bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of γ‐irradiation on the electrical properties of cellulose nitrate
Authors: Amin M. , Mounir M. , Darwish K. A. 
Published: April 2003

AbstractTwo types of cellulose nitrate were studied; the red cellulose nitrate LR‐115 type 2 and the light pink CA 80–15 samples (Kodak, France). The samples were exposed to different doses of γ‐rays from a 60Co‐source (from 0.1 – 0.3 Mrad) at room temperature. Conductivity and dielectric constant measurements were carried out. For both nitrate samples (CA 80–15, LR‐115), the electrical conductivities are high in comparison with the unirradiated ones for a dose of 0.1 Mrad, but there is a slight change between 0.1 and 0.2 Mrad doses for CA 80–15 samples while the electrical conductivity is found to be less for 0.3 Mrad due to the damage in the plastic network. Also for the samples LR‐115 the electrical conductivity is lower for doses of 0.2, 0.3 Mrad than that for 0.1 Mrad dose. We notice that the glass transition temperature (Tg) of cellulose nitrate is clearly affected by γ‐irradiation as judged from the anomalies in σ(T) for the two samples which contain different amounts of the pigment. Irradiation of LR‐115 samples resulted in a higher dielectric constant for 0.1 Mrad dose and a lower one for 0.2, 0.3 Mrad doses, but still higher relative to the fresh sample. The dielectric constant of irradiated CA 80–15 samples (0.1, 0.2 Mrad) is found to be high relative to the fresh sample, but for 0.3 Mrad dose the dielectric constant is lower than that of the fresh one.
Immobilization of trypsin on poly(alginic acid‐g‐glycidyl methacrylate‐co‐hydroxy ethyl methacrylate)
Authors: Reddy C. Raghuram , George Anne , Reddy C. Rami 
Published: April 2003

AbstractTo synthesize a matrix for the immobilization of enzymes, alginic acid, a naturally occurring polysaccharide has been chosen as the backbone, and glycidyl methacrylate (GMA) and 2‐hydroxy ethyl methacrylate (HEMA) as monomers for graft copolymerization. HEMA was used to introduce hydrophilic character which would have been lost during the introduction of the hydrophobic monomer glycidyl methacrylate into alginic acid. Immobilization of trypsin onto this matrix takes place by covalent bonding. The temperature optimum of the immobilized enzyme was found to be 35°C and it was most stable at pH 8.
The diels‐alder reaction and copolymerization of halogenated N‐phenylmaleimides with dienes
Authors: Lokaj Jan , Pivcová Hana , Hrabák František 
Published: April 2003

AbstractThe course of the Diels‐Alder reaction of N‐(2,4,6‐tri‐bromophenyl)maleimide (I) with 2‐methyl‐1,3‐butadiene (Ip) and of N‐(2,4,6‐trichlorophenyl)maleimide (II) with Ip, 2‐chloro‐1,3‐butadiene (Cp), and butadiene (Bt) in CHCl3 was investigated. For the I‐Ip addition, the reaction order was determined with respect to both components, and the activation energy was calculated. The Diels‐Alder adducts thus obtained were characterized by elementary analysis, by 1H‐ and 13C‐NMR spectra, specific volume contractions, melting points, solubilities, and polymerization abilities. Copolymers of I and II with Ip, Cp, Bt, and 2‐methylpropene (Ib) were prepared, and their composition was determined. The copolymerization and Diels‐Alder addition of I‐Ip and II‐Ip occurring in parallel were investigated, and the participation of these two processes in the total reaction was discussed.
Polymerization characteristics of a dye of anthraquinone
Authors: Hrabák František , Lokaj Jan , Tkaczyk Martin , Morozova Elena , Eliseeva Valentina , Chuiko Leonid , Voloshin Gennadii 
Published: April 2003

AbstractA technical dye of the anthraquinone type was analyzed by GPC, mass spectroscopy, and elemental analysis. Along with the polymerizable component, N‐[4‐amino‐3‐methoxyanthraquinonyl‐(1)] methacrylamide (I), it contained a saturated admixture, N‐[4‐amino‐3‐methoxyanthraquinonyl‐(1)]‐2‐chloro‐2‐methylpropionamide (II). The homopolymerization of I was carried out, and admixture II was isolated and characterized. The copolymerization of the dye with styrene and methyl methacrylate was verified, and the retardation effect of II on the polymerization of these monomers was evaluated.
On the inclusion copolymerization of some vinyl and diene monomers in different types of matrices
Authors: Schneider Ch. , Greve H. H. , Bohlmann H. P. , Rehbold B. 
Published: April 2003

