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  • Polymer and Materials Science  (18)
  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 47 (1996), S. 340-343 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Silver cluster formation in bulk block copolymer films (static-cast) and in thin films (microtomed or spin-coated) was investigated by transmission electron microscopy. In all cases, the silver clusters were formed predominantly within the original silver-containing microdomains. A greater degree of control of cluster formation and a narrower cluster size distribution were achieved in the thin films of block copolymers. The interfaces between domains of the heterogeneous copolymers and the free interfaces of the thin film specimens all played an important role in nucleation and growth of clusters.
    Additional Material: 7 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 45 (1994), S. 301-307 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A new “Durham” polyacetylene precursor monomer (substituted tricyclo[4.2.2.02,5]deca-3,7,9-triene) was synthesized, and improved synthetic pathways to two existing precursor monomers were developed. Polymers of these three precursor monomers, as well as a bis-trifluoro substituted precursor monomer, were synthesized using ring opening metathesis polymerization (ROMP) with a tungsten alkylidine initiator. The kinetics of conversion (precursor polymer to polyacetylene) were studied for each of the four precursor polymers using differential scanning calorimetry (DSC). Percent age conversion vs. time data were fit to the Avrami expression often used to describe the kinetics of bulk of crystallization of polymers. The parameter K of the Avrami expression was assumed to depend on temperature according to an Arrhenius expression. In this way, an equation with three constants was obtained that completely describes the kinetics of conversion of a particular polyacetylene precursor polymer. Values for the constants depended on the type of substituent on the precursor polymer. Because the kinetics are well described by the Avrami expression, it is proposed that “nucleation” and “propagation” processes are involved in the conversion of the precursor polymers to polyacetylene.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Three triblock copolymers of nylon-6 (Ny6) and aromatic poly(sulfone ether) (PSuE) were investigated relative to their morphology and their thermal properties. Generally, the nylon blocks of the three Ny6-PSuE-Ny6 samples were very short (between 5 and 16 monomer units). Heterogeneous, microphase-separated morphologies could be observed for all samples, independent of the processing conditions, i.e., solvent casting or melt cooling. However, the process conditions were highly influential on the formation of the supramolecular structures (i.e., spherulites), especially when the crystallizable block was short.
    Additional Material: 6 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 45 (1992), S. 1223-1227 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Over the temperature range of 20 to 90°C, the equilibrium solubility of methane or argon in a star-branched polystyrene-polybutadiene (SB) block copolymer can be reliably estimated from a volume-fraction-weighted average of the homopolymer solubilities; the value of heat of solution for SB block copolymer lies between the two values associated with the constituent homopolymers. Diffusion coefficients for gases in the block copolymer are bracketed by the homopolymer values over the range of temperature employed, but the activation energies for diffusion in SB are higher than either of the homopolymer values. The anomalous temperature dependence and the inability of a computer simulation to reproduce experimental diffusion coefficients supported the concept of a temperature-dependent restriction on chain mobility in the polybutadiene regions of the block copolymer. This β factor embodies the relative reduction in the rate of gas diffusion through the B regions of the copolymer compared to B homopolymer; β has a value of about 2-3 at room temperature but decreases to unity when the polystyrene chains become mobile at the polystyrene Tg.
    Additional Material: 3 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 31 (1986), S. 901-910 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The rotating bed plasma reactor described here permits uniform surface modification of relatively large amounts of powder materials. Scale-up to even larger batches of solids appears to be feasible. Some preliminary experimental data on the plasma surface modification of polymer powders have been presented. The results show that the flow rate, time of treatment, and type of feed gas are important operating parameters which influence the final surface character. One particular application of plasma-modified polymer powders was explored; by crosslinking and/or chemically modifying only the outermost surface regions of these powders, various polymeric materials may be rendered useful for use in thermal storage slurries. The major advantage of the surface-modified plasma treated powders over the bulk-modified powders used previously is the retention of essentially all of the pristine polymer heat of fusion in the surface-modified materials.
