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  • Articles  (12,278)
  • Springer  (10,662)
  • International Union of Crystallography  (1,277)
  • Oxford University Press  (339)
  • 1990-1994  (12,278)
  • 1990  (12,278)
  • Chemistry and Pharmacology  (12,278)
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  • Articles  (12,278)
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  • 1990-1994  (12,278)
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  • 1
    Electronic Resource
    Electronic Resource
    Polymerization of propylene by highly active catalysts synthesized with Mg(OEt)2/benzoyl chloride/TiCl4 (1990)
    Springer
    Polymer bulletin 23 (1990), S. 35-42 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Active centers have been studied in the polymerization of propylene using highly active Mg(OEt)2/Benzoyl chloride/TiCl4 catalysts activated with AlEt3. The method for the measurement of active centers is based on the inhibiting effect of CO on polymerization. The activity of the present catalysts, which is higher than that of TiCl3 or MgCl2-supported catalyst, is mainly due to the higher concentration of active centers by one order of magnitude. In order to investigate the stability of active centers during polymerization the number of active centers are compared at various polymerization times.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00983961
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  • 2
    Electronic Resource
    Electronic Resource
    The influence of total monomer concentration on the “reactivity” of ω-(p-vinylbenzyl ether) macromonomers of poly(2,6-dimethyl-1,4-phenylene oxide) determined from radiacal copolymerization experiments with butyl methacrylate (1990)
    Springer
    Polymer bulletin 23 (1990), S. 19-26 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The influence of the total monomer concentration on the radical reactivity ratio r1 of butyl methacrylate (BMA) (M1)-ω-(p-vinylbenzyl ether) macromonomer of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO-VBE) (M2) monomer pair was investigated. For two different molecular weights of the PPO-VBE macromonomer ( $$\bar M_n = 14,000$$ , $${{\bar M_w } \mathord{\left/ {\vphantom {{\bar M_w } {\bar M_n }}} \right. \kern-\nulldelimiterspace} {\bar M_n }} = 1.25$$ and $$\bar M_n = 5,300$$ $${{\bar M_w } \mathord{\left/ {\vphantom {{\bar M_w } {\bar M_n }}} \right. \kern-\nulldelimiterspace} {\bar M_n }} = 1.26$$ ), the determined reactivity ratio r1 decreases with the increase of the macromonomer concentration. Therefore, the reactivity of the macromonomer, 1/r1, follows the opposite trend. This dependence is due to micelles formation during copolymerization. This microsegregation process partitionates the comonomer concentrations between the bulk of solvent and around the growing chain and therefore, the experimental r1 is actually a product of the true reactivity ratio r1 0 and a partition coefficient k.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00983959
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  • 3
    Electronic Resource
    Electronic Resource
    2,2 bis (4-ethynylphenyl) hexafluoropropane (1990)
    Springer
    Polymer bulletin 23 (1990), S. 7-12 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The 2,2 bis(4-ethynylphenyl)hexafluoropropane is prepared via an original synthesis's process using a substitution of 2,2 bis(4-triflatephenyl) hexafluoropropane by trimethylsilyl acetylene. In this process ZnO is used to remove the triflate anion formed during the reaction. This diacetylenic compound melts at 37–38°C, exhibits an onset of polymerization at 120°C. After thermal treatment at 250°C, the obtained network shows a softening point at 300°C. This network remains stable in air up to 435°C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00983957
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  • 4
    Electronic Resource
    Electronic Resource
    Phase transition in swollen gels (1990)
    Springer
    Polymer bulletin 23 (1990), S. 89-94 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The DC conductivity of two networks — a poly(N,N-diethylacrylamide) network (N1) and a network prepared by the copolymerization of N,N-diethylacrylamide with 3 mol.% of sodium methacrylate (N2) — in deionized water in the temperature range 10–55°C was measured. While in the low-temperature range (expanded gel state) the volt-ampere (V-A) behaviour of both networks shows a semiconductive character (conductivity increases with increasing temperature), in the high-temperature range (collapsed gel state) the conductivity of the network N1 rapidly decreases with increasing temperature (metallic character). The presence of charges on the chain raises the conductivity and shifts the temperature of the change in conductivity to higher values. In the collapse region of the ionized network N2 anomalies were observed on the V-A characteristics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00983969
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  • 5
    Electronic Resource
    Electronic Resource
    Stereoregular oligomers of methyl methacrylate (1990)
    Springer
    Polymer bulletin 23 (1990), S. 157-162 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Packed column SFC has been found suitable for the rapid and detailed analysis of the isotactic and syndiotactic oligomers of MMA, when the temperature gradient technique was applied and the modifier was employed. Oligomer components from trimer to 20-mer separated completely. The heptamer fraction collected three times by SFC gave the 1H NMR spectrum of satisfactorily high S/N ratio; the spectrum agreed well with that of the standard sample. Separation by tacticity as well as by molecular weight was observed for the SFC of a mixture of the isotactic and syndiotactic oligomers. The isotactic oligomers had longer retention time than the syndiotactic oligomers of the corresponding degree of polymerization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00338495
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  • 6
    Electronic Resource
    Electronic Resource
    Phase transfer Pd(0) catalyzed polymerization reactions (1990)
    Springer
    Polymer bulletin 23 (1990), S. 177-184 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary 1,4-Bis[2-(4′,4″-diheptyloxyphenyl)ethynyl]benzene and 1,4-bis[2-(3′,3″-dimethyl-4′,4″-diheptyloxyphenyl)ethynyl]benzene were synthesized by a one pot phase transfer Pd(O)/Cu(I) catalyzed three step coupling of 1,4-diiodobenzene with 2-methyl-3-butyn-2-ol and the appropriate aryl halide. Both compounds display mesomorphic behavior similar to that of the analogous 1,2-(4,4′-dialkoxyaryl)acetylenes, except that the temperature window of each phase is stabilized, such that an enantiotropic mesophase is even observed in the derivative containing a methyl branch in the mesogen. Both compounds form mesomorphic EDA complexes with p-chloranil as electron acceptor, and display a depression of the nematic-isotropic transition temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00338498
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  • 7
    Electronic Resource
    Electronic Resource
    A new initiating system for the “living” polymerization of vinyl ethers leading to hydroxy-terminated polymers (1990)
    Springer
    Polymer bulletin 23 (1990), S. 185-190 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The reaction of trimethylsilyl iodide (TMSI) with 1,3-dioxolane (DXL) leads to the formation of 1-trimethylsiloxy-4-iodo-3-oxabutane. In combination with tetrabutyl ammonium triflate this compound can be used as an initiator for the polymerization of vinyl ethers. According to a living polymerization mechanism, the polymers are characterized by controlled molecular weights and narrow molecular weight distributions. The trimethylsiloxy head group originating from the initiation reaction is easily transformed into a primary hydroxyl function by hydrolysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00338499
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  • 8
    Electronic Resource
    Electronic Resource
    Retraction of the claim of ring expansion polymerization of isobutylene (1990)
    Springer
    Polymer bulletin 23 (1990), S. 525-527 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Some three years ago in a preliminary report from this laboratory we have proposed that the polymerization of isobutylene (IB) by the γ-tolyl-γ-valerolactone/BCl3 initiating system in CH3Cl or CH2Cl2 diluents at-30°C proceeds in a living manner by an unusual ring expansion mechanism and produces macrocyclic polyisobutylenes (PIBs) [1]. Extensive follow-up research confirmed the living nature of the polymerization, however, has failed to confirm the results of a key preliminary experiment upon which the proposition of macrocyclic polymer structure was based. Thus the results of a comparative hydrolysis/GPC experiment carried out with a relatively low molecular weight (Mn=5,400) PIB at -30°C under a blanket of N2 which gave a lower apparent molecular weight after hydrolysis than the original sample before hhydrolysis, could not be confirmed with higher molecular weight samples, i.e., with Mn=12,000, 17,000 and 30,000. As a consequence we wish to retract our earlier claim in regard to the synthesis of macrocyclic PIBs by certain lactone/BCl3 initiating systems but maintain that these polymerizations proceed in a living manner and yield asymmetric telechelic PIBs, e.g.,α-chloro-ε-carboxyl-PIBs [2].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00419972
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  • 9
    Electronic Resource
    Electronic Resource
    Characterization of surfaces of carbon fibres by scanning tunneling microscopy (1990)
    Springer
    Polymer bulletin 23 (1990), S. 555-562 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The experimental results obtained by scanning tunneling microscopy (STM) studies of different carbon fibres are presented and discussed. The comparative analysis of the STM images at scales from hundreds of nanometers down to atomic scale reveals the differences of surface features for carbon fibres processed from different precursors, polyacrylonitrile fibres and pitch. The high temperature treatment of carbon fibres — the so-called graphitization process — as used to improve the stress modulus induces drastically increased ordering phenomena at the atomic level. Structural information obtained by STM on the surface of the fibres as well as in their cross sectional areas is discussed in comparison with known results of diffraction studies. STM appears to be the new powerfull technique for the detailed structural studies of surfaces of carbon fibres. The perspectives of these studies are under discussion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01033098
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of the polymer structure and tacticity on the oxidizing ability of polyvinylpyridinium dichromate (1990)
    Springer
    Polymer bulletin 23 (1990), S. 295-298 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Poly (2-vinylpyridinium dichromate) oxidizes different alcohols to their corresponding carbonyl compounds more efficiently than poly (4-vinylpyridinium dichromate). Syndiotactic form of the 2-isomer is the most efficient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01032444
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  • 11
    Electronic Resource
    Electronic Resource
    Ionic conductivity and morphology of complexes formed by polyurethanes and lithium perchlorate (1990)
    Springer
    Polymer bulletin 23 (1990), S. 299-306 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Segmented polyether urethane (SEU) and urethaneurea (SEUU) were synthesized using ABA type triblock copolymer as a prepolymer, where A stands for poly(oxyethylene) and B stands for poly(oxytetramethylene). Lithium perchlorate was dissolved in SEU or SEUU to prepare LiC104 complexes (SEU/LiC104 and SEUU/LiC104) in film form. The highest conductivities observed here were 5.13x10-6 S cm-1 at 30°C and 3.34x10-5 S cm-1 at 50°C for LiC104/SEUU (oxyethylene-units content, 31 mol%). The ionic conductivity of these complexes was found to show the Arrhenius type temperature dependency. The effect of lithium perchlorate dissolution on the morphology of SEU and SEUU were also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01032445
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  • 12
    Electronic Resource
    Electronic Resource
    Further studies on the high-speed gel-spinning of ultra-high molecular weight polyethylene (1990)
    Springer
