bluuebunny/crossref_metadata_2025_split huggingface dataset:
A theoretical study of conformations and electronic band structures for two benzoxazole polymers
Authors: Nayak Kasinath , Mark James E. 
Published: April 2003

AbstractThe extended Hückel method within the tight‐binding approximation was applied to two benzoxazole polymers of a type much studied because of their excellent mechanical properties. Specifically, band structure calculations were carried out in part to identify the most stable conformation of the polymers in the crystalline state. In the preferred conformation of one polymer the rotational angle between the bibenzoxazole groups is 20°, and that between the bibenzoxazole group and the p‐phenylene group is 0°. The other polymer consists simply of benzoxazole groups, and these are predicted to be coplanar. The above conformational predictions are in excellent agreement with the results of both experimental and theoretical studies on relevant model compounds. In addition, the band gaps in the axial direction were found to be 1,86 and 2,31 eV, respectively, and these values are close to the corresponding experimental values 1,4 to 1,8 eV reported for trans‐polyacetylene. In both benzoxazole polymers the band gap was found to increase with increase in nonplanarity due to the concomitant reduction in charge delocalization.
Morphology, crystallization and thermal behaviour of poly(ethylene oxide)/poly(vinyl acetate) blends
Authors: Martuscelli Ezio , Silvestre Clara , Gismondi Carla 
Published: April 2003

AbstractBlends of poly(ethylene oxide) (PEO) and poly(vinyl acetate) (PVAc) show a unique value of the glass transition temperature, intermediate between that of plain polymers. The addition of PVAc to PEO causes a depression in both the spherulite growth rate (G) and the overall kinetic rate constant (Kn). Such depression is larger at higher undercooling and, at a given crystallization temperature, it increases with the content of PVAc. The experimental G and Kn data were analyzed by means of latest kinetic theories in order to determine the influence of composition on the process of surface secondary nucleation. The melt behaviour of PEO/PVAc blends cannot be explained only in terms of diluent effects due to the compatibility of the components in the melt. Especially, at lower undercooling it is likely that annealing and morphological effects must also be taken into account. The morphology of thin films of blends, isothermally crystallized from melt, suggests that an amorphous mixed phase (PEO + PVAc) is formed in interlamellar regions. It was found that plain PEO crystals grow according to a regime I process of surface secondary nucleation while in the case of blends the crystals of PEO grow via regime II mechanism.
Polymeric phthalocyanines and their precursors, 7. Synthesis and analytical characterization of polymers from 1,2,4,5‐benzenetetracarboxylic acid derivatives
Authors: Wöhrle Dieter , Preußner Elke 
Published: April 2003

AbstractStructurally uniform polymeric phthalocyanines 5a–e, containing imido end groups, were synthesized by reaction of different derivatives of 1,2,4,5‐benzenetetracarboxylic acid, 2a–d, with metal salts, urea and a catalyst. 5a–e were converted into polymers 3, 4 and 6, containing anhydride, carboxylic acid and amido end groups, respectively. IR and UV/VIS spectroscopy were used as appropriate methods for describing end groups and structural uniformity. It could be shown that the octasubstituted phthalocyanines 7–10 and not the phthalocyanine 1 must be considered as the low‐molecular‐weight analogues. The number of phthalocyanine units in the polymers was found to be ⩾ 9. The determination of the real molecular weights is not possible, due to the low solubility of the polymers.
Blockcopolymere aus 2‐Isopropenylnaphthalin und Hexamethylcyclotrisiloxan, 7
Authors: Rhein Thomas , Schulz Rolf C. 
Published: April 2003

AbstractAnionic polymerization of 2‐isopropenylnaphthalene (2‐IPN), with butyllithium in THF at −78°C was terminated with ethylene oxide and the resulting terminal alkoxide was used to initiate the polymerization of hexamethylcyclotrisiloxane (D3) at +40°C. This led to the formation of AB‐block copolymers which were coupled to ABBA‐block copolymers by addition of dichlorodimethylsilane. ABBA‐blockcopolymers were obtained with contents of polymethylsiloxane (poly(DMS)) between 77 and 84% of weight and block molecular weights between 1 700 and 27 000 (poly(2‐IPN)) and 13 000 and 240 000 (poly(DMS)). Phase separation in polymer films casted from different solvents was studied by electron microscopy and by DSC measurements. The block copolymers behave as elastomers in the temperature range from −40 to +190°C. Above 290°C depolymerization of poly(2‐IPN) starts.
Functional monomers and polymers, 127. Application of polymer‐bound nucleic acid bases to high performance liquid chromatography
Authors: Yu Yan Sheng , Kondo Koichi , Takemoto Kiichi 
Published: April 2003