AbstractThe inclusion copolymerization of various vinyl monomer systems was studied in a thiourea and perhydrotriphenylene matrix while that of a disubstituted butadiene system was investigated in canals of thiourea, perhydrotriphenylene, deoxycholic acid and β‐cyclodextrine. The results were compared with those obtained for the corresponding free copolymerization especially with regard to copolymer composition. In all vinyl monomer systems inclusion copolymerization leads to the same copolymer composition as is found in the free process. On the other hand, in case of the diene system, the copolymer composition of the inclusion products is remarkably different from that of the copolymers formed by the free reaction; the former is always nearly ideal statistic independent of the nature of the host. Inclusion homopolymerization can successfully be carried out with monomers where the free radical polymerization is prevented by allylic inhibition.
Alternierende copolymere über komplexierte monomere
Authors: Eisenbach C. D. , Bülow U. , Daum U. , Fürderer B. , Schmidt F. G. , Fischer H. , Ulmschneider D. 
Published: April 2003

AbstractDie unter präparativen Aspekten wichtigste Erkenntnis der Untersu‐chungen ist, daß die Copolymerisation ürber komplexierte Monomere iiber den gesamten Verlauf kontrolliert werden kann, und nicht– wie in der Literatur beschrieben – spontan einsetzt; von grundsltzlich‐ er Bedeutung ist der totale Ausschluß van Oxidationsmitteln (Sauer‐stoff, organische Peroxide) im System bevor die Polymerisation ge‐startet wird. Die Polyreaktion weist viele Merkmale der klassischen, nach einem Radikalkettenmechanismus ablaufenden Polymerisation auf, und sowohl Umsatz als auch Molgewichte köronnen durch entsprechende Wahl der Reaktionskomponenten und –bedingungen iiber einen weiten Bereich kontrolliert werden; zu einem umfassenden Verständnis der Elementarschritte der Polyreaktion sind jedoch noch weitere Unter‐suchungen erforderlich. Was die Eigenschaften der alternierenden Co‐polymeren anbelangt, so hat die Charakterisierung der synthetisier‐ten Polymeren gezeigt, daß das Eigenschaftsprofil deutlich von dem statistischer Copolymerer abweicht.Die Autoren danken dem Bundesministerium für Forschung und Technologie für diefinanzielle UnterstCitzung dieser Arbeiten. Den Herren Prof. Dr. H. Cherdron und Dr. L.L. Boöhm danken wir fürr wertvolle Hinweise und Diskussionen.
Giessfolien mit kristallinen TCNQ‐radikalionensalzen: Ein neuer weg zur erhöhung der elektrischen leitfähigkeit
Authors: Hocker Jürgen , Jonas Friedrich , Müller Hans‐Klaus 
Published: April 2003

AbstractThe electrical conductivity of conventional polymers like, for example, polycarbonate can be increased many magnitudes by adding suitable radical ion salts based on tetracyanoquinodimethane. The formation of suitable crystal structures like dendrites, fibrous crystals and whiskers plays a vital rôle in this: the crystalline precipitation must form a three‐dimensional network throughout the entire polymer matrix, and can only be produced by crystallization from solution. Given an ideal distribution of crystals in the films, additions of approx. 0.5 % by weight will give conductivities of up to 10−3 S/cm. Unlike conventional anti‐static agents (hydrophilizing agents), crystalline radical ion salts give films electrically conductive properties which are practically independent of atmospheric humidity. The films behave like electrical semiconductors and have a positive temperature gradient. In view of the small amount of additive required, these modified polycarbonate films can be used as transparent packaging films whose anti‐static properties are unaffected by atmospheric moisture.
The construction of new proteins
Authors: Mutter Manfred , Altmann Karl‐Heinz 
Published: April 2003

AbstractRecent progresses in the elucidation of the folding mechanism and topology of proteins revealed that the formation of folding units with specific topological features is not restricted to a unique primary sequence. This finding presents the basis for the design of polypeptides having the propensity to fold into a tertiary structure that can be achieved by the assembly of peptide blocks exhibiting stable secondary structures. Conformational studies on model peptides show that Aib containing peptides with chain‐lengths of 12‐15 residues are able to form stable amphiphilic helices in solution. On the other hand, oligopeptides with alternating hydrophilic and hydrophobic residues are capable for β‐structure formation for chain‐lengths of 6‐8 residues. Those amphiphilic secondary structures have been used as building‐blocks for the design and synthesis of artificial folding units, their amphiphilic nature acting as major driving force for intramolecular folding. Spectroscopic data obtained for two polypeptides designed as βαβ‐models actually suggest a folded conformation of these molecules in aqueous solution. The implications of these findings for the design of biologically active folded polypeptides are discussed.
Thermotropic liquid crystalline polymers
Authors: Wendorff Joachim H. , Zimmermann Hans J. 
Published: April 2003