    Polymer bulletin 23 (1990), S. 353-359 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The high-speed spinning technique has been applied to very elastic solutions of ultra-high molecular weight polyethylene in paraffin oil in an attempt to produce a strong fiber in a one-step process. At a winding speed of 4000 m/min a fiber was produced with a tensile strength of 2.3 GPa, a Young's modulus of 46 GPa and a elongation at break of 6.5%. This fiber could not be hot drawn anymore. At a winding speed of only 1 m/min the same solution yielded after spinning and hot drawing a fiber with a tensile strength of 7.2 GPa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01032453
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  • 13
    Electronic Resource
    Electronic Resource
    Reaction of a diepoxide with a diisocyanate in bulk (1990)
    Springer
    Polymer bulletin 24 (1990), S. 31-38 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Reactions between a diepoxide and a diisocyanate can lead to copolymers having isocyanurate and oxazolidone rings in their chemical structure. Using Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR), we have studied the influence of catalysts such as an imidazole or a blocked isocyanate on the polymer formation. We have identified the nature of the exotherms observed in DSC experiments with the aid of FTIR spectroscopy and observed the influence of the molar ratio of the functional groups and the amount of catalyst. We have compared the influence of these catalysts with results obtained previously with a tertiary amine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00298318
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  • 14
    Electronic Resource
    Electronic Resource
    A radical-anion mechanism for the phase transfer catalyzed depolymerization of poly(2,6-dimethyl-1,4-phenylene oxide) (1990)
    Springer
    Polymer bulletin 24 (1990), S. 63-69 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary This paper describes a novel mechanism for the depolymerization of poly(2,6-dimethyl-1,4-phenylene oxide). This radical-anion mechanism is responsible for liquid (organic solvent)-liquid (aqueous inorganic base) phase transfer catalyzed depolymerization of poly(2,6-dimethyl-1,4-phenylene oxide). This depolymerization occurs through the addition of an aryloxy radical to the terminal phenolate anion of the polymer. The particular example discussed in this paper refers to the depolymerization of poly(2,6-dimethyl-1,4-phenylene oxide) in the presence of either 2,4,6-trimethylphenol or 4-tert-butyl-2,6-dimethylphenol. The similarities and differences between the phase transfer catalyzed polymerization of 4-bromo-2,6-dimethylphenol in the presence of 2,4,6-trimethylphenol and 4-tert-butyl-2,6-dimethylphenol and the phase transfer catalyzed depolymerization of poly(2,6-dimethyl-1,4-phenylene oxide) in the presence of the same two phenols are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00298323
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  • 15
    Electronic Resource
    Electronic Resource
    Dielectric measurements on liquid crystalline polymers derived from PETP (1990)
    Springer
    Polymer bulletin 24 (1990), S. 93-100 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Poly(ethylene terephthalate) PETP has been modified with a difunctional alcohol and acid in the molar relation 1:1. By dielectric relaxation measurements could be shown that the modification increases the segmental mobility (α-process). The local mobility (β-process) increases at smaller and decreases at higher concentrations of the modificators. A separation of the α-relaxation from the common relaxation process α+β could be observed with decreasing temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00298327
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  • 16
    Electronic Resource
    Electronic Resource
    Friction coefficient in gelatin and polyacrylamide gels (1990)
    Springer
    Polymer bulletin 24 (1990), S. 123-128 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The slow neutron transmission technique is used to measure the friction coefficient f of gel macromolecules moving against a solvent. It is shown that in the range of concentrations C=3–30%, f of gelatin gels is linearly dependent on C. The values of the monomer friction coefficient of gelatin and the friction coefficient at infinite dilution are determined. It is demonstrated that the friction coefficient of polyacrylamide gels varies as the viscosity of a solvent in a wide temperature range, however at temperatures below ∼25°C the deviation from proportionality is observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00298331
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  • 17
    Electronic Resource
    Electronic Resource
    Laser photocatalytic polymerization of phenylacetylene (1990)
    Springer
    Polymer bulletin 24 (1990), S. 135-141 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The polymerization of phenylacetylene induced by ultraviolet laser (266 and 355 nm) irradiation of W(CO)6 and W(CO)6-TiCl4 in CCl4 solvent was investigated. The weight-average molecular weights of the polymers reach 105. The infrared spectra indicate that the polymers have a trans-rich conjugated double bond structure. The influence of laser energy, laser wavelength and irradiation time on the polymerization was examined. Experimental data show that laser energy and wavelength are the most effective factors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00297309
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  • 18
    Electronic Resource
    Electronic Resource
    Interaction of α-TiCl3 with organoaluminium compounds and its correlation with propylene polymerization (1990)
    Springer
    Polymer bulletin 23 (1990), S. 513-518 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The characterization of polymer system by means of interaction reaction between the catalyst components of a Ziegler-Natta stereospecific system formed by TiCl3 and AlEt3 in heptane was carried out. The experimental results show that the formation and decay of the active centers are interdependent. The interaction of the catalyst components, which causes a destruction of the solid phase, influences the rate of polymerization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00419970
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  • 19
    Electronic Resource
    Electronic Resource
    Physical ageing in glassy liquid crystalline poly(p-hydroxy-benzoic acid-co-ethylene terephtalate) (1990)
    Springer
    Polymer bulletin 23 (1990), S. 83-88 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Glassy liquid crystalline poly(p-hydroxy-benzoic acid-co-ethylene terephthalate) is after rapid cooling from temperatures above Tg in a non-equilibrium state and exhibits physical ageing. It is shown that enthalpy and volume decrease with increasing annealing time. At the same undercooling, with respect to middle temperature of the major glass transition (Tgl), the rate of the equilibration process is significantly slower in the studied polymer than in an ordinary glassy amorphous polymer. The presence of a constraining ETP-rich phase exhibiting a 25 K higher glass temperature than Tgl may be the cause for this retarded enthalpy relaxation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00983968
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  • 20
    Electronic Resource
    Electronic Resource
    Maximum crystal growth rate and its corresponding state (1990)
    Springer
    Polymer bulletin 23 (1990), S. 111-118 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary For the temperature dependence of linear crystal growth rate, the activation energy for the molecular transport could be expressed in terms of the equation of either WLF or Arrhenius. On the basis of the Arrhenius expression, the corresponding state of the crystal growth rate was formulated theoretically as $${{\ln ({G \mathord{\left/ {\vphantom {G {G_{max} }}} \right. \kern-\nulldelimiterspace} {G_{max} }})} \mathord{\left/ {\vphantom {{\ln ({G \mathord{\left/ {\vphantom {G {G_{max} }}} \right. \kern-\nulldelimiterspace} {G_{max} }})} {\ln ({{G_{max} } \mathord{\left/ {\vphantom {{G_{max} } {G_o }}} \right. \kern-\nulldelimiterspace} {G_o }})}}} \right. \kern-\nulldelimiterspace} {\ln ({{G_{max} } \mathord{\left/ {\vphantom {{G_{max} } {G_o }}} \right. \kern-\nulldelimiterspace} {G_o }})}} = {{(T_{cmax} - T)^2 } \mathord{\left/ {\vphantom {{(T_{cmax} - T)^2 } {T(T_m - T)}}} \right. \kern-\nulldelimiterspace} {T(T_m - T)}}.$$
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00983972
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  • 21
    Electronic Resource
    Electronic Resource
    Polyurethane-polystyrene interpenetrating polymer networks synthesized in the presence of a common solvent (1990)
    Springer
    Polymer bulletin 23 (1990), S. 141-148 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Interpenetrating polymer networks (IPN's) of polyurethane and polystyrene were synthesized by simultaneous polymerization. The effect of compositional variation and the presence of a common solvent in the reaction medium on the rate of polymerization, the onset of phase separation, and the morphology of product were investigated. 1,4-Dioxane was selected as a common solvent by the swelling experiment. The rate of network formation in the early stage of polymerization process increased with increasing the polyurethane composition. When 1,4-dioxane was present in the reaction medium, the extent of reaction of both components at the onset of phase separation was higher than that of IPN's by bulk preparation. The morphology of final product was influenced by the extent of reaction at the onset of phase separation. The density, glass transition behavior, and thermal stability were also studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00338493
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  • 22
    Electronic Resource
    Electronic Resource
    Copolymerization via zwitterion (1990)
    Springer
    Polymer bulletin 23 (1990), S. 171-175 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Copolymers of N-phenylmaleimide and ethyleneimine were synthesized in acetonitrile in the absence of initiator. The copolymers are insoluble in solvents such as DMF, CHCl3, DMSO, CH3OH, H2O. The copolymer composition as determined by elemental analyses depends on the initial monomer ratio. The thermal stability of copolymers was studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00338497
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  • 23
    Electronic Resource
    Electronic Resource
    Synthesis and characterization of high molecular weight poly(tert.butyl acrylate) (1990)
    Springer
    Polymer bulletin 24 (1990), S. 39-43 
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    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract High molecular weight poly(tert. butyl acrylate) s have been synthesized anionically using a technique derived from that of Teyssié et al. It was established that under proper conditions the sites remained living, allowing proper control of the molecular weight and yielding samples with narrow molecular weight distributions.
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    Synthesis and characterization of poly (N-butyl-3,6-carbazolediyl) (1990)
    Springer
    Polymer bulletin 24 (1990), S. 17-22 
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    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Poly (N-butyl-3,6-carbazolediyl) was synthesized by electrochemcial reduction of the NiBr2, 2,2′bipyridine/3,6 dibromo N-butylcarbazole system in N,N dimethylacetamide. The favorable interactions between solvent and butyl groups lead to the solubilization of the electroactive polymer in organic medium and allowed the determination of macromolecular and structural features by means of classical methods. From 13C NMR investigations it was concluded to a Π conjugation centered on the nitrogen atom of the carbazolic structure.
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    URL: http://dx.doi.org/10.1007/BF00298316
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    Initiation of cationic polymerization by tetramethylene zwitterions from tetracyanocyclobutanes (1990)
    Springer
    Polymer bulletin 24 (1990), S. 45-52 
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The initiating ability of tetramethylene zwitterions formed from cyclobutane adducts of donor olefins with TCNE was investigated. Polar solvents increased the ability of vinyl ether-TCNE cyclobutane adducts to initiate the cationic polymerization of N-vinylcarbazole. The concept of charge separation in the tetramethylene zwitterions was also investigated.
