported which can be polymerized upon γ‐irradiation. The first solution consists of hydroxypropylcellulose (HPC) in N,N‐dimethylacrylamide (DMAcr) and the second of 2‐(acryloyloxy)propylcellulose (APC; degree of substitution (DS) = 0.18) in water. Both solutions were characterized using refractive index measurements, polarizing microscopy and diffuse reflection spectroscopy. For solutions of HPC in DMAcr, it was demonstrated that they exhibit anisotropic phase behaviour at concentrations higher than 45 wt.‐% within a limited temperature range. Highly concentrated solutions of about 70 wt.‐% also showed cholesteric phase behaviour with iridescent colours. Upon γ‐irradiation, the solvent DMAcr rapidly polymerized. A conversion to 90% of polymer was reached at a dose of 5 kGy. Molecular composites of HPC in polymerized DMAcr were obtained in which the macroscopic order was preserved. Shear‐deformed samples were still birefringent and exhibited band textures, when viewed between crossed polarizers, and light reflection of the cholesteric samples still occurred at the same wavelength as before irradiation. The polymerized samples showed an extended temperature stability, the anisotropy being stable up to approximately 150°C. The second solution of APC in water also exhibits cholesteric phase behaviour at a concentration of 61.5 wt.‐%. Upon γ‐irradiation, the polymer chains undergo rapid cross‐linking via the reactive acrylate groups and form a network in which the cholesteric order is preserved. The cross‐linked APC films are swellable in water and retain their anisotropic order when the concentration of the solution is varied between 40 and 100 wt.‐% of APC. The materials properties of the two systems after polymerization are compared.
Synthesis and characterization of aliphatic‐aromatic poly(ether amide)s
Authors: García José M. , Álvarez Julio C. , De la Campa José G. , De Abajo Javier 
Published: April 2003

AbstractFour aromatic diamines containing aliphatic spacers and Meta and para oriented oxyphenylene rings, and their corresponding hydrochlorides, were combined with isophthaloyl chloride (IPC) and terephthaloyl chloride (TPC) to give high molecular weight polyamides by interfacial and low‐temperature solution methods. The synthesis and characterization of monomers and polymers are reported, and the differences observed in polycondensation yields, molecular weights and molecular weight distributions, as a function of the method of synthesis, are discussed. Values of number‐average molecular weight (M̄n) up to 8 × 104 g/mol and weight‐average molecular weight (M̄w) up to 1 × 105 g/mol could be measured by gel permeation chromatography using aromatic polyamide standards, and values of M̄n up to 2 × 105 g/mol and M̄w up to 3.6 × 105 g/mol by using polystyrene standards.
Preparation and polymer‐analogous reactions of a poly(vinyl sugar) with a CC bond between sugar and polymer backbone
Authors: Wulff Günter , Bellmann Susanne , Schmid Jürgen , Podzimek Stepán 
Published: April 2003

AbstractThe synthesis of a new type of poly(vinyl sugar) is described whose polymer backbone is connected with the monosaccharide unit by a C—C bond. Such polymers can be obtained by radical initiation. They show good stability in polymer‐analogous reactions in contrast to common poly(vinyl saccharides) whose sugar residues are bound to the polymeric chain by ester, ether, or glycoside bonds. Starting from 7,8‐dideoxy‐1,2;3,4‐di‐O‐isopropylidene‐α‐D‐galacto‐oct‐7‐en‐1,5‐pyranos‐6‐ulose (1) polymers (P1) could be obtained by emulsion polymerization in high yields. Reduction of the keto group of P1 proceeded quantitatively and yielded poly(7,8‐dideoxy‐1,2;3,4‐di‐O‐isopropylidene‐D,L‐glycero‐α‐D‐galacto‐oct‐7‐en‐1,5‐pyranose) (P3). In contrast to the following polymers without protecting groups these poly(vinyl ketones), which were soluble in tetrahydro‐furan and toluene, did not follow a pure GPC‐separation mechanism. The protecting groups of the poly(vinyl saccharides), either with or without keto groups, could be removed completely to give P2 and P4. The solubility of the polymers P2 with galactose‐functionalized side chains in water was limited to a weight‐average molecular weight M̄w of 1 500 000 due to association phenomena of the monosaccharide units. Reduction of the hemiacetal group and of the keto group of P2 yielded poly(1,2‐dideoxy‐D,L‐glycero‐D‐galacto‐oct‐1‐enitol) (P5) with sugar alcohol side chains instead of a cyclic monosaccharide unit. Oxidation of the hemiacetal group of P2 and P4 furnished poly(7,8‐dideoxy‐D‐galacto‐oct‐7‐en‐6‐ulosonic acid sodium salt) (P6) and poly(7,8‐dideoxy‐D,L‐glycero‐D‐galacto‐oct‐7‐enonic acid sodium salt) (P7), respectively. These polymers showed very high viscosities because of their polyelectrolyte character.
Difference in propagation rate constants between photo‐and thermal‐initiated polymerization of styrene – effects of light irradiation
Authors: Kamachi Mikiharu , Kajiwara Atsushi 
Published: April 2003