AbstractRigid chain molecules have the tendency to display fluid liquid crystalline phases within a limited temperature range. This range depends on the particular chemical structure of the chain molecules. The chain rigidity as well as the intrinsic dynamical and elastic properties of the liquid crystalline melt can successfully be used to obtain high strength, high stiffness polymers, which can be melt processed. The rigid chain polymers display unusual thermodynamical, dynamical, structural, rheological and mechanical properties.
Polymere hochleistungs‐faserverbundwerkstoffe
Authors: Lang R. W. , Stutz H. , Heym M. , Nissen D. 
Published: April 2003

AbstractAdvanced polymer‐matrix composites are defined as materials consisting of continuous high strength, high modulus fibers, aligned and embedded in a polymeric matrix. Due to their low density they exhibit specific mechanical properties (i.e., strength/density and stiffness/density) that considerably exceed those of high strength metals, which demonstrates their great potential for lightweight structural components. The primary reinforcement materials are various types of carbon fibers, aramid fibers and glass fibers. While these are commonly combined with epoxy resins, many new matrix systems with distinct property profiles, including heat resistant thermoplastics, have been developed recently. This paper presents an overview of this rapidly developing field covering principles of composite‐property improvement, synthesis and processing of the constituent materials, and processing and manufacturing techniques to combine fibers and matrix to produce a composite laminate or part. Several mechanical composite properties critical for structural design and performance are discussed in terms of the contribution of and interaction between the fiber and matrix constituent.
High performance thermoplastics
Authors: Hergenrother Paul M. 
Published: April 2003

AbstractThermoplastics are currently receiving considerable attention for potential use as structural resins in aerospace vehicles. These materials offer an attractive combination of chemical, physical and mechanical properties. Perhaps the most important advantage offered by the thermoplastics over the new toughened thermosets in composite applications is the potential of low cost manufacturing. However, many problems must be resolved with the thermoplastics before they find extensive use in aerospace composite applications. As part of an effort on improved thermoplastics for use as structural resins, NASA Langley Research Center has been intimately involved in research on polyimides, polyarylene ethers, and polyphenylquinoxalines. Several new semi‐crystalline polyimides with high adhesive properties [e.g. Ti/Ti tensile shear strength @ 25°C of 54.1 MPa] and high fracture energies (GIc) [e.g. 6600 J/M2] are under evaluation. New polyarylene ethers offer glass transition temperatures ranging from 114 to 280°C, crystalline melt temperatures of 275 to 400°C, fracture energies (GIc) as high as 6300 J/M2, and good processability. Ethynyl groups were placed on the ends of arylene ether oligomers and subsequently cured to provide materials with excellent adhesive properties and solvent resistance. In the polyphenyl‐quinoxaline family, various new homo, co and crosslink polymers display improved processability, good mechanical properties, and higher use temperature. The chemistry (structure/property relationships), mechanical and physical properties of these new thermoplastics are discussed herein.
Chain‐extended flexible polymers
Authors: Lemstra P. J. , Bastiaansen C. W. M. , Meijer H. E. H. 
Published: April 2003

AbstractHigh‐strength/high‐modulus structures such as fibres, tapes and rods can be produced currently on the basis of intrinsically flexible macromolecules. The prime example amongst these new developments is gelspinning of high‐molecular‐weight polyethylene resulting in fibrous structures possessing tenacities of 3–4 GPa and corresponding moduli up to appr. 150 GPa. The basic aspects of chain‐extension for polyethylene will be discussed in relation to the various routes toward oriented/extended PE structures as well as recent developments concerning the utilization of other flexible polymeric systems for the production of high‐strength/high‐modulus fibres.
Polymere als substrate für optische plattenspeicher
Authors: Hennig Jürgen 
Published: April 2003

AbstractAt the moment PMMA and PC are generally used as substrates for ROM optical discs. In several cases inorganic glass is preferred for DRAW and E‐DRAW information carriers especially because of its high‐barrier characteristics. The benefit of PMMA having low sensitivity to orientation birefringence is opposed by the disadvantage of high water absorption causing warp. It is just the inverse situation with PC. So a polymer material would be desirable which exhibits low optical anisotropy and simultaneously reduced water absorption. The anisotropy problem could possibly be solved regarding additivity of bond polarizabilities within the monomer units, i. e. compensating positive and negative anisotropies by copolymerisation or blending. Reduced water absorption means avoiding polar groups. Polymers are scarcely real barriers against O2 and H2O vapor compared to metals and inorganic glass. PAN and PVDC could be relatively effective as thin layers.
Unvernetzte epoxid‐amin‐additionspolymere, 16. HPLC‐analyse und 13C‐NMR‐spektroskopie von telechelen (diglycidylether‐bisphenol A)‐anilin‐prepolymeren
Authors: Klee Joachim , Hörhold Hans‐Heinrich , Tänzer Wolfram , Fedtke Manfred 
Published: April 2003