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    URL: http://dx.doi.org/10.1007/BF00298320
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    Phase transfer catalyzed depolymerization of poly(2,6-dimethyl-1,4-phenylene oxide) in the presence of either 2,4,6-trimethylphenol or 4-tert-butyl-2,6-dimethylphenol (1990)
    Springer
    Polymer bulletin 24 (1990), S. 71-78 
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    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary This paper describes the phase transfer catalyzed depolymerization of poly(2,6-dimethyl-1,4-phenylene (xide) performed in the presence of either 2,4,6-trimethylphenol or 4-tert-butyl-2,6-dimethylphenol. The structure of the resulting polymers is compared to that of the corresponding polymers obtained by the phase transfer catalyzed polymerization of 4-bromo-2,6-dimethylphenol in the presence of either 2,4,6-trimethylphenol or 4-tert-butyl-2,6-dimethylphenol. Polymers obtained by depolymerization display a bimodal molecular weight distribution while those obtained by polymerization a monomodal molecular weight distribution. The polymers obtained by direct polymerization present structural units derived from some side reactions. These side reactions do not occur during the depolymerization process.
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    URL: http://dx.doi.org/10.1007/BF00298324
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    Study of the stoichiometric polyelectrolyte complex between chitosan and carboxymethyl cellulose (1990)
    Springer
    Polymer bulletin 23 (1990), S. 307-313 
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The polyelectrolyte complex (PEC) between chitosan and carboxymethyl cellulose was studied. Turbidimetric measurements revealed that the amount of stoichiometric PEC increased gradually as the solution of one polyelectrolyte was added to the other; the turbidity of the solution reached a maximum for the stoichiometric ratio of the reacting polyelectrolytes in the mixture. At pH 4,0 the composition of the complex is very near to equimolarity. IR spectra and thermal analysis of the PEC exhibited significant differences from those of the 1:1 mixture of the starting polyelectrolytes.
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    Novel copolymerizations of methyl vinylidene cyanide with electron-rich vinyl monomers (1990)
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    Polymer bulletin 24 (1990), S. 151-156 
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract At 28° the spontaneous reactions of methylvinylidene cyanide (MVCN) with p-methoxystyrene, p-trimethylsiloxystyrene, styrene, isobutyl vinyl ether, ethyl vinyl ether and trimethylsilyl vinyl ether yielded alternating copolymers of potential interest as new piezoelectric materials. MVCN copolymerized with vinyl acetate in low yield using radical initiator and ZnCl2. Attempted homopolymerizations of MVCN with various initiators gave only low molecular weight oligomers, particularly trimers.
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    URL: http://dx.doi.org/10.1007/BF00297311
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    Sulfonation of chlorine-containing polymers: Sulfonation of various model tert-alkyl chlorides (1990)
    Springer
    Polymer bulletin 24 (1990), S. 165-172 
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    Notes: Summary tert-Alkyl chlorides of the structure R-C(CH3)2Cl, where R-methyl, ethyl, tert-butyl, and neo-pentyl, were reacted with a stoichiometric quantity of acetyl sulfate at room temperature in methylene chloride diluent. Reaction conversion was monitored as a function of time using 1H NMR; structure of the sulfonated products was characterized using 1H and 13C NMR. Reactivity toward sulfonation increased with increasing size of the R group. In all cases the structure of the products was the same as would be expected from sulfonation of the olefin which results from dehydrochlorination of the tert-chloride. The observed behavior was consistent with a mechanism involving dehydrochlorination followed by addition of SO3 to yield a zwitterionic intermediate. Depending upon structure, the zwitterion may either eliminate a proton to form one or more isomeric β,γ-unsaturated sulfonic acids, or it may rearrange to form a five-membered γ-sultone. This chemistry, which is particularly useful in the synthesis of ionomers, represents a direct route to alkyl sulfonic acids when the alkyl halide is the natural starting point in the synthesis.
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    Preparation of a water soluble polyester surfactant and its use in the emulsion polymerization of styrene (1990)
    Springer
    Polymer bulletin 23 (1990), S. 367-371 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The synthesis procedure of Chen and Liu (1) was used to prepare a polyester surfactant from dimethyl 5-sulfoisophthalate, sodium salt, polyoxyethylene (MW 200) and phthalic anhydride by a two step esterification process. The surfactant has the unique structural features of multiple ionic groups and polyoxyethylene chains for hydrophilicity and aromatic ester linkages for hydrophobicity. The polyester surfactant exhibited a CMC of 0.25% (w/v) and a surface tension lowering of 23 dynes/cm. The use of the surfactant as stabilizer for the emulsion polymerization of styrene produced some unusual results. While the rate of polymerization was independent of surfactant concentration, the number of particles increased as N ∝ [S]0.91. The molecular weight of polystyrene produced was low and found not to be a function of surfactant concentration. The structural features of the surfactant suggest that a depletion stabilization mechanism might be operative in this system.
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    Characterization of block copolymers by size exclusion chromatography (1990)
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    Polymer bulletin 23 (1990), S. 389-395 
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Poly(ethyl methacrylate-b-deuterated methyl methacrylate), poly(styrene-b-methyl methacrylate), and poly(styrene-b-dimethylsiloxane)diblock copolymers have been characterized by means of size exclusion chromatography (GPC) apparatus fitted with four detectors in series, viz continuous viscometer, UV spectrophotometer, low angle light scattering photometer, and differential refractometer. The continuous measurements of the scattered light intensity, the limiting viscosity number, the concentration, and the chemical composition permits complete determination of the molecular characteristics of block copolymers.
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    Electron spin resonance measurement of nitroxy probes mobility, attached to a polymer through a spacer arm (1990)
    Springer
    Polymer bulletin 23 (1990), S. 419-423 
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    Notes: Summary Stable nitroxide radical probes are attached to styrene-divinylbenzene gel type resins through spacer arms, the length of which being 1 to 7 methylene groups. Results of electron spin resonance analysis which allows to estimate the local viscosity are discussed. Mobility of the nitroxide probes generally increases with the number of CH2 groups, the effect being compared to a decrease of cross-linking density.
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    Infrared linear dichroism spectroscopy by a double modulation technique (1990)
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    Polymer bulletin 23 (1990), S. 447-454 
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary A linear IR dichroism experiment has been devised using a FTIR instrument in combination with a photoelastic modulator. Based on the Mueller-Stokes calculus, a method to directly obtain the absorbance spectra Av parallel and Av perpendicular from the modulated interferogram is developped, which allows the sensitive evaluation of the dichroic ratio. The photoelastic modulator, in combination with a FTIR instrument, offers high sensitivity, high speed, excellent signal to noise ratio and a broad spectral range from 3300 to 850 cm-1. First experimental results obstained from SBS block copolymer are reported.
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    Preparation of alkyl acrylate-acrylic acid copolymers by simultaneous hydrolysis and polymerization (1990)
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    Polymer bulletin 23 (1990), S. 497-504 
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The ability of concentrated nitric acid (65% HNO3) to initiate reactions of polymerization when in contact with acrylic and methacrylic acids and esters at room temperature in the absence of other reagents has been studied in this laboratory. In a previous paper, we presented the results when the reaction was applied to methacrylic monomers. This work reports data obtained with methyl and ethyl acrylates; high molecular weight ester-acid copolymers were produced. The nature of the products and the course of the reaction are discussed.
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    The localisation model of rubber elasticity. II (1990)
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    Polymer bulletin 23 (1990), S. 529-533 
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The effect of the spatial localization of a network chain by surrounding chains is incorporated into the chain probability distribution function and the network free energy is then calculated using the statistical mechanical formalism for constrained systems. In addition to a term having the classical ‘Gaussian’ form, the resulting expression contains another term which depends on both the cross-link density of the network and the plateau modulus of the uncross-linked melt.
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    Studies on the molecular weight dependence of tacticity of anionically prepared PMMAs by on-line GPC/NMR (1990)
    Springer
    Polymer bulletin 23 (1990), S. 549-554 
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Several PMMA samples prepared in toluene with anionic initiators such as t-C4H9MgBr, n-C4H9MgCl, 1,1-diphenylhexyllithium, t-C4H9Li and t-C4H9Li(n−C4H9)3Al complex were analyzed by the on-line GPC/NMR method using a 500 MHz 1H NMR spectrometer as a real-time detector of GPC. The molecular method for a short time (≤60 min per sample) with a small amount of the sample (≈1 mg). The plots of intensities of the α-methyl proton resonances due to mm- and rr-triads against elution time showed the variation of tacticity with molecular weight of the PMMA. On the basis of the results, the natures of active species in the polymerizations were discussed.
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    Unsaturated polyesters (1990)
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    Polymer bulletin 23 (1990), S. 577-581 
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The polymerization of maleic anhydride and 1,3-propylene glycol was carried out using p-toluenesulphonic acid as catalyst. The resulting material has been characterized by ir and H1nmr spectroscopy, end group analysis and gel permeation chromatography. The percentage isomerization of maleate to fumarate has been correlated with the extension of polycondensation and the steric hindrance between the condensed functional groups.
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    129Xe NMR as a probe of the effect of crosslinking on the amorphous phase structure of solid polymers (1990)
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    Polymer bulletin 23 (1990), S. 605-608 
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    Notes: Summary 129Xe NMR of xenon adsorbed in a solid EPDM rubber shows the presence of at least four distinct regions in the amorphous phase of this polymer. Changes in the relative amounts of these environments are observed upon crosslinking indicating that changes in the amorphous phase structure of the polymer have occurred.129Xe NMR provides a direct probe of the formation of a more condensed amorphous phase of the polymer matrix due to the crosslinking reaction.
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    Electrical conductive and magnetic properties of conjugated tetrathiolate nickel polymers (1990)
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    Polymer bulletin 23 (1990), S. 631-636 
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Three tetrathiolate (tetrathiafulvalenetetrathiolate, ethylenetetrathiolate, and butadienetetrathiolate) nickel polymers are prepared. The polymers contain mixed valence Ni ions and are ESR active based on low-spin d8 Ni (III) species. Magnetic susceptibility measurement in the range of 30–60 K suggests and antiferromagnetic interaction between the Ni ions in the polymers. Below 30K a weak ferromagnetic interaction is observed. Chemically oxidized polymers are ESR inactive, while electrical conductivity is greatly enhanced.
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    Copolymerization of tetrahydrofuran and propylene oxide (1990)
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    Polymer bulletin 24 (1990), S. 507-512 
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Copolymerization of tetrahydrofuran and propylene oxide catalyzed by modified H2SO4.SO3 system has been studied. Sodium perchloride was used to replace perchloric acid as co-catalyst. The copolymerization rate was obviously accelerated when using the new H2SO4.SO3−NAClO4 catalyst system. The reaction became less sensitive to the moisture.
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    A metal sorbent with an unbound complexing agent: polyethylenimine-bead cellulose (1990)
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    Polymer bulletin 24 (1990), S. 533-538 
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    Notes: Summary A sorbent was prepared with branched polyethylenimine fixed on bead cellulose without chemical reaction. The “jack-in-the-box” effect was used by means of which a part of the originally adsorbed PEI remains, after treatment with strong acid, almost irreversibly fixed to cellulose. The sorbent contains 1.4–3.0 mmol N/g of dry matter and is able to bind some double-charged cations from acid solutions, both from buffered media (pH 2–4) and from hydrochloric acid (1–4 M).