AbstractNucleic acid bases and their derivatives, such as cytosine, hypoxanthine and guanine, were linked successfully to polyethyleneimine coated silicagel. These resins were found to separate nucleic acid bases, nucleosides, nucleotides and other purine derivatives efficiently in aqueous solution by means of high performance liquid chromatography.
Changes in molecular structure of ultra‐high molecular weight polyethylene hostalen GUR upon ageing of its solutions at elevated temperature
Authors: Quadrat Otakar , Horská Jitka , Stejskal Jaroslav 
Published: April 2003

AbstractChanges in solutions of ultra‐high molecular weight polyethylene Hostalen GUR in 1,2,4‐trichlorobenzene with time were studied by means of viscometry and light scattering. The decrease of viscosity during ageing indicates that both the degradation of polyethylene chains and destroying of aggregates may occur. The former fact makes questionable the ultra‐high molecular weight character of the sample.
Hydrodynamic behaviour of 1,4‐trans‐polyisoprene
Authors: Chaturvedi Prakash N. , Patel Chiman K. 
Published: April 2003

AbstractThe unperturbed dimensions of 1,4‐trans‐polyisoprene (TPIP) were estimated using various [η] – Mw extrapolation methods. The results of various methods agree very closely, however, the solvent‐polymer interaction parameter, B, assumes different values from method to method. The polymer chains are found to assume random coil structure in solvents like benzene, toluene and cyclohexane. A more compact coiled structure is found in hexane. This was further substantiated by estimation of the excluded volume per segment: 7,3 Å3 in good solvents and 4,0 Å3 in hexane. On a relative scale, the stiffness parameters for TPIP chains were found to be: σ = 1,26 and C∞ = 5,99 for the expanded coil configuration, and σ = 1,11 and C∞ = 4,46 for the compact coil configuration, which is smaller than the literature data. If the latter are corrected for molecular heterogeneity, the agreement with the present data is excellent. The temperature coefficient of the unperturbed dimensions also supports this results.
Complexes of polyelectrolytes with the enzymes pepsin and α‐chymotrypsin
Authors: Lawton John B. , Mekras Christos I. 
Published: April 2003

AbstractIt was shown that both the enzymes pepsin and α‐chymotrypsin will displace the anionic dye Eosin Y from complexes of the dye with the polycations protamine or polybrene. The dyerelease was monitored fluorimetrically and was found to be strongly time‐dependent. At equilibrium, pepsin released all the bound dye from both polycation‐dye complexes when the mole ratio of pepsin to base moles of polycation were 1 : 10 for protamine and 1 : 13 for polybrene. α‐Chymotrypsin did not release all the bound dye, but appeared to form definite complexes with the polycations. The existence of the complexes between the enzymes and the polycations was correlated with the fact that the polycations are inhibitors of the enzymes. Additionally, it has been shown that pepsin releases Acridine Orange (AO) from a poly(vinyl sulfate) (PVS)‐AO complex. The mole ratio of pepsin to base moles of PVS was found to be 1 : 2,5. Cooperative binding constants were also evaluated for each dye‐polyion system.
Synthesis of a new chelate resin for uranium adsorption from seawater. Polystyrene resin containing two amide oxime functions in the repeating unit
Authors: Kise Hideo , Sato Hisayuki 
Published: April 2003

AbstractDicyanoethylated polystyrene, poly{1‐[4‐(2,2‐dicyanoethyl)phenyl]ethylene} (2), which was obtained from the reaction of chloromethylated polystyrene, poly[1‐(4‐chloromethylphenyl)‐ethylene] (1) with malononitrile under phase transfer reaction conditions, was treated with hydroxylamine in methanol to afford a polystyrene resin 3 with two amide oxime functions in the repeating unit. Resins 3 exhibit a higher adsorptivity of uranium in seawater than a corresponding resin 5 with one amide oxime function in the repeating unit. The effective adsorption of uranyl ions by resins 3 is attributed to the close proximity of the two amide oxime functions in the styrene monomeric unit, which can effectively coordinate to a uranyl ion.
N‐substituted methacrylamide copolymers. Novel membranous material for carbon kidney
Authors: Li Xue‐fen , Wang Shen‐guo , Li Zhi‐fen , Gu Han‐qing , Xu Shu‐tao , Liu Xiao‐bing , Zhang He‐shun , Yu Sung‐ting , Ma Teng‐xiang 
Published: April 2003

