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  • 1
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A novel, microporous, hydrophilic polyether urethane-urea (PEUU) vascular graft was compared with expanded PTFE in the canine carotid artery. At implantation times ranging from 4 h to 6 months, all the PEUU grafts were found to be occluded while of the PTFE grafts, only those implanted for 1 week and 6 months were blocked. Histopathological analysis of the explanted grafts and their capsules revealed an on-going inflammatory reaction at the anastomotic sites of the PEUU grafts.
    Additional Material: 3 Ill.
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  • 2
    ISSN: 0935-9648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Additional Material: 5 Ill.
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  • 3
    ISSN: 0935-9648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Additional Material: 4 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 9 (1965), S. 2459-2474 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The anionic heterogeneous polymerization of acrylonitrile in petroleum ether by n-butyllithium was studied under various experimental conditions. The dependence of the molecular weight on the total concentrations of the monomer and initiator was strongly affected by the momentary concentration of monomer in the polymerization mixture and by the order of their addition to it. Two polymerization mechanisms were found to operate simultaneously. When monomer was added to the catalyst solution at low rates, nonterminated “living” polymerization was essentially dominant, as was evident from the linear dependence of DP on [monomer] and 1/[BuLi]. Under such conditions DP was independent of the rate of monomer addition. Chain transfer to monomer was the dominant mechanism at high rates of monomer addition, as was evident from the independence of the degree of polymerization of both monomer and initiator concentrations. At intermediate rates of monomer addition the extent of each of the two mechanisms was appreciable, and DP increased with decreasing the rate of monomer addition. A two-stage propagation step in which the growing carbanion of the C-Li+ ion-pair was solvated by monomer, was suggested to be responsible for the dependence of the polymerization mechanism on the momentary concentration of monomer in the polymerization mixture.
    Additional Material: 3 Ill.
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  • 5
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The homogeneous (in dimethylformamide) and heterogeneous (in petroleum ether) polymerizations of acrylonitrile by methanolic solutions of alkali metal methoxides were compared. In the homogeneous system termination of polymerization was by chain transfer to monomer and degree of polymerization (DP) was constant, while in the heterogeneous system termination was by the acidic hydrogen of the alcohol and DP increased with monomer concentration according to the equation DP = Kp[M]/Kt[ROH]. Decrease in temperature led to increase in molecular weight in the heterogeneous polymerization but not in the homogeneous. The positive counterion influenced the molecular weight only under the heterogeneous conditions; the more electropositive potassium gave smaller molecular weights than the sodium catalyst. Owing to the high dielectric constant of dimethylformamide and its high solvating power, the growing ion pairs — — —C-Li+, — — —C-Na+, and — — —C-K+ in this solvent were fully dissociated and showed their “limiting anionic behavior,” leading to the molecular weights' being constant irrespective of polymerization temperature and alkali metal counterions. Because of the high ionic character of the— — —C-K+ bond, the potassium catalyst shows its “limiting anionic behavior” even under heterogeneous conditions, leading to molecular weights of the same order in both the homogeneous and the heterogeneous systems.
    Additional Material: 8 Tab.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 5 (1961), S. 251-260 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The heterogeneous anionic polymerization of acrylonitrile in petroleum ether by potassium alcoholic alkoxide solutions at low temperature was studied. Alkoxides of the more electropositive metal were more active catalysts, ROK 〉 RONa. Increasing amount of alcohol in the polymerization mixture up to a limit, had an activating effect. Yield of polymer increased with catalyst concentration. The mechanism of the polymerization consists of initiation by direct interaction of alkoxide anion with monomer, with no cocatalyst; this is substantiated by the presence of alkoxyl groups in the polymers and by the existence of steric effects of bulkyl alkoxide groups. Termination is by proton abstraction from alcohol. In accordance with this, the degree of polymerization was found to be independent of catalyst concentration, directly proportional to monomer, and inversely to alcohol concentrations, according to the equation, DP = kp[M]/kt[ROH]. Plot of DP versus monomer and the reciprocal of the alcohol concentrations gave values for kp/kt of about 35. All polymerizations showed an induction period with the following regularities. It increased with increasing concentration of alcohol and with lowering of temperature, and decreased with increasing catalyst and monomer concentrations and was smaller with the more active potassium catalysts. Induction periods seem to originate from the competing side-reaction of cyanoethylation, the initiation step of the polymerization being identical with the first step (RO- addition) in the cyanoethylation reaction. Cyanoethylation products were isolated from polymerization mixtures.