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    Structure characterization of alginate and conformational behaviors of various alkali-metal alginates in solution (1990)
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    Polymer bulletin 24 (1990), S. 551-557 
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    Notes: Summary The M/G ratio, i. e., number-ratio of D-mannuronate (M) to L-gluronate (G), and diad (MM, GG, MG, etc.) and triad (MMM, MMG, MGM, etc.) frequencies were determined with 100 MHz 13C-NMR spectra for two alginate samples, M-rich and G-rich samples. The M/G ratios obtained were in accord with those determined from chemical analysis on hydrolyzed products fairly well. Molecular chain dimensions in solution were investigated by viscosity method for five alkali-metal alginates carrying Li, Na, K, Rb and Cs, and the results were discussed based on ion radius and electronegativity of alkali-metals. Finally, ion-exchange characteristics of these alginates by Ca++ ion were interpreted with M/G ratio and electronegativity.
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    Synthesis and thermodynamics properties of poly(ethylene oxide) prepared in diphenylzinc-water (1990)
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    Polymer bulletin 24 (1990), S. 589-596 
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    Notes: Abstract Poly (ethylene oxide) (PEO) samples, obtained using diphenylzinc-water as initiator, have been used to determine some characteristics of this polymer. The unperturbed dimensions of PEO have been obtained by the application of various theoretical treatments to viscometry measurements carried out in a good solvent. The following relationship between intrinsic viscosity and weight average molecular weight has been obtained [ŋ]/dL.g•1 = 3.99x10•4M0.69 W.
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    Nitroso labeling in electron-irradiated LDPE (1990)
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    Polymer bulletin 24 (1990), S. 607-612 
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    Notes: Summary The nitroso labeling method (1) has been used to demonstrate its possibilities for the characterization of irradiated polyethylene (LDPE) with respect to its crosslinkings and oxygen functionalities. ESR spectra of nitroso labeled LDPE consist of the superposition of the signals resulting from three different radicals. It has been shown that a relative estimation of the ketone content is possible in irradiated LDPE samples even at low concentrations thus giving a sensitive method for this functional group in polyethylene.
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    Phase diagram of borate-PVA system: Sol-gel transition and demixtion (1990)
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    Polymer bulletin 24 (1990), S. 633-640 
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    Notes: Summary We study the formation of reversible gels induced by addition of borax in aqueous poly(vinylalcohol). Under suitable conditions, sol, gel or demixed phase is observed. We present a qualitative interpretation of the the number of inter-polymer complexes which is governed by the complexation equilibrium.
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    Polyelectrolytes and ionomers (1990)
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    Polymer bulletin 24 (1990), S. 671-671 
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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    An absolute measure for stereoblock and heterotactic polymers (1990)
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    Polymer bulletin 24 (1990), S. 305-308 
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    Notes: Summary A criterion (°) for testing stereoblock and heterotactic polymers is developed. The criterion takes values between 1 and-1, a value of 1 is indicative of a pure stereoblock polymer and a value of-1 indicates a pure heterotactic polymer. The criterion (°) is compared with persistence ratio (ρ) and average stereochemical sequence length. The importance of δ as an aid in the synthesis of stereoblock polymers is discussed.
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    Effect of end group of side chains on surface properties of diblock copolymers (1990)
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    Polymer bulletin 24 (1990), S. 333-340 
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The A-B diblock copolymers with comb shape structure were prepared from styrene (St) and either methacrylate of poly(ethyleneglycol) monomethyl ether (MPEGM) or methacrylate of poly(ethyleneglycol) (HPEGM). The surface chemical analysis of the polymer at air-solid interface by means of X-ray photoelectron spectroscopy (XPS) revealed the enrichment of MPEGM for MPEGM/St and St for HPEGM/St diblock copolymers, which indicated that the end group of the side chain determined surface composition. Dynamic contact angle measurements revealed that the migration of hydrophilic poly(ethyleneglycol) at solid-water interface occurred upon immersing the film specimen in water.
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    Structure analysis of conductive polymer systems: Poly-4-vinylpyridine and poly(butadiene-b-4-vinylpyridine) with 7,7′,8,8′-tetracyanoquinodimethane (1990)
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    Polymer bulletin 24 (1990), S. 325-332 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The structure analysis of two conductive polymer systems-poly-4-vinylpyridine and poly(butadiene-b-4-vinylpyridine) with 7,7′,8,8′-tetracyanoquinodimethane (TCNQ)-was done by X-ray diffraction, scanning tunneling microscopy (STM) and FTIR. The charge transfer complex formed between the pyridine group and the known electron acceptor, TCNQ, is supposed to be the conductive element in these systems. In order to understand the structure of this complex, a model compound, the complex of 4-ethylpyridine (4EP) with TCNQ, 4EP/TCNQ2, was studied by the mentioned methods. It appears that there are two crystalline modifications of the model compound with different type of stacks of the TCNQ molecules. In polymer systems only one type of the complex is dominant as revealed by joint analysis of X-ray diffraction diagrams, STM and FTIR data. In the STM image of the polymer surface one can distinguish that molecular stacks with periodicities of 4.1 Å in a row are separated (12.5Å) from each other. Such organization is similiar to the one observed in conductive charge transfer complexes such as tetrathiofulvalene (TTF) with TCNQ. The ordered molecular domains are scattered on the polymer surface and take part in the formation of the conductive network.
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    URL: http://dx.doi.org/10.1007/BF00306583
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    Copolymerization of 5-vinyl-1,3-benzodioxole with n-butyl acrylate and methyl methacrylate (1990)
    Springer
    Polymer bulletin 24 (1990), S. 385-389 
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    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Copolymers of 5-vinyl-1, 3-benzodioxole (VBD) with n-butyl acrylate and methyl methacrylate were synthesized. The copolymers were synthesized according to a designed experiment methodology and reactivity ratios were estimated using a nonlinear least squares error-in-variables procedure. The values of r1 and r2 obtained show that VBD is slightly less reactive than styrene in similar copolymerization reactions.
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    URL: http://dx.doi.org/10.1007/BF00294091
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    4,4′-diisocyanatoazobenzene a mesogen for liquid crystalline polyurethanes? (1990)
    Springer
    Polymer bulletin 24 (1990), S. 413-419 
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    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The mesomorphic properties of 4,4′-diisocyanatoazobenzene were investigated by polarizing microscopy and DSC. It shows a nematic phase when thoroughly purified by distillation. The nematic range, however, is smaller than that of other liquid crystalline diisocyanates like 4,4′diisocyanatophenyl benzoate. A number of binary hard segment type polyurethanes was made with several diols as chain extenders and in addition ternary copolyruethanes containing two different mesogenic diisocyanates. They are crystalline materials with poor solubility. The melt temperatures of these polyurethanes are higher than those of the corresponding polymers with 4,4′-diisocyanatophenyl benzoate. Liquid crystalline behaviour could not be observed in any of the polymers probably because of the high melting transitions and relatively lower izotropization temperatures which result from the higher rigidity and symmetry of the azobenzene structure.
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    URL: http://dx.doi.org/10.1007/BF00294095
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    Influence of the melt temperature on the thermoplastics crystallization process (1990)
    Springer
    Polymer bulletin 24 (1990), S. 445-450 
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    ISSN: 1436-2449
    Keywords: Poly(oxymethylene) ; Poly(ether-ether-ketone) ; DSC ; Kinetics ; Melt temperature ; Crystallization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The influence of the melt temperature (T1) on the crystallization kinetics and the morphology of two semicrystalline polymers: poly(oxymethylene): T m 0 =198° C and poly(ether-ether-ketone) T m 0 =380° C) was investigated using thermal analysis and optical microscopy. For different melt temperatures (T1), isothermal and nonisothermal crystallizations were analysed using the AVRAMI and OZAWA models. Using different analyses, for both polymers we observed a spherulitic growth with the following influence of the melt temperature on the number of spherulites: -T1〈T m 0 produces many small spherulites -T1〉T m 0 gives rise to few large spherulites
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    Synthesis and characterization of poly(N-tert-alkylmaleimide)s (1990)
    Springer
    Polymer bulletin 24 (1990), S. 459-466 
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    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract N-tert-Butylmaleimide (tBMI) polymerized readily in the presence of a radical initiator in spite of its bulky N-substituent to give a high molecular weight and less-flexible poly(substituted methylene). From kinetic investigation for the polymerization of tBMI with 2,2′-azobisisobutyronitrile (AIBN) in benzene, it was revealed that the rate of polymerization (R p) was expressed as R p=k [AIBN]0.51[tBMI]1.4, and the overall activation energy was 99.6 kJ/mol. The high polymerization of tBMI was assumed to result from the decrease in the rate of bimolecular termination between rigid polymer radicals bearing a bulky substituent. The flexibility of the polymer chain was examined by the viscometric and light scattering methods, and the effect on the polymerization reactivity was discussed.
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    URL: http://dx.doi.org/10.1007/BF00395565
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    Living cationic polymerization of isobutyl vinyl ether, 2 (1990)
    Springer
    Polymer bulletin 24 (1990), S. 513-519 
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    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Living cationic polymerization of isobutul vinyl ether (IBVE), initiated by1-iodo-1-(2-methyl propyloxy)-ethane (1) and tetraalkylammonium perchlorate yields polymers of well defined molar masses and end groups. The controlled introduction of end groups was confirmed by a model reaction and was then applied to introduce and azo initiator function. The resulting polymeric initiator was used for the synthesis of a blockcopolymer.
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    Percolation analysis on free radical linear polymerization with instantaneous initiation (1990)
    Springer
    Polymer bulletin 24 (1990), S. 539-543 
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    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Free radical linear polymerization with instantaneous initiation was simulated on the simple cubic lattice. The monomer conversion, polydispersity index and average degree of polymerization were predicted by using the percolation model which was based on computer-simulated self-avoiding walks on the lattice. The adjusting parameters such as reactivity, termination modes, coordination number of given lattice were introduced.
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    Ethynyl terminated ethers. Synthesis and thermal characterization of 2,2 bis (ethynyl-4-phenylcarbonyl-4-phenoxy-4-phenyl) propane and 2,2 bis (ethynyl-4-phenylsulfonyl-4-phenoxy-4-phenyl) propane (1990)
    Springer
    Polymer bulletin 24 (1990), S. 577-582 
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    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Two ethynyl end-capped ethers 2,2 Bis [ethynyl-4-phenylsulfonyl-4-phenoxy-4-phenyl] propane and 2,2 Bis [ethynyl-4-phenylcarbonyl-4-phenoxy-4-phenyl] propane have been prepared by a three steps synthesis each. They exhibit melting point followed by the thermal polymerisation of the ethynyl groups in the 200–250°C range. Curing lead to thermoset materials where Tg are respectively of 240°C and not detectable.