AbstractCopolymers of N‐substituted methacrylamide (1a, b), new biomaterials, were synthesized to be used as encapsulating membranes of carbon kidney. In order to obtain a copolymer with a suitable hydrophilic property, the aminolysis of styrene‐methyl methacrylate (St‐MMA) copolymer with N‐(2‐hydroxyethyl)ethylenediamine was carried out under various conditions. The occurrence of aminolysis was confirmed by elemental analysis, IR and 1H NMR spectra. It was shown that a copolymer of N‐substituted methacrylamide with a predictable degree of hydrophilicity can be obtained by controlling the composition ratio of the St‐MMA copolymer and the degree of aminolysis of the copolymer. Hemoperfusion experiments with a living animal (dog), using a minicolumn with several types of microspheric activated carbon encapsulated with various copolymers, showed that copolymers with suitable hydrophilicity and hydrophobicity or with proper structure have a good blood compatibility. Studies with creatinine, uric acid and vitamin B12 showed that microspheric activated carbon, encapsulated with N‐substituted methacrylamide copolymers of proper hydrophilicity and structure, has a good penetration property, and that detaching of activated carbon particles is effectively prevented.
Thermal analysis of the phase transitions of poly(p‐xylylene)
Authors: Kirkpatrick Donald E. , Wunderlich Bernhard 
Published: April 2003

AbstractDifferential scanning calorimetry is used to analyze the phase transitions of various heat‐treated poly(p‐xylylene)s, polymerized from 78 to 296 K. The data were extrapolated, as needed, to completely amorphous or completely crystalline polymer. The glass transition was found to be at 286 K; the increase in heat capacity at the glass transition is 37,6 J · K−1 · mol−1. The crystals of the α polymorph change at 504 K to the β1 polymorph (enthalpy of transition of 5,0 kJ · mol−1), then, at 560 K to the β2 polymorph (enthalpy of transition of 1,5 kJ · mol−1), and finally at 700 K to the isotropic melt (heat of transition of 10,0 kJ · mol−1). Both the β1 and β2 polymorphs are assumed to be conformationally disordered (condis crystals). The reversibility of the transitions, annealing peaks, crystallization on heating, abnormally high heat capacities of β1 crystals, and abnormally low heat capacities of α crystals are discussed.
The structure and time evolution of a cellulose sheet in the nascent fibril produced by acetobacter xylinum
Authors: Kai Akira , Koseki Tomoki 
Published: April 2003

AbstractStructure and time evolution of a nascent cellulose sheet, produced by Acetobacter xylinum, were examined regarding the resistance of the nascent fibrils to alkali. It became clear that the never‐air‐dried cellulose, obtained after an incubation period of 5 min, changes its morphology after an alkali treatment at very low concentrations (ranging from 1,0 · 10−3 to 1,0 · 10−2 wt.‐%). It is subsequently transformed into cellulose II. On the other hand, although the fibril after an incubation period of 30 min seems to be in a stainable state toward sodium tungstophosphate when it was treated with 4,6 wt.‐% alkali, 70–80% of it maintains the fibrous shape. Electron diffraction experiments, involving the fibrils, indicate a cellulose I structure. Even when the sample after an incubation period of 30 min was treated with 9,6 wt.‐% alkali, about 30% of it still maintains the fibrous shape. Electron diffraction experiments, involving the fibrils, also indicate a cellulose I structure. The shape of a cellulose sheet, just after its extrusion from a cell, seems to be maintained by hydrophobic bonds. The enhancement of the resistance of cellulose toward alkali with time must be due to the development of inter‐and intramolecular hydrogen bonds in each cellulose sheet.
Modified affine law for the elastic and optical properties of low density polyethylene
Authors: Biswas Prabir K. , Sengupta Shyamal , Basu Asok N. 
Published: April 2003

AbstractA unified study of the anomalous mechanical properties and birefringence of low density polyethylene (LDPE) is attempted within the frame work of the rotating element model. The present paper investigates the validity of the affine transformation rule used in the Ward model and suggests a modified affine law which is based on the consideration that the units are only reoriented and, unlike the affine law, are not deformed due to the uniaxial stretching. The relationship between the angles made by the C‐axis of the unit with the drawing direction in the undrawn state (θ) and the drawn state (θ), is deduced as sin θ = f(n) sin θ′. From the birefringence data of different polymers a two parameter relation of the form f (n) = exp [–(n – 1)α/β] is suggested. Using this new orientation function, the agreement of the predicted values of E0 and E90 for LDPE for the entire draw ratio range between temperatures of 60°C to −125°C, is quite satisfactory. An interesting feature is that the abrupt change in the values of the parameters α and β at two different temperatures may be associated with a phase transition of LDPE at an intermediate temperature.
Comparison of the cationic polymerization of octamethylcyclotetrasiloxane and hexamethylcyclotrisiloxane
Authors: Wilczek Lech , Rubinsztajn Stawomir , Chojnowski Julian 
Published: April 2003