    Additional Material: 2 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 8 (1964), S. 1869-1888 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Graft polymers of acrylonitrile, methacrylonitrile and methyl methacrylate on polyhydroxy polymers such as cellulose and polyvinyl alcohol were prepared by anionic graft polymerization. The alkali alkoxide derivative of the polyhydroxy polymer backbone was used as initiator of polymerization. The graft polymerizations were carried out in liquid ammonia and other inert solvents at low temperature. Grafting was accompanied by considerable homopolymerization caused by chain transfer to monomer and to ammonia. The graft polymers were separated from homopolymers and unreacted polyhydroxy polymers by extraction with suitable solvents. The per cent of the grafted vinyl polymer increased with increase in the monomer and alkoxide concentration. No crosslinking occurred during the anionic graft polymerization, and soluble graft polymers were obtained.
    Additional Material: 6 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 9 (1965), S. 2379-2391 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Acetylenic polyesters containing either residues of 2-butyne-1,4-diol, acetylenedicarboxylic acid, or both of them, were prepared and characterized. Polyesters of 2-butyne-1,4-diol with succinic, adipic, and phthalic acids were obtained as soluble polymers by use of known methods. The polymaleate ester of 2-butyne-1,4-diol was obtained either as a soluble or as an insoluble polymer, depending on the experimental conditions. Relatively high temperature or long reaction periods led to the formation of insoluble polymers. Polyesters of acetylenedicarboxylic acid with diethylene glycol, tetra- and hexamethylene glycols, 2-butene-1,4-diol, and 1,4-cyclohexane dimethanol were prepared by melt polycondensation in bulk. These polyesters were obtained as insoluble, rubbery materials, except those of 2-butene-1,4-diol and 1,4-cyclohexane dimethanol, which were obtained both as linear or as nonlinear polymers. The insolubility of the polyesters of acetylenedicarboxylic acid was due to crosslinking reactions involving the conjugated system —C≡C—C=O. While the melt polycondensations in bulk involving either 2-butyne-1,4-diol or acetylenedicarboxylic acid were entirely controlled reactions, those carried out between acetylenedicarboxylic acid and 2-butyne-1,4-diol were very often associated with highly exothermic decompositions involving carbonization. The decompositions could be eliminated when the melt polycondensation in bulk was preceded by a fore-condensation in solution. Solid, soluble, powdery low polymers (DP = 2-3) having softening temperatures of about 150-175°C. were thus obtained.
    Additional Material: 2 Tab.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 9 (1965), S. 2475-2488 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The heterogeneous polymerization of acrylonitrile in petroleum ether by butyllithium in the presence of Lewis bases was investigated. Molecular weights increased sharply on addition of small amounts of Lewis bases. High, maximal molecular weights were obtained at optimal values of [Lewis base]/[BuLi] = 1-2. Beyond this optimum a sharp decrease of molecular weights was observed. The optimal [Lewis base]/[BuLi] ratio was dependent on the Lewis base used and was specifically related to the structure of the complex Li+ Lewis base. The effectiveness of the Lewis bases in obtaining high molecular weights was as follows: DMF ≫ THF ∼ dioxane 〉 dimethylacetamide. A nonterminated “living” polymerization for which DP was given by DP = Rp/Ri was observed with low rates of monomer addition, whereas chain transfer to monomer occurred with high rates. This behavior was qualitatively the same as that found in the absence of any Lewis base. However, under comparable conditions, higher molecular weights were always obtained in the presence of a Lewis base, except for relatively high ratios of [Lewis base]/[BuLi]. It was suggested that at the optimal ratio of [Lewis base]/[BuLi] and beyond it, all the positive Li+ ions in the polymerization mixture were solvated by the Lewis base. This solvation increased the nucleophilic reactivity of the carbanions. On increasing the Lewis base concentrations up to the optimal value of [Lewis base]/[BuLi], Rp increased much more than Ri, which resulted in a sharp increase of molecular weights. Beyond the optimal value of [Lewis base]/[BuLi] where all the positive counterions of the propagating ends were completely solvated, added Lewisbase might cause further dissociation of the associated [BuLi]n, leading to a larger increase of Ri as compared to Rp, and consequently to a decrease of DP.
    Additional Material: 3 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 28 (1990), S. 281-292 
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The γ-radiolysis behavior of poly(l-chloro-1-alkynes) \[ [\rlap{--} ({\rm CCI} = {\rm CR}\rlap{--} )_n ;{\rm R} = n - {\rm alkyl}] \] greatly changed with the length of alkyl group and with the presence or absence of oxygen. When γ-irradiated in air, poly(l-chloro-1-hexyne) (R = n-C4H9) decomposed to oligomers; its Gs value was as large as 5.4. When irradiated in vacuum, this polymer partly gelled. In contrast, poly(l-chloro-1-decyne) (R = n-C8H17) partly gelled even by irradiation in air. A high-dose irradiation of this polymer in vacuum resulted in the quantitative formation of a gel. The polymers irradiated in air contained carbonyl and hydroxyl groups, indicating the participation of oxidation reaction. Comparison with their thermolysis leads to a conclusion that these Cl-containing polyacetylenes are radiation-sensitive irrespective of their high thermal stability.
    Additional Material: 7 Ill.
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