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    Linear viscoelastic behavior of narrow molecular weight distribution 1,4 polybutadiene: Comparison with Doi-Edwards theory of reptation (1990)
    Springer
    Rheologica acta 29 (1990), S. 88-97 
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    ISSN: 1435-1528
    Keywords: Doi-Edwards theory ; reptation ; viscoelastic behavior ; polybutadiene ; molecular weight distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Linear viscoelastic behavior of narrow molecular weight distribution 1,4 polybutadiene samples $$(\bar M_w /\bar M_n \sim 1.2)$$ with molecular weights between 42500 and 779000 has been correlated with molecular structure using a simple modification of the Doi-Edwards theory of reptation. The entire GPC curve is required for the calculations of viscoelastic behavior. The plateau modulus obtained from the experimental data is comparable to literature values, while the equilibrium compliance (which is indicative of polydispersity) is greater than values reported in the literature for nearly monodisperse polybutadienes. Reasonable agreement between theory and experiment is obtained over the entire molecular weight range. The agreement between theory and experiment using the GPC curve is better than that obtained by assuming the polymer to be monodisperse or by using the Doi fluctuation model. The model appears to break down for a more polydisperse sample $$(\bar M_w /\bar M_n = 1.7)$$ . This study indicates that it may be possible to use the Doi-Edwards theory to explain the viscoelastic behavior of narrow MWD polybutadienes without introducing any new concepts into the theory (fluctuations, constraints release, etc.).
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    Announcement (1990)
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    Rheologica acta 29 (1990), S. 174-174 
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    ISSN: 1435-1528
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
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    URL: http://dx.doi.org/10.1007/BF01332386
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    Experimentelle Bestimmung Binghamscher Stoffparameter (1990)
    Springer
    Rheologica acta 29 (1990), S. 163-169 
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    ISSN: 1435-1528
    Keywords: Bingham ; yieldstress ; differentialviscosity ; falling-ball experiments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Abstract An experiment is described to determine the two Bingham material constants (yield stressτ f and differential viscosity $$\hat \eta $$ ) of viscoplastic fluids. The principle of the experiment is based on the falling-ball technique, where the stationary velocities of balls with different diameters and densities are measured. The required theory to calculate the Bingham material constants is illustrated. Experimental results of aqueous Carbopol 941-solutions are reported. These are listed in dependence of concentration in tables and diagrams.
    Notes: Zusammenfassung Es wird ein Versuchsaufbau beschrieben, der es ermöglicht, die beiden Binghamschen Stoffparameter (Fließspannungτ f und differentielle Viskosität $$\hat \eta $$ ) einer viskoplastischen Flüssigkeit zu bestimmen. Der Versuch basiert auf dem Kugelfallprinzip, bei dem in einem Zylinder die stationäre Sinkgeschwindigkeit von Kugeln im Schwerefeld gemessen werden. Neben der Geschwindigkeit gehen das spezifische Gewicht der Flüssigkeit sowie die Geometrie und das spezifische Gewicht verschieden großer Kugeln in die Berechnung der Stoffparameter ein. Die zugehörige Theorie wird kurz erläutert. Im experimentellen Teil werden wäßrige Carbopol 941-Lösungen untersucht. Die Ergebnisse sind in Abhängigkeit der Konzentration tabellarisch angegeben und graphisch dargestellt.
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    Orientation-dependent rotational diffusion coefficient of rod-like macromolecules in semi-dilute solution (1990)
    Springer
    Rheologica acta 29 (1990), S. 172-173 
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    ISSN: 1435-1528
    Keywords: Rod-likemolecules ; Doi-Edwards theory ; rotationaldiffusion ; topologicalinteraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The integral describing the topological interaction of rod-like macromolecules in the Doi-Edwards theory has been computed for the orientational distribution functionΨ expressed in spherical harmonics. It is shown that the orientation-dependent rotational diffusion coefficientD r may easily be calculated.
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    URL: http://dx.doi.org/10.1007/BF01332385
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    Anisotropic conduction of heat caused by molecular orientation in a flowing polymeric liquid (1990)
    Springer
    Rheologica acta 29 (1990), S. 175-181 
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    ISSN: 1435-1528
    Keywords: Anisotropy ; thermalconductivity ; orientation ; Graetz-Nusselt problem ; polymer processing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract To demonstrate the influence of molecular orientation on the heat conduction in a flowing polymeric liquid, we consider a variant of the Graetz-Nusselt problem. A polymeric liquid is flowing between two flat, parallel plates with a sudden change in the wall temperature. The temperature distribution in the entrance region is calculated numerically taking viscous dissipation into account. It is assumed that the material properties are independent of the temperature. It is shown that the change in the temperature distribution in the fluid caused by molecular orientation is large enough to affect polymer processing significantly.
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    URL: http://dx.doi.org/10.1007/BF01331353
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    On the role of stress-induced migration on time-dependent terminal velocities of falling spheres (1990)
    Springer
    Rheologica acta 29 (1990), S. 182-191 
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    ISSN: 1435-1528
    Keywords: Fallingspheres ; viscoelasticfluids ; stress-inducedmigration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract There is experimental evidence to suggest that even under steady-state conditions the velocity of solid spheres or bubbles moving through viscoelastic fluids can become time dependent. One of the possible explanations offered for interpreting this phenomenon has been the generation of a polymer depleted layer in the line of passage of the particles, which disappears due to the counterbalancing effect of molecular diffusion in the long range. We have done some careful experiments and measured these concentrations to show that no such depletion layers are formed. Alternative explanations of the phenomenon have been examined and the importance of the possible effects of microstructures generated through temporary associations has been emphasised.
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    The motion of rodlike particles in the pressure-driven flow between two flat plates (1990)
    Springer
    Rheologica acta 29 (1990), S. 192-203 
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    ISSN: 1435-1528
    Keywords: Rodlikeparticle ; shearflow ; Newtonianfluid ; non-Newtonianfluid ; wall effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The motion of freely suspended rodlike particles has been observed in the pressure-driven flow between the two flat plates of a Hele Shaw flow cell at low Reynolds numbers. Data are reported for rodlike particles with aspect ratios of 12.0 suspended in a Newtonian fluid for gap thickness to particle length ratios of 3, 6, and 20; and for rodlike particles with aspect ratios between 5 and 8 in a non-Newtonian fluid (79.25 wt.% water, 20.2 wt.% glycerine, and 0.55 wt.% polyacrylamide). For the Newtonian fluid, the time-dependent orientation of the particles near and far from walls was shown to be in quantitative agreement with Jeffery's theory for ellipsoids suspended in a simple shear flow if an effective aspect ratio is calculated from the experimental period of rotation. Particles aligned with the flow direction and less than a particle half-length from a wall interacted irreversibly with the wall. For the non-Newtonian fluid, the timedependent orientation far from a wall was shown to be in qualitative agreement with Leal's theory for a second-order fluid; however, particles that were aligned with the flow direction and were near walls did not rotate.
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    Experimental investigations of the stability limit of the helical flow of pseudoplastic liquids (1990)
    Springer
    Rheologica acta 29 (1990), S. 453-461 
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    ISSN: 1435-1528
    Keywords: Flowstability ; helicalflow ; vortices ; pseudoplasticliquid ; Couetteflow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The stability of the laminar helical flow of pseudoplastic liquids has been investigated with an indirect method consisting in the measurement of the rate of mass transfer at the surface of the inner rotating cylinder. The experiments have been carried out for different values of the geometric parameterη = R 1/R 2 (the radius ratio) in the range of small values of the Reynolds number,Re 〈 200. Water solutions of CMC and MC have been used as pseudoplastic liquids obeying the power law model. The results have been correlated with the Taylor and Reynolds numbers defined with the aid of the mean viscosity value. The stability limit of the Couette flow is described by a functional dependence of the modified critical Taylor number (including geometric factor) on the flow indexn. This dependence, general for pseudoplastic liquids obeying the power law model, is close to the previous theoretical predictions and displays destabilizing influence of pseudoplasticity on the rotational motion. Beyond the initial range of the Reynolds numbers values (Re〉20), the stability of the helical flow is not affected considerably by the pseudoplastic properties of liquids. In the range of the monotonic stabilization of the helical flow the stability limit is described by a general dependence of the modified Taylor number on the Reynolds number. The dependence is general for pseudoplastic as well as Newtonian liquids.
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    Linear and branched poly(butyleneisophthalate): Activation energy for melt flow (1990)
    Springer
    Rheologica acta 29 (1990), S. 469-474 
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    ISSN: 1435-1528
    Keywords: Poly(butyleneisophthalate) ; shearviscosity ; temperatureshift factor ; flowactivation energy ; branchedpolyester
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Several poly(butyleneisophthalate)s of different molecular weight, both linear and randomly branched, were synthetized by bulk polymerization and studied in the molten state with a capillary rheometer in the temperature range 190–220°C. The viscosity shift factors showed to be well correlated to temperature by an Arrhenius-type equation. The melt-flow activation energy at constant shear stressE τ was found to be 15±1 kcal/mol for both linear and branched samples, whereas for polydisperse poly(butyleneterephthalate) and poly(ethyleneterephthalate) it was found previously that random long-chain branching substantially increases the activation energy. An analysis of our results and of those available in the literature shows that the influence of branches on the temperature coefficient of viscosity of polymers is still a subject open to discussion.
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    A note on similarity-type flows of elastico-viscous fluids (1990)
    Springer
    Rheologica acta 29 (1990), S. 485-488 
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    ISSN: 1435-1528
    Keywords: Similarity-type flows ; suction ; elastic fluids ; flow reversal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract A study is undertaken to ascertain non-Newtonian effects in steady flows of elastic fluids due to an infinite rotating disk when there is suction across its surface. The fluids considered are of a class for which the similarity-type solution of von Kármán is an exact solution. It is shown that the presence of elasticity (of the type considered) does not result in flow reversal, the disk acting as a centrifugal fan as in Newtonian flow.