AbstractSome features of the cationic polymerization of hexamethylcyclotrisiloxane (D3) and octamethylcyclotetrasiloxane (D4) in methylene chloride in the presence of a strong protonic acid (CF3SO3H) were compared. The polymerizations of both these monomers show many similarities, which are taken as evidence for analogies in their mechanisms. In particular, in both cases the reaction is affected by the addition of a small amount of water. The role of water is interpreted in terms of its direct participation in some elementary reactions of the process. The addition of water affects also the state of hydrogen bonding association in the system. Some experimental results together with comments concerning the mechanism of ring formation in the polymerization system are included.
Axially chiral catalysts for the preparation of optically active poly(triphenylmethyl methacrylate)
Authors: Kanoh Shigeyoshi , Suda Hiroshi , Kawaguchi Naotaka , Motoi Masatoshi 
Published: April 2003

AbstractA variety of axially dissymmetric diphenylylene diamines 1a — 1f were synthesized and evaluated as chiral auxiliaries for the polymerization of triphenylmethyl methacrylate with organolithium compounds such as butyllithium and lithium (±)‐N‐(1‐phenylethyl)anilide in toluene at −78°C. The catalysts containing an optically active biphenylylene derivative of tetramethyl‐ethylenediamine (1e) were found to be particularly useful for the preparation of optically active poly(triphenylmethyl methacrylate) (PTrMA). The catalysts afforded tetrahydrofuran (THF)‐soluble polymers in high yields and the polymers showed large optical rotations arising from a one‐handed helical conformation of a polymer chain. (+)‐ and (‐)‐PTrMAs were obtained by using (S)‐1e and (R)‐1e, respectively. The poly(methyl methacrylate)s derived from these PTrMAs were almost completely isotactic, but showed negligible optical rotations. The other catalysts produced mainly polymers insoluble in organic solvents; the small amounts of THF‐soluble materials showed rather low optical rotations.
Synthesis of a stereoblock poly(methyl methacrylate)
Authors: Doherty Martin A. , Hogen‐Esch Thieo E. 
Published: April 2003

AbstractThe sequential block copolymerization of diphenylmethyl methacrylate (DMA) and trityl methacrylate (TrMA), initiated by diphenyl methyl lithium in THF at ‐78°C followed by hydrolysis and methylation with diazomethane, leads to the formation of an isotacticsyndiotactic stereoblock poly(methylmethacrylate) (PMMA) of narrow molecular weight and block length distribution. Complete conversion of DMA is shown to be essential, since the presence of small quantities of this monomer during the polymerization of TrMA significantly lowers the isotactic content of this block. Polymerization times of at least 12 h were found to be necessary for complete polymerization of the TrMA.
Synthesis of fragments of the terminal inverted repeating units of macronuclear DNA from hypotrichous ciliates
Authors: Schott Herbert , Ruess Heinz 
Published: April 2003

AbstractThe four fragments of the terminal inverted repeating units of macronuclear DNA from hypotrichous ciliates d(A4C4), d(C4A4C4), d(A4C4A4C4) and d(C4A4C4A4C4) were synthesized in preparative amounts (300 mg) by block condensation using the phosphotriester procedure. At first, partially protected nucleosides and mononucleotides were condensed to dimeric blocks using 2,4,6‐triisopropylbenzenesulfonyl chloride and N‐methylimidazole. Longer blocks were synthesized from the dimers using 2,4,6‐triisopropylbenzenesulfonyl chloride and tetrazole. After each condensation the reaction mixture was fractionated using a silica gel column and a step gradient. After synthesis, cleavage of the protecting groups and gelchromatographical separation, d(A4C4) and d(A4C4A4C4) were obtained already as pure substances. On the other hand, having cleaved the protecting groups partially or totally, d(C4A4C4) and d(C4A4C4A4C4) were separated first on QAE‐Sephadex by a salt gradient in 7 M urea. The remaining impurities were removed by preparative reversed phase HPLC. Sequence as well as purity of the DNA fragments were proved by partial enzymatic degradation and two‐dimensional chromatography of the hydrolysates (fingerprint).
Solubility parameter of poly(1,3‐dioxepane)
Authors: Marco Carlos , Bello Antonio , Fatou José G. , Garza Justino 
Published: April 2003