AbstractEs wird über die Herstellung von telechelen Diglycidylether‐Bisphenol A (DGEBA)‐Anilin‐Prepolymeren mit sekundären Aminoendgruppen und ihre Eigenschaften berichtet. Mittels HPLC an LiChrosorb RP‐18 wird die Zusammensetzung der im Zuge der Oligoaddition entstandenen Prepolymermischungen analysiert und ihre chemische Struktur durch C, H, N‐Analysen, M̄n‐Werte (Dampfdruckosmometrie, VPO) und 13C‐NMR‐Spektren belegt.
Influence of synthesis conditions of porous copolymers of 1,4‐DI(methacryloyloxymethyl) naphthalene with divinylbenzene on their structure, 1. Influence of mol composition of monomers
Authors: Matynia T. , Gawdzik B. 
Published: April 2003

AbstractPorous sorbents for gas chromatography obtained by the copolymerization of two crosslinking agents (1,4‐di(methacryloyloxymethyl)naphthalene and divinylbenzene) in the presence of a two‐component diluent were studied. In order to establish the influence of synthesis conditions on their internal structure, surface areas, pore size distributions, pore volumes as well as polarity of packings were investigated. The influence of 1,4‐di(methacryloyloxymethyl)naphthalene concentration on the surface area was determined for the polymer obtained in the presence of a constant volume ratio of diluents to monomers. The influence of volume ratio of diluents to monomers on pore volume was studied for three series of polymers containing mole fractions of the polar monomer for 0.2, 0.5, and 0.8.
Study of CU(II)‐methacrylic acid — methacrylamide copolymer interactions and formation of metal‐copolymer complexes
Authors: Chatterjee S. K. , Gupta S. , Sethi K. R. 
Published: April 2003

AbstractThe methacrylic acid‐methacrylamide copolymer has been synthesized and characterized by known methods. The interaction of the copolymer with a typical transition metal ion (e.g. Cu2+) has been studied by several experimental techniques, e.g. viscometry, potentiometry, conductometry, IR, and UV spectrophotometry. Formation of metal‐copolymer complexes of distinct stoichiometries have been predicted, and some schemes of complexation have been suggested to explain the mode of interaction between the components.
Graft copolymerization of methyl methacrylate onto jute fibers. Studies on vanadium (V)‐cyclohexanol redox system
Authors: Mohanty A. K. , Singh B. C. , Misra M. 
Published: April 2003

AbstractGraft copolymerization of methyl methacrylate (MMA) onto natural jute (chemically modified) was studied using V5+ ‐cyclohexanol redox initiator system. The effects of time, concentration of metal ion (V5+), monomer (MMA), substrate, amount of jute fibers, temperature, and acid concentration on graft yield have been studied. The effects of some organic solvents and inorganic salts on graft yield have also been studied. A grafting mechanism is proposed and an expression has been derived for the reaction rate. Grafting has improved the thermal stability and the light fastness of jute fibers dyed with basic dyes. IR spectra of the natural jute (chemically modified) and grafted jute have been taken. More than 170% graft yield could be achieved with the present system.
Enantioface differentiation by using soluble chiral polymers having 2,3‐exo‐bornanediol groups
Authors: Liu Jui‐Hsiang 
Published: April 2003

AbstractSoluble linear polymers containing 2,3‐exo‐dihydroxy‐3‐endo‐p‐tolyl‐3‐bornyl groups prepared by reaction of lithiated linear polystyrenes with (‐)‐2‐exo‐hydroxy‐3‐bornanone, are treated with lithium aluminium hydride to form complexes which can be used as reducing reagents. The highest enantioselectivity compared with those cases using crosslinked polystyrene as carrier and chiral low molecular weight compounds is achieved by linear polystyrene having chiral groups. The advantages of soluble polymer‐bound chiral reagents are discussed. The effect of alcohols, the reaction temperature, the sort of solvents, and the molar ratio of the reagent to ketone on the asymmetric reduction is also discussed.
Graft copolymerization of unsaturated segmented polyurethanes with 2‐hydroxyethyl methacrylate
Authors: Egboh Sunday H. O. 
Published: April 2003