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    Methode zum Messen des Langzeitverhaltens von Thermoplasten (1990)
    Springer
    Rheologica acta 29 (1990), S. 252-258 
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    ISSN: 1435-1528
    Keywords: Filledthermoplastics ; opticalstrain measurement ; long-termbehavior ; biaxialloading ; nonlinearviscoelasticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Abstract A new optical device for strain measurement in long-term tension and torsion tests is presented. The new system has been compared with others and the results of the experiments with glass bead and short, glas-fiber-filled Polyamid 6 show that it works well. With a dead-weight loading machine used it is possible to perform combined tension/torsion creep experiments or simple tension and simple torsion tests. The materials under consideration here exhibit nonlinear behavior in tension as well as in torsion tests. Under combined loading, which is tensile stress with a superimposed torsional stress, or vice versa, the amounts of the strains compared with those of the one-dimensional stress state are increasing. The fillers produce different reinforcement effects. The bead-filled system is stiffer when subjected to a torsional load, which may be explained by different load carrying mechanism in tension and torsion. The glass-fiber-filled system is stiffer in axis direction, because the fibers are aligned to a considerable extent by the flow of the melt during molding.
    Notes: Zusammenfassung Es wird eine neue berührungslose optische Dehnungsmeßeinrichtung für biaxiale Langzeit-Zug- bzw. Torsionsversuche vorgestellt. Die Ergebnisse der Versuche an kugel- und kurzglasfasergefülltem Polyamid 6 (PA 6) zeigen, daß dieses System genügend genau arbeitet. Das untersuchte Material weist sowohl im Zugversuch als auch im Torsionsversuch nichtlineares Verhalten auf. Bei überlagerten Zug/Torsions-Belastungen verschieben sich die Dehnungen, verglichen mit denen bei gleicher einaxialer Last zu höheren Werten. Durch die Füllstoffzugabe ergeben sich unterschiedliche Verstärkungseffekte. Die faserverstärkten Proben sind erwartungsgemäß eher in Richtung der Rohrachse verstärkt, während das kugelgefüllte System eine höhere Verstärkungswirkung bei Torsionsbelastung erkennen läßt.
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    Rheology of an LDPE melt in reversing multi-step shear and elongational flows (1990)
    Springer
    Rheologica acta 29 (1990), S. 281-297 
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    ISSN: 1435-1528
    Keywords: Separability ; irreversibility ; KBKZ model ; reversing step strains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The hypotheses of separability and irreversibility, which have greatly improved the accuracy of constitutive models of the KBKZ type are tested in reversing step shear and elongational deformations. A reversing double-step deformation is a severe test for constitutive models and a new rheometer has been developed to perform this type of deformation, both in shear and elongation, in a single machine. Test results of a commercial low-density polyethylene melt are reported here with model predictions. In particular, the performance of the KBKZ-type integral model and a differential analogue is considered. Wagner's idea of irreversibility and the KBKZ-equivalent ideas of Larson are tested with these data. While these versions show a moderate agreement with experiment, the irreversible integral model gives an accurate fit and emerges clearly as the best description of polymer melts in these flows.
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    On the relaxation of shear and normal stresses of viscoelastic fluids following constant shear rate experiments (1990)
    Springer
    Rheologica acta 29 (1990), S. 261-280 
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    ISSN: 1435-1528
    Keywords: Relaxation ; first normalstress difference ; Gaussianerror function ; stress test ; cone and platerheometer ; mirror relation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract By means of a cone and plate rheometer the relaxation of the shear stress and the first normal stress difference in polymer liquids upon cessation of a constant shear rate were examined. The experiments were conducted mostly in a high shear rate region of relevance for the processing of these materials. The relaxation behavior at these shear rates can only be measured accurately under extremely precise specifications of the rheometer. To determine under which conditions the integral normal thrust is a convenient measure for the relaxing local first normal stress difference the radial distribution of the pressure in the shear gap was measured. The shape of relaxation of both the shear stress and the first normal stress difference could be closely approximated for the entire measured shear rate and time range by a two parameter statistical function. In the range of measured shear rates, one of the parameters, the standard deviationS, is equal for the shear and the normal stress, and is independent of the shear rate within the limit of experimental error. The second parameter, the mean relaxation timet′ 50,τ of the shear stress andt′ 50,σ of the first normal stress difference, can be calculated approximately from the viscosity function and only a single relaxation experiment.
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    Consistency tests for start-up and cessation deformations of viscoelastic fluids (1990)
    Springer
    Rheologica acta 29 (1990), S. 298-309 
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    ISSN: 1435-1528
    Keywords: K-BKZ model ; straincoupling ; start-upexperiments ; cessationexperiments ; consistency relations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The time-dependent shear stress and first normal stress difference were measured for a polystyrene solution for start-up and cessation-flow experiments over a relatively wide range of shear rate. Consistency tests for the K-BKZ model were applied to the data, and it was concluded that the K-BKZ equation generally does not satisfactorily describe the start-up and cessation data. Modified consistency tests were developed using a strain-coupling constitutive equation, and the evidence suggests that most of the differences between the predictions of the K-BKZ theory and experiment can be explained by including a strain-coupling effect in the rheological constitutive equation.
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    Cancellation of errors in the Higashitani-Pritchard treatment of hole pressures generated by viscoelastic liquids in creeping flow past a transverse slot (1990)
    Springer
    Rheologica acta 29 (1990), S. 310-322 
    Details
    ISSN: 1435-1528
    Keywords: Hole pressure ; error cancellation ; non-Newtonian fluid, HPBL equations ; modified hole pressure relation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Analytical studies of the hole pressure for non-Newtonian creeping flow past a transverse slot are pursued with particular interest in the formulation of Higashitani and Pritchard (HP). To correct the flaws in the treatment of HP's original work, a modified hole-pressure relation (MHPR) is employed. Some important mathematical properties of the MHPR are presented. By studying the MHPR in streamline coordinate formulation, we find a fortuitouserror cancellation phenomenon in the derivation of the HP formula: namely, the error caused by one key flaw is fortuitously cancelled out by the error introduced through another key flaw. For second-order fluids and Tanner's “viscometric model” (under certain assumptions) the cancellation of errors is proved to be exact. It is this cancellation of errors that provides a theoretical explanation for the paradox between an apparently flawed derivation and the fortunate success of the HP prediction.
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    URL: http://dx.doi.org/10.1007/BF01339886
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    A novel geometry for rheological characterization of viscoelastic materials (1990)
    Springer
    Rheologica acta 29 (1990), S. 323-331 
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    ISSN: 1435-1528
    Keywords: Rheometry ; variablerange ; pseudosphere geometry ; viscoelasticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract A novel geometry for generating a viscometric flow presents advantages of both cone and plate and parallel plate geometries, regarding uniform shear field and adjustable range of measurement. Kinematics and dynamics of the generated flow have been described mathematically utilizing an orthogonal curvilinear coordinate system based on the shapes of the shearing surfaces which are similar to the surface that generates the flow. Simple equations that allow the calculation of quantities of experimental interest in the rheological characterization of liquid materials, namely, shear rate, shear stress and two normal stress differences, have also been derived. The geometry, called pseudosphere, was tested with two types of fluids (Newtonian and pseudoplastic). Results show that the geometry can be used with low viscosity liquids (Newtonian liquids) by only adjusting the gapH. The behavior of pseudoplastic fluids for both low and moderately high viscosity could also be studied with this geometry. Very reproducible results were obtained when compared with those obtained with cone and plate geometry. Regions of lower shear rate could be studied using only the pseudosphere geometry.
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    URL: http://dx.doi.org/10.1007/BF01339887
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    A numerical comparison of two decoupled methods for the simulation of viscoelastic fluid flows (1990)
    Springer
    Rheologica acta 29 (1990), S. 342-351 
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    ISSN: 1435-1528
    Keywords: Oldroyd-B fluids ; die flows ; stick-slip problem ; finite element method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Two decoupled methods for the finite element solution of the planar stick-slip transition problem with Oldroyd-B fluids, namely the method of characteristics and the Lesaint-Raviart technique, are presented and compared. These procedures are used for the local treatment of the stress transport equation imbedded in the constitutive law and allow the approximation of stresses with discontinuous shape functions. Computations are carried out up to a Deborah number of 4 and the methods are shown to yield fairly similar results.
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    Etude du régime de mise en mouvement dans un viscosimètre de Couette à cylindres coaxiaux (1990)
    Springer
    Rheologica acta 29 (1990), S. 332-341 
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    ISSN: 1435-1528
    Keywords: Couette viscometer ; start-up motion ; imposed-speed ; inertia ; Maxwellfluid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Résumé L'utilisation du viscosimètre de Couette à cylindres coaxiaux pour l'évaluation des propriétés rhéologiques et l'établissement de la loi d'écoulement des fluides nécessite généralement la connaissance du taux des cisaillement en chaque point de l'entrefer et à tout instant. Cette quantité en général inconnue peut être approchée par des expressions mathématiques satisfaisantes pour l'écoulement à couple appliqué mais d'autant plus grossières qu'on s'éloigne du régime stationnaire pour l'écoulement à vitesse imposée. La plupart des approximations généralement utilisées sont obtenues sous l'hypothèse d'un fluide dont n'influence pas l'écoulement et pour un entrefer petit. Notre travail étudie la limite de validité de certaines approximations du taux de cisaillement pour l'écoulement transitoire à vitesse imposée. Dans le contexte de la mise an évidence des propriétés viscoélastiques de certains fluides nous avons choisi d'étudier l'écoulement de montée en vitesse plus utilisé que l'écoulement de relaxation sur l'exemple d'un fluide de type Maxwell. Nous montrons que le domaine de validité de ces approximations dépend, de la viscosité et la densité du fluide, de l'entrefer du dispositif et d'un temps caractéristique représentant la durée de la sollicitation imposée au fluide. L'influence de ces différents paramètres s'exprime par l'intermédiaire d'un nombre adimensionnel (Re) ayant la forme d'un nombre de Reynolds.
    Notes: Abstract The use of the Couette viscometer with coaxial cylinders for the evaluation of rheological properties and the establishment of behaviour laws of fluids, generally requires the knowledge of the shear rate at each instant and at any point in the gap. This quantity, which is generally unknown, can be approximated by simple mathematical expressions which are satisfactory for the applied torque flow but become less accurate as one moves away from the stationary state for the imposed speed flow. Most of the commonly used approximations are obtained under the assumption that the inertia of the fluid does not affect the flow and that the gap is small. In this work, we study the limit of the validity of certain approximations for the shear rate in an imposed speed transient flow on the example of a fluid of the Maxwell type. It is shown that the range of validity of these approximations depends on the viscosity and the density of the fluid, on the gap of the viscometer, and finally on a characteristic time representing the period under which an external perturbation is imposed to the fluid. The influence of these different parameters is expressed through a dimensionless number (Re) having the form of a Reynolds number.