AbstractIntrinsic viscosity measurements and turbidimetric titrations were made on poly(1,3‐dioxepane) in a series of solvents to determine the solubility parameter δ. The Flory‐Huggins interaction parameter was also used for the same purpose. A value of δ = 9,2 cal1/2 · cm−3/2 was obtained and compared with that calculated from empirical methods. The three‐dimensional solubility parameter approach was also applied in order to obtain informations about the effect of chemical structure on the solubility behaviour.
Struktur und eigenschaften der copolymere aus 1,3,5‐trioxan und 1‐chlor‐2,3‐epoxypropan, 3. Tempereffekte bei copolymerkristallen
Authors: Michnev Bontcho , Mateva Rosa 
Published: April 2003

AbstractAnnealing of copolymer crystals from 1,3,5‐trioxane and 1‐chloro‐2,3‐epoxypropane (epichlorohydrin (ECH)) was conducted in a differential calorimeter (DSC) and the changes in enthalpy and entropy as well as the shape of the melting curves were observed. The changes in melting enthalpy and the shape of the melting curves were found to depend characteristically on the content of epichlorohydrin comonomeric units in the copolymers. A model for the changes of the crystal by annealing is suggested.
Propene polymerization on titanium‐magnesium catalysts, 4. ESR study of TI3+ ions
Authors: Sergeev Sergei A. , Poluboyarov Vladimir A. , Zakharov Vladimir A. , Anufrienko Vladimir F. , Bukatov Gennadii D. 
Published: April 2003

AbstractThe role of Ti3+ ions in titanium‐magnesium catalysts of various composition, TiCl4/MgCl2 + AlR3, TiCl4/MgCl2 + Al(i‐Bu)3 + EB, TiCl4/EB/MgCl2 + Al(i‐Bu)3 and TiCl4/EB/MgCl2 + Al(i‐Bu)3 + EB, was studied by means of ESR. The ESR data and the catalytic properties were compared. It could be shown that the introduction of ethyl benzoate (EB) leads to an increase of stereospecificity, to a considerable increase of the portion of Ti3+ ions which can be observed by ESR, to the appearance of several new signals in the ESR spectra and to an increase of the portion of titanium in solution, removed from the solid catalyst during the interaction with the organoaluminium cocatalyst. Titanium ions are found mainly in the particles or surface associates whose Ti3+ ions produce no signals in the ESR spectra, Ti3+ ions observed by ESR are found to be inactive centers of polymerization. The active centers appear to be localized in highly dispersed particles or surface associates of TiCl3, formed on the MgCl2 surface and are not revealed in the ESR spectra. Increasing stereospecificity in the presence of EB is assumed to be caused by deactivation of non‐stereospecific active centers with ethyl benzoate.
Aqueous polymerization of vinyl monomers in the presence of surfactants, 3. System: Acrylamide/poly(butyl acrylate) latex
Authors: Bartoň Jaroslav , Vašková Viera , Juraničová Viera 
Published: April 2003

AbstractThe kinetics of the polymerization of acrylamide initiated by potassium peroxodisulfate in aqueous medium is studied in the presence of poly(butyl acrylate) latex. The rate of acrylamide polymerization increases with the concentration of the latex in the reaction system. The increase is especially pronounced at concentrations of solid latex higher than 100 g per dm3 of polymerization mixture. The activation energy of the acrylamide polymerization in the presence of poly(butyl acrylate) latex is 85,8 kJ · mol−1. This value is substantially higher than the value of 70,7 kJ · mol−1 found for the activation energy of the polymerization of acrylamide in the absence of poly(butyl acrylate) latex. A set of reactions is proposed and the equation describing the simultaneous homopolymerization of acrylamide and grafting of poly(butyl acrylate) latex with acrylamide is derived.
Synthesis and thermotropic properties of new mesogenic diacrylate monomers
Authors: Galli Giancarlo , Laus Michele , Angeloni Annino S. 
Published: April 2003

AbstractA new class of mesogenic α,ω‐alkylene bis[4‐(4‐acryloyloxybenzoyloxy)benzoate]s 1a — 1g were synthesized and studied for their mesophase behaviour. The thermodynamic parameters of the isotropization transition Ti, ΔHi and ΔSi show distinct odd‐even alternations and demonstrate that the thermotropic liquid crystalline properties in homologous series of mesogens can not be a continuous function of the length of the inner spacer segment. It is anticipated that the investigated diacrylates are of value as precursors of thermotropic semiflexible polymers, crosslinking agents for mesomorphic polymer networks and low molecular weight twin model compounds.