AbstractRelatively high molecular weight unsaturated segmented polyurethane synthesized from poly(ethylene glycol), methylene bis(4‐phenyl isocyanate), cis‐2‐butene‐1,4‐diol, and butane‐1,4‐diol was modified by graft copolymerization reaction. 2‐Hydroxyethyl methacrylate (HEMA) monomer was grafted onto the unsaturated segmented polyurethane using 2,2′‐azobisisobutyronitrile (AIBN) as initiator in N,N‐dimethylformamide (DMF) as solvent. The graft copolymers were isolated by selective solvent extraction in a Soxhlet apparatus. The effect of reaction time, initiator concentration, reaction temperature, and monomer concentration on the graft yields has been examined. The graft yields were enhanced by increased monomer concentration and reaction temperature.
Effect of pressing on the diffusional properties of polyacetylene
Authors: Chen Show‐An , Chan Wu‐Chung , Li Liang‐Shun 
Published: April 2003

AbstractPressing of polyacetylene films before (or after) sorption of dopant can reduce significantly the rate of sorption (or desorption) due to reduced effective surface area and pore size, as is found in the experiments of vapour sorption and desorption of hexane and iodine. On exposure to air, the pressed films have significantly lower oxidation rates at 120°C than the unpressed ones.
Effect of copolymers modifying PVC on its physical and mechanical properties and its UV‐radiation resistance. VIII. Thermal and photochemical stability of PVC films containing polystyrene and their permeability
Authors: Kamińska A. , Kaczmarek H. 
Published: April 2003

AbstractThe influence of a polystyrene (PS) content of 1–5% in PVC films on their thermal stability, permeability of air and photooxidation, crosslinking, and photodehydrochlorination induced by 253.7 nm wavelength radiation was investigated.It was found that a small amount of PS in PVC films causes an increase of the permeability of air through these films and does not affect their thermal stability, but evidently improves their photochemical resistance hampering the photodehydrochlorination, crosslinking and photooxidation of PVC.These degradation processes change the thermal stability of the samples. Smaller changes observed in samples containing PS confirm its photostabilizing effect on PVC. Visible differences between the values of thermal parameters depending on the efficiency of photochemical reaction point out the sensitivity of derivatographic measurements on conversion of PVC caused by UV‐radiation.
Miscibility of chlorinated polymers with epoxidized natural rubber II. Blends with chlorinated polypropylene and with poly(vinylidene chloride‐alkyl acrylate) copolymer
Authors: Kallitsis John K. , Kalfoglou Nikos K. 
Published: April 2003

AbstractThe compatibility of epoxidized natural rubber (at the 50 mol‐% oxirane level) (ENR) with chlorinated polypropylene (CPP) and a poly(vinylidene chloride) copolymer (PVDCC) was investigated in the complete composition range. Phase‐contrast microscopy revealed microheterogeneities attributed to the existence of gel particles in the solution‐cast films. A more uniform phase distribution was obtained in hotpressed films.Dynamic mechanical spectroscopy and DSC results indicated that both systems are miscible at the segmental level. Ultimate elongation increases at significant (>50 wt.‐%) ENR levels.The blend modulus dependence on composition supports the view that synergistic effects are present. These can be explained by postulating the existence of intermolecular interactions predicted using suitable models proposed to interpret the compositional variation of Tg.
Syntheses and characterization of polycondensation products derived from ß‐(4‐ethoxyphenyl)glutaconic acid and diols
Authors: Patel Nita R. , Patel Rajni M. 
Published: April 2003

AbstractUnsaturated polyesters (3a—f) were prepared by condensing ß‐(4‐ethoxyphenyl)‐glutaconic acid (1a) with various diols (2a—f). The polycondensates were characterized by IR, TG, DSC, VPO, and elemental analysis. All polymers were found to decompose in the range of ∼200° to ∼600°C. The kinetic parameters and the stability of the resins are reported.
Synthesis and characterization of resorcinol‐cinnamaldehyde resins
Authors: Žigon Majda , Šebenik Anton , Osredkar Uči , Vizovišek Ivan 
Published: April 2003

AbstractThe mechanisms and kinetics of the reaction between resorcinol and cinnamaldehyde were studied by means of 13C‐NMR spectroscopy, HPLC, and GPC. In the first step the addition of resorcinol to the double bond and to the carbonyl group of cinnamaldehyde takes place. In the second step of reaction the lower molecular weight oligomers form compounds with groups with molecular weights between 1500 and 2500. The red coloured resin reacts at temperatures above 150°C with crosslinking agents to form an insoluble and highly crosslinked product.