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    The relaxation of polymers with linear flexible chains of uniform length (1990)
    Springer
    Rheologica acta 29 (1990), S. 400-408 
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    ISSN: 1435-1528
    Keywords: Relaxation spectrum ; monodisperse polymers ; scaling ; glass transition ; plateau modulus ; recoverable compliance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The analysis of dynamic mechanical data indicates that linear flexible polymer chains of uniform length follow a scaling relation during their relaxation, having a linear viscoelastic relaxation spectrum of the formH(λ) = n 1 G N 0 × (λ/λ max) n1 forλ≤λ max. Data are well represented with a scaling exponent of about 0.22 for polystyrene and 0.42 for polybutadiene. The plateau modulusG N 0 is a material-specific constant and the longest relaxation time depends on the molecular weight in the expected way. At high frequencies, the scaling behavior is masked by the transition to the glassy response. Surprisingly, this transition seems to follow a Chambon-Winter spectrumH(λ) = Cλ−n2, which was previously adopted for describing other liquid/solid transitions. The analysis shows that the Rouse spectrum is most suitable for low molecular-weight polymersM ≈ M c , and that the de Gennes-Doi-Edwards spectrum clearly predicts terminal relaxation, but deviates from the observed behavior in the plateau region.
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    Finite shear strain behavior of a crosslinking polydimethylsiloxane near its gel point (1990)
    Springer
    Rheologica acta 29 (1990), S. 423-432 
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    ISSN: 1435-1528
    Keywords: Gelpoint ; gelequation ; polydimethylsiloxane ; shear modification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract A power law distribution of relaxation times, large normal stress differences, and physical rupture of molecular network strands dominate the shear behavior of polymers at the gel point (critical gels). This is shown in a series of well-defined experiments with increasing magnitude of shear on a model-network polymer system consisting of a linear, telechelic, vinyl-terminated poly-dimethylsiloxane (PDMS) and a four-functional siloxane crosslinker. Stable samples were prepared by stopping the crosslinking reaction at different extents of reaction in the vicinity of the gel point (GP). The Gel Equation has been shown to be valid up to strains of about 2 when using a finite strain tensor. Larger strains have been found to disrupt the network structure of the crosslinking polymer, and introduce a mechanical delay to the gel point. A sample that was crosslinked beyond the gel point (p〉p c ) can be reduced from the solid state to a critical gel, or even to a viscoelastic liquid, depending on the magnitude of shear strain. As a consequence, the relaxation exponent of a critical gel created under the influence of shear is less than that of a quiescently crosslinked critical gel.
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    The squeezing flow of a model suspension fluid (1990)
    Springer
    Rheologica acta 29 (1990), S. 433-441 
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    ISSN: 1435-1528
    Keywords: Squeezingflows ; fibre suspensions ; boundary element method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The paper is concerned with the squeezing flow of a model suspension fluid. The numerical solution obtained by a time-dependent Boundary Element Method is compared to an asymptotic solution at large radius. It is found that the kinematics are Newtonian in character, and the fibres quickly align themselves radially. Consequently, the squeezing force is only weakly dependent on the initial orientations of the fibres and the device can be used for measuring the effective viscosity of the suspension. The effective viscosity found from the squeezing flow agrees surprisingly well with experimental data and numerical data derived from the falling sphere geometry at low volume fractions (Φ 〈 0.1).
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    Flow behaviour of molten 2,4,6-trinitrotoluene (TNT) between concentric cylinders (1990)
    Springer
    Rheologica acta 29 (1990), S. 462-468 
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    ISSN: 1435-1528
    Keywords: Flow curve ; coaxial cylinderviscometer ; trinitrotoluene melt ; turbulence ; viscosity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The flow behaviour of pure and commercial molten TNT when subjected to very high rates of shear in a rotational viscometer over the temperature range 82.0 to 95.4°C is presented. All data obtained suggest that the behaviour of molten TNT is Newtonian, contrary to the conclusions of some published work, and the temperature dependence of the viscosity of pure TNT is adequately described by an Arrhenius-type relationship of the formη = A e B/T whereA = 0.000 541,B = 3 570 andT is the Kelvin temperature. A similar relationship is obtained for commercial TNT. Under some instrumental conditions discontinuities are seen in the shear stress—shear rate flow curves. An analysis of these discontinuities shows them to be caused by the transition from laminar to turbulent flow. Possible implications for processibility and initiation of explosives are discussed.
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    The stability of the helical flow of pseudoplastic liquids in a narrow annular gap with a rotating inner cylinder (1990)
    Springer
    Rheologica acta 29 (1990), S. 442-452 
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    ISSN: 1435-1528
    Keywords: Flowstability ; helical flow ; vortices ; power-lawviscosity ; Couette flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The stability of a laminar helical flow of pseudoplastic liquids in an annular gap with a rotating inner cylinder is investigated theoretically. The analysis is carried out under the assumption of a torroidal form of the secondary flow (torroidal Taylor vortices) for the narrow gap geometry. The power law model has been applied to describe the pseudoplasticity of liquids. The problem of the stability has been formulated with the aid of the method of small disturbances, and solved using the Galerkin method. In order to describe the stability limit the Reynolds and Taylor numbers defined with the aid of the mean viscosity value have been introduced. It has been found that pseudoplasticity has a considerably destabilizing influence on the Couette motion as well as on the helical flow in the initial range of the Reynolds number values (Re〈30). A decrease of the flow index value,n, is accompanied by a decrease of the critical value of the Taylor number. This destabilizing effect of pseudoplasticity vanishes in the range of the larger values of the Reynolds number. In the rangeRe〉30, the stability limit of the flow of pseudoplastic liquids can be described by a general dependence of the critical valueTa c onRe, which is consistent with results obtained for the case of Newtonian fluids.
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    Announcements (1990)
    Springer
    Rheologica acta 29 (1990), S. 489-489 
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    ISSN: 1435-1528
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
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    URL: http://dx.doi.org/10.1007/BF01376802
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    On the spring-dashpot representation of linear viscoelastic behaviour (1990)
    Springer
    Rheologica acta 29 (1990), S. 482-484 
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    ISSN: 1435-1528
    Keywords: Linear visco-elasticity ; spring-dashpot models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Consideration is given to a simple four constant description of linear viscoelastic behaviour. It is shown that the equivalent mechanical models can be physically unrealistic, with negative moduli. Furthermore, such models satisfy the requirements of i) a positive, monotonic decreasing relaxation function, and ii) positive dissipation. By implication, it is concluded that the spring-dashpot description of linear viscoelasticity is not completely general.
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    A model of zinc-nickel alloy electrodeposition in an industrial-scale cell (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 1-10 
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    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper analyses continuous alloy plating of steel strip with the use of a rate model that accounts for migration and homogeneous equilibria in the mass-transport boundary layer adjacent to the cathode. The model predicts the effect of bath composition, temperature, electrolyte velocity, and current density on the alloy composition and current density distribution within the cell. The effect of a slight taper of the interelectrode gap was also considered. The results were used to evaluate which of several currently used electrogalvanizing cells are most likely to succeed in producing coats of uniform zinc-nickel alloy composition. It is demonstrated that mass-transfer of the zinc is a critical factor under typical industrial conditions and that electrolyte injection counter to the strip movement is important for application of an electrodeposit uniform in composition.
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    The effect of nickel on the mechanism of the initial stages of zinc electrowinning from sulphate electrolytes. Part II. Investigations on aluminium cathodes alloyed with iron impurities (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 17-22 
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    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The effect of the alloying element Fe on the electrochemical behaviour of Al cathodes during the initial stages of zinc electrowinning was studied, using scanning electron microscopy, cyclic voltammetry, atomic absorption and X-ray microprobe analysis techniques. It is shown that underpotentially deposited zinc submonolayer inhibits the discharge of hydrogen ions onto Fe aggregates — alloying element.
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    An ac impedance study of the fractal geometry of silver films electrodeposited within a polymer matrix (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 23-25 
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    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Silver films (∼10−6m) have been electrodeposited within a polymer matrix (∼10−5 m) of polyvinylidene fluoride trifluoroethylene copolymer 60-40 cast on the surface of a stainless steel electrode. It is shown that the fractal geometry of the polymer-metal interface, which is not open to direct observation, can be characterized by means of ac impedance measurements made on the electrode in acetonitrile solution.
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    Mechanism of enhancement of the corrosion of steel by alternating currents and electrocatalytic properties of cycled steel surfaces (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 26-31 
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    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The effect of potential cycling on the growth of oxide layers on steel is analysed. It is shown that the redox reactions in the oxide layers formed are diffusion controlled and it is proposed that the transport of OH− is the limiting step of growth. The relationship of these results to ac corrosion is discussed and it is shown that alternating currents flowing through structures can accelerate the corrosion rate if the potential excursion encompasses the reduction of an ‘inner’ oxide layer, not only by the growth of hydrated oxide layers, but also by the observed enhancement of the electrocatalytic properties towards oxygen reduction of the oxide layers formed on cycling.
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    Transition metal-based hydrogen electrodes in alkaline solution — electrocatalysis on nickel based binary alloy coatings (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 32-38 
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    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Nickel-molybdenum, nickel-zinc, nickel-cobalt, nickel-tungsten, nickel-iron and nickel chromium binary alloy codeposits, obtained through electrodeposition methods on mild steel strips, have been characterized with the objective of qualitatively comparing and assessing their electrocatalytic activities as hydrogen electrodes in alkaline solution. It has been concluded that their electrocatalytic effects for the hydrogen evolution reaction rank in the following order: Ni-Mo 〉 Ni-Zn (after leaching Zn in KOH) 〉 Ni-Co 〉 Ni-W 〉 Ni-Fe 〉 Ni-Cr 〉 Ni plated steel. Further investigations on the alloy electrocatalysts have revealed that the cathodic overpotential contribution to the electrolysis voltage can be brought down by 0.3 V when compared with conventional cathodes. The best and most stable hydrogen evolving cathode, based on nickel-molybdenum alloy, exhibited an overpotential of about 0.18 V for over 1500 h of continuous electrolysis in 6m KOH at 300 mA cm−2 and 353 K. The salient features of the coatings, such as physical characteristics, chemical composition, crystal structure of the alloy phases and the varying effects of the catalytic activation method were analysed with a view to correlating the micro-structural characteristics of the coatings with the hydrogen adsorption process. The stability under open-circuit conditions, the tolerance to electrochemical corrosion and the long term stability of nickel-molybdenum alloy cathodes were very encouraging. An attempt to identify the pathway for the hydrogen evolution reaction on these alloy coatings was made, in view of the very low apparent activation energy values obtained experimentally.