AbstractPropagation rate constants (kp) for photo‐ and thermal‐initiated radical polymerizations of styrene were determined by electron spin resonance (ESR) spectroscopy. The kp value for the former at 70°C ((420 ± 30) M−1 · S−1) was more than twice as large as that for the latter ((190 ± 10) M−1 · s−1) although the former value was almost the same as that obtained with the pulsed‐laser polymerization method. To evaluate the origin of the difference in the kp values between photo‐ and thermal‐initiated polymerization the absorption spectrum of a model of the propagating radical was measured and both the influence of the wavelength of the irradiation light on kp values and the activation energy of the photo‐initiated radical polymerization of styrene were determined. kp decreases for wave‐lengths shorter than 370 nm and is in agreement with the kp value for thermal‐initiated polymerization. No wavelength dependence of kp was obtained for dienes whose propagating radical does not absorb above 300 nm. The difference in kp values for photo‐ and thermal‐initiated polymerizations is considered to be due to the photoactivation (photoinduced excitation) of the propagating radical of styrene.
Synthesis and properties of aromatic polyamides based on 4,4′‐(1,5‐naphthalenedioxy)dibenzoic acid
Authors: Hsiao Sheng‐Huei , Chu Kuan‐Yu 
Published: April 2003

Abstract4,4′‐(1,5‐Naphthalenedioxy)dibenzoic acid (3), a novel aromatic dicarboxylic acid monomer, was prepared by nucleophilic substitution reaction of 1,5‐dihydroxynaphthalene and p‐fluorobenzonitrile in N,N‐dimethylformamide (DMF) in the presence of potassium carbonate and subsequent alkaline hydrolysis of the intermediate dinitrile, 4,4′‐(1,5‐naphthalenendioxy)dibenzonitrile. Using triphenyl phosphite (TPP) and pyridine as condensing agents, a series of novel aromatic polyamides were synthesized by direct poly‐condensation of diacid 3 and twelve aromatic diamines in N‐methyl‐2‐pyrrolidone (NMP) solution containing dissolved calcium chloride. The resulting polyamides had inherent viscosities above 1,14 and up to 4,45 dL/g. Most of these polyamides are readily soluble in polar solvents, such as NMP, DMF, and N,N‐dimethylacetamide (DMAc). Transparent, flexible, and tough films could be cast from their DMAc or NMP solutions. Most of these polymers were amorphous in nature, as indicated by their wide‐angle X‐ray diffractograms. Thermogravimetric analysis (TG) showed that all the polyamides were stable up to 450°C in both air and nitrogen atmosphere. Most of them revealed a distinct glass transition on the differential scanning calorimetry (DSC) traces in the range of 183–259°C.
Synthesis of methacrylic multi‐arm star copolymers by “arm‐first” group transfer polymerisation
Authors: Haddleton David M. , Crossman Martin C. 
Published: April 2003

AbstractMethacrylic star polymers were synthesized by the “arm‐first” method of star polymer formation by the addition of difunctional monomer, ethylene glycol dimethacrylate, to living linear poly(methyl methacrylate) as prepared by group transfer polymerisation (GTP). The effects of living polymer concentration and ratio of difunctional monomer to living polymer are discussed, and show how macromolecular design and control may be imposed on the number of arms and molecular weight of the star polymer. Diluting the difunctional crosslinking monomer with monomer has been examined with the view to establishing funtionalisation of the star core.
Differential scanning calorimetry studies on water restrained in hydroxyethylcellulose and hydrophobically modified hydroxyethylcellulose
Authors: Tanaka Ryohei , Hatakeyama Tatsuko , Hatakeyama Hyoe 
Published: April 2003

AbstractDifferential scanning calorimetric (DSC) studies were carried out for hydrophobically modified hydroxyethylcellulose (HMHEC)‐ and hydroxyethylcellulose (HEC)‐water systems to examine the binding of water with polymer molecules and the formation of a structure. The amount of freezing‐bound water in HMHEC was found to be much less than that in HEC. The above fact suggests that the water‐polymer interaction is hindered by the presence of the hydrophobes. The formation of a structure above the melting point of ice was detected by DSC for both systems HMHEC‐ and HEC‐water. Polarizing light micrographs of these two aqueous polymer systems showed the formation of a liquid crystalline state in the same range of temperature. These phenomena were observed in a wider range of water content for HMHEC (Wc <4.0) than for HEC (Wc <2.5).
Association and surface properties of diblock copolymers of ethylene oxide and DL‐lactide in aqueous solution
Authors: Tanodekaew Siriporn , Pannu Rachpal , Heatley Frank , Attwood David , Booth Colin 
Published: April 2003

AbstractDiblock copolymers of ethylene oxide and DL‐lactide (EmLn copolymers) were prepared by sequential anionic polymerisation and characterised by gel permeation chromatography (GPC) and 13C NMR. Their association and surface properties in aqueous solution were studied by surface tension and dynamic and static light scattering. Comparison of the critical micelle concentrations (cmc) and micelle association numbers (Nw) of the EmLn copolymers with published values for oxyethylene/oxybutylene (EmBn) copolymers indicated a slightly lower hydrophobicity for a lactide unit: i.e. L ≃ 0.75B. The temperature dependence of the cmc of copolymer E42L12 was analysed to obtain a standard enthalpy of micellisation ΔmicH0 ≈ 40 kJ · mol−1.
Luminescence quenching of partially quaternized poly(1‐vinylimidazole)‐bound ruthenium(II) complex in methanol
Authors: Suzuki Masahiro , Mori Yoshiaki , Yokoyama Naoki , Kimura Mutsumi , Hanabusa Kenji , Shirai Hirofusa 
Published: April 2003

AbstractMetallopolymers in which bis(2,2′‐bipyridine)ruthenium(II) complexes are coordinated to imidazolyl residues on partially quaternized poly(1‐vinylimidazole) having different degree of quaternization (RuQPIm) were synthesized. The luminescence quenching of the photoexcited RuQPIms with various alkylviologens having different length of alkyl group was investigated in MeOH. In quenching of RuQPIm with methylviologen (MV2+), the efficiency of quenching decreases with increasing degree of quaternization. This was attributed to the electrostatic repulsion between the MV2+ species and the quaternized imidazolium residue on the polymer backbone and steric hindrance of the alkyl side chain. Furthermore, the efficiency of quenching depends on the length of the alkyl group in viologen. These results suggest that the alkyl side chain on the polymer backbone exerts steric hindrance at low degree of quaternization and van der waals interaction at high degree of quaternization.
The crystal structure and drawing‐induced polymorphism in poly(aryl ether ketone)s, 2. Poly(ether ether ketone ketone), PEEKK
Authors: Wang Shanger , Wang Junzuo , Liu Tianxi , Mo Zhishen , Zhang Hongfang , Yang Decai , Wu Zhongwen 
Published: April 2003

AbstractThe crystal structure, morphology and polymorphism induced by uniaxial drawing of poly(ether ether ketone ketone) [PEEKK] have been studied by transmission electron microscopy (TEM), electron diffraction (ED) and wide angle X‐ray diffraction (WAXD). On the basis of WAXD and ED patterns, the crystal structure of unoriented PEEKK is determined to have two‐chain orthorhombic packing with unit cell parameters of a = 0.772 nm, b = 0.600 nm, c = 1.004 nm (form I). A stress‐induced crystal modification (form II) is identified and found to possess a two‐chain orthorhombic lattice with unit cell dimensions of a = 0.461 nm, b = 1.074 nm, c = 1.080 nm. The 7.5% increase in c‐axis dimension for form II is attributed to an overextended chain conformation, arising from extensional deformation during uniaxial drawing and fixed “in‐situ” through strain‐induced crystallization. The average ether‐ketone bridge bond angles in form II crystal are determined to be 148.9° by using standard bond lengths. The crystal morphology of PEEKK bears a great similarity to that of PEEK. The crystals grow in the form of spherulites and have the b‐axis of unit cell radial. The effects of draw rate on strain‐induced crystallization and induction of form II structure are also discussed.
Biodegradable drug carriers based on poly(ethylene glycol) block copolymers
Authors: Pechar Michal , Strohalm Jiří , Ulbrich Karel , Schacht Etienne 
Published: April 2003

AbstractThe synthesis of a model water‐soluble drug carrier system based on poly(ethylene glycol) (PEG) block copolymers is described. In the system, two blocks of PEG are connected via a biodegradable oligopeptide or amino acid linkage incorporating at least one glutamic acid residue. A drug model (4‐nitroaniline) is attached to the γ‐carboxyl group of glutamic acid of the polymer carrier via an enzymatically degradable oligopeptide spacer. All oligopeptides were prepared as potential substrates for cathepsin B, a representative of lysosomal enzymes. The relationship between the structure of oligopeptides forming the linkage between two PEG molecules and the rate of cathepsin B‐catalyzed polymer chain degradation is evaluated. The relationship between the structure of the spacer and kinetics of drug model release from the carrier after incubation in cathepsin B solution is also discussed in detail. The results show that, by altering the structure of oligopeptides in the polymer construct, marked changes in the rate of both polymer degradation and the drug model release can be achieved.