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    Nucleation and growth of anodic films on stainless steel alloys. II. Kinetics of repassivation of freshly generated metal surfaces (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 45-53 
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    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The kinetics of anodic film growth on six types of freshly generated stainless steel surfaces have been investigated electrochemically as a function of electrode potential and electrolyte composition. Repassivation of a scratch scar showed that initial growth of a passive film is controlled by ion migration in a high electric field obeying an inverse logarithmic rate law at passive potentials. The rate of growth was dependent on the electrode potential and the chloride ion concentration in the electrolyte. Three kinetically distinct regions were observed and are discussed in terms of film growth, film dissolution and pitting.
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    The effect of nickel on the mechanism of the initial stages of zinc electrowinning from sulphate electrolytes. Part I. Investigations on a spectrally pure aluminium cathode (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 11-16 
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    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The effect of nickel ions on the mechanism of the initial stages of zinc electrowinning was studied using scanning electron microscopy (SEM) and cyclic voltammetry. It is shown that nickel ions are deposited simultaneously onto the zinc crystals which are being formed and onto the still exposed aluminium cathode. As a result of the catalytic activation of the hydrogen ion discharge during the initial stages of the process, conditions are created for the formation of hydrogen bubbles on the uncovered aluminium cathode.
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    Mediated electrosynthesis with cerium (IV) in methanesulphonic acid (1990)
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    Journal of applied electrochemistry 20 (1990), S. 209-215 
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    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Methanesulphonic acid has been found to solubilize the Ce(III)/Ce(IV) couple. This makes cerium mediated electrosynthesis practical for commercial production of several carbonyl compounds. Results are presented for the electrochemical generation of Ce(IV) in methanesulphonic acid and for naphthalene oxidation to 1,4-naphthoquinone using Ce(IV).
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    Overall mass transfer in swirling decaying flow in annular electrochemical cells (1990)
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    Journal of applied electrochemistry 20 (1990), S. 216-222 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Mass transfer coefficients between an electrolyte solution and the inner cylinder of an annulus were determined experimentally, using the electrochemical technique, for both laminar and turbulent swirling flows of a liquid induced by means of a tangential inlet in the annular gap. The average mass transfer coefficients were determined as a function of the axial distance from the entrance, for various diameters of the inlet duct and thicknesses of the annular space, for a Reynolds number range of 100 to 5900. Enhancement of mass transfer up to 400% was achieved in comparison to that obtained in fully developed axial flow. Correlations of the experimental data, taking into account the geometrical and hydrodynamic parameters influencing the overall mass transfer, are presented.
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    Nucleation and growth of anodic films on stainless steel alloys I. Influence of minor alloying elements and applied potential on passive film growth (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 223-230 
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    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The influence of minor alloying elements (Mo, V, W) when added to a Fe18Cr alloy on the ability of a passive film to nucleate and grow on a freshly generated metal surface, and on the subsequent stability of the film was investigated as a function of electrolyte composition and applied potential using a scratch chronoamperometric technique. Mo and V decreased the rate of active dissolution prior to passivation, allowing the onset of passivation to occur more rapidly, and also improved the stability of the passive film, especially to attack by Cl− in acidic (H2SO4, HClO4) solutions. W additions had a detrimental effect on the repassivation behaviour of Fe18Cr. Repassivation of the scratch scars was evaluated, from the current transients, in terms of the number of layers of surface film formed.
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    The effect of pulsed reverse current on the polarization behaviour of acid copper plating solutions containing organic additives (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 196-208 
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    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The polarization behaviour of acid copper solutions containing polyethers, sulphopropyl sulphides and chloride ions was studied using both direct and pulsed reverse current. The effect of these additives on the rest potentials of copper foils immersed in the electrolyte was also studied. Polyethers were found to have an inhibiting effect on the deposition of copper whereas the sulphopropyl sulphides produced a stimulating (i.e. depolarizing) effect. Chloride ion concentration was found to have an influence on the adsorption characteristics of the polyether. The use of pulsed reverse current in solutions containing both polyether and sulphopropyl sulphide was found to inhibit the adsorption/diffusion of the sulphopropyl sulphide at the cathode surface. Thus at higher current densities, above 2 A dm−2, the inihibiting effect of the polyether produced a shift in the cathodic polarization potential to more negative values as compared with an equivalent current density using direct current. At lower current densities, below 2 A dm−2, the depolarization effect of the sulphopropyl sulphide was still effective. This effect of pulsed current on additive containing solutions can improve dramatically the metal distribution in low current density areas on plated items. This was illustrated by plating Hull cell panels using both pulsed and direct current.
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    Morphological changes in the electrodes of phosphoric acid fuel cells operating under open circuit voltage conditions (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 235-239 
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    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper reports the experimental evidence for morphological changes that occur at the electrodes of phosphoric acid fuel cells (PAFC) under very severe (OCV) conditions. In addition, the dissolution of Pt-supported crystallites in H3PO4 is demonstrated by Transmission Electron Microscopy (TEM) confirming previous results already reported in the literature. Finally, the experimental data are discussed on the basis of an analysis of the reaction rates and models for the corrosion mechanism is postulated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01033600
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  • 94
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    Exclusion of CO and CO2 from ammonia synthesis gas by an electrocatalytic process (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 240-244 
    Details
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A new exclusion process for CO and CO2 from ammonia synthesis gas has been proposed: this takes place at room temperature and atmospheric pressure. The process is based on the electrochemical reduction of CO and CO2 to methanol proceeding at a mediated electrode via homogeneous catalysis. The maximum percentages of CO and CO2 excluded from the initial gas were about 1.5 and 4.1%, respectively, with a mediated electrode of 82.8 cm2 area in a reaction time of 5 h. The amount of excluded CO and CO2 was equivalent to the sum of moles of methanol formed and gases dissolved into the solution alone. The electroreduction of CO and CO2 was more efficient at three-phase (electrode/solution/gas) and at two-phase (electrode/solution) interfaces, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01033601
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  • 95
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    Voltammetric behaviour of platinum in aqueous solutions containing sodium hypophosphite (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 245-251 
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    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The anodic and cathodic behaviour of polycrystalline Pt in sodium hypophosphite solutions has been investigated by cyclic voltammetry. In acid solutions the voltammograms show that, owing to the presence of the reducing agent, electrooxidation of species related to H3PO3 occurs in the potential range 0.6 to 1.4 V with respect to NHE. In alkaline solutins the presence of NaH2PO2 partially inhibits the HER and displaces the formation of the oxygen monolayer on platinum to higher potentials. The voltammetric peaks are attributed to the electrooxidation of the products resulting from the chemical decomposition of NaH2PO2 in contact with the Pt surface.
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    URL: http://dx.doi.org/10.1007/BF01033602
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  • 96
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    Phosphate-bonded composite electrodes for hydrogen evolution (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 252-259 
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    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A new process of cementing metallic powders to produce high surface area cathodes for alkaline water electrolysis is described. The binding compound is a tridimensional polymer of aluminium phosphate (AlPO4). Phosphate-bonded composite electrodes give a low-polarization performance for hydrogen evolution in 1m KOH aqueous solution in the case of 95 wt% Pt and 98 wt% Ni. When electrode materials are prepared with nickel powder, the electrocatalytic activity for the hydrogen evolution reaction, the chemical stability and the electrical conductivity depend on the Ni content and morphology of the electrode. The best performance and chemical stability with Ni as the starting material are obtained for spiky filamentary particles produced by the decomposition of nickel carbonyl.
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    URL: http://dx.doi.org/10.1007/BF01033603
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  • 97
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    Investigation of O2 reduction in alkaline media on macrocyclic chelates impregnated on different supports: influence of the heat treatment on stability and activity (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 260-268 
    Details
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Several macrocyclic chelates impregnated on different carbon supports were investigated using a three-phase electrode. Pyrolysed CoTMPP on treated Vulcan yields comparable results to dispersed Pt. XPS investigations reveal, for the most stable compounds, either a special bond with carbon (CoTMPP) or in some cases nitride formation (MoNPc). With the most active compounds, the MeN4 unit is preserved after heat treatment. The affinity of carbon or nitrogen with the metal compared to the O2 affinity is essential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01033604
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  • 98
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    Electrogenerative oxidation of model alcohols at packed bed anodes (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 269-280 
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    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The electrogenerative oxidation of dissolved ethanol and 2-propanol in aqueous 1 to 3 M sulphuric acid electrolyte was investigated at several types of packed bed anodes in ion exchange membrane separated cells. The operation of these electrogenerative cells which incorporated a platinum-catalysed commercial oxygen gas-diffusion-type cathode is described. It appears that for dissolved normal primary alcohols composite Teflon-platinum fuel-cell-type electrodes favour aldehyde formation while ‘platinum on graphite’ electrodes favour carboxylic acid formation. Oxidation of dissolved 2-propanol could be controlled to give acetone exclusively.
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    URL: http://dx.doi.org/10.1007/BF01033605
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  • 99
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    In situ activation of nickel cathodes by sodium molybdate during alkaline water electrolysis at constant current (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 281-288 
    Details
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The nickel cathode undergoes significant deactivation at 100 mA cm−2 in 30 wt% KOH at 70°C containing KOH metallic impurities. The time dependence of the potential reveals two distinct regions: the first due to hydrogen absorption, while the Tafel parameters, charge transfer resistance and double-layer capacitance remain fairly constant; the second due to the electrodeposition of metallic impurities as manifested by SEM pictures, EDX analysis and cyclic voltammograms. The resulting deactivation is due mainly to the increase in the Tafel slope, although the electrode impedance reveals a significant increase in electrode roughness. The hydrogen discharge at 100 mA cm−2 in 30 wt% KOH containing 4mm sodium molybdate largely attenuates the deactivation process owing to hydrogen absorption and the deposition of impurities. Thein situ activation is ascribed to the formation of a spongy molybdenum-base deposit on the nickel cathode during the first day of water electrolysis.
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    URL: http://dx.doi.org/10.1007/BF01033606
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  • 100
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    Effect of hydrogen on discharge behaviour of the nickel oxide electrode (1990)
    Springer
    Journal of applied electrochemistry 20 (1990), S. 377-380 
    Details
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The effect of hydrogen on the discharge behaviour of the nickel oxide electrode has been investigated in 30% KOH solution at 25°C. Open-circuit potentials of the nickel oxide electrodes, previously fully charged, decrease more rapidly in a hydrogen atmosphere than in an argon environment. Voltammograms of the nickel oxide electrode show that the amount of cathodic charge decreases considerably when the nickel oxide electrode is exposed to hydrogen rather than to argon. These results, along with X-ray diffraction data, indicate that hydrogen can increase the self-discharge rate of the nickel oxide electrode as a result of reduction of β-NiOOH to β-Ni(OH)2 and the simultaneous oxidation of hydrogen. In addition, hydrogen can produce changes in the nickel oxide electrode during charge that persist to modify discharge behaviour and open-circuit potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01076044
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