    Additional Material: 7 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 30 (1985), S. 1407-1418 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Liquid-phase sorption data are reported for the toluene-polyethylene system. The effects of fluorine plasma and inert-gas plasma treatments of the polymer surface were investigated. The presence of a fluorinated surface layer reduces initial solvent permeation rates, but the enhanced barrier property is lost when irreversible morphological changes occur during polymer swelling. A combination of chemical and morphological factors appears to be responsible for the observed temporary reduction in permeability; crosslinking of surface macromolecules was not a significant factor for the particular cases investigated in this work.
    Additional Material: 14 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 21 (1977), S. 629-643 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Engineering stress-strain properties were determined for two polystyrene-polybutadiene-polystyrene (SBS) triblock copolymer elastomers, one consisting of blocks of molecular weight 7000/43000/7000 and the other, 16000/85000/17000. In addition, various blends of these two materials were prepared in order to vary the number-average molecular weight of the blocks in a systematic way while maintaining polystyrene content in the range of 25-28 wt %. Samples were solvent cast from benzene or benzene/heptane mixtures and annealed before testing. Ring specimens were extended to rupture at varying strain rates on an Instron tensile tester. Results indicate that number-average molecular weight has a marked influence on stress-strain behavior over the range of molecular weights and testing conditions employed. The observed behavior is consistent with a systematic increase in the proportion of a mixed interfacial region between the pure polystyrene and polybutadiene domain as molecular weight decreases. The interfacial region contributes to mechanical hystersis, rate sensitivity, and toughness in the SBS materials. Scanning electron photomicrographs of fracture surfaces also showed systematic changes with molecular weight.
    Additional Material: 12 Ill.
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  • 8
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A high molecular weight polymer mixture was obtained from a sequential Ziegler-Natta polymerization of styrene and propylene. After removing unwanted homopolymers from the reaction product, the remaining copolymer was subjected to extensive molecular and morphological characterization. The results of these experiments indicate that the purified material is a diblock copolymer of isotactic polystyrene and isotactic polypropylene, with each block having a molecular weight in the range of 225,000 g/mol. This block copolymer was incorporated in varying amounts into blends of isotactic polystyrene and isotactic polypropylene homopolymers. At low concentrations of copolymer (〈20 wt %), the diblock functions as a dispersing agent, significantly reducing the size of domains in the heterogeneous blends. At higher copolymer concentrations, a dramatic improvement in the adhesion across the domain boundaries is also observed. The favorable effects of the copolymer on mechanical properties are demonstrated in the results of tensile impact experiments.
    Additional Material: 12 Ill.
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  • 9
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: This article proposes a temperature-jump (T-jump) approach for characterizing the kinetics of volume recovery in glassy materials. The kinetic characterization is based on the Kovacs-Aklonis model. This incorporates a retardation-time spectrum which shifts according to both the temperature and the instantaneous volume. The proposed experiments involve measuring the change in recovery rate caused by an abrupt temperature jump. Although an analogous procedure has been used to determine the activation energy for linear viscoelastic creep, the analysis for volume recovery is complicated by its inherent nonlinearity. Nevertheless, accounting for the nonlinearity by a reduction of the time scale permits the T-jump results to be analyzed. In particular, the T-jump approach can be used to: (i) test a particular functional form for the shift factor and (ii) determine the previously unmeasurable parameter x, which defines the relative importance of the temperature dependence and the volume dependence in this function. In addition, numerical simulations indicate that the proposed method can be implemented in the laboratory.
    Additional Material: 7 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1891-1901 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A nonisothermal creep experiment has been analyzed to ascertain its suitability for determining the temperature dependence of low activation energy viscoelastic processes in elastomers far above Tg. The nonisothermal method was employed to determine the activation energy for creep near 35°C in a lightly crosslinked cis-1,4 polybutadiene elastomer at small strains within the linear viscoelastic region, and at various large deformations up to rupture. The observed activation energy was essentially independent of the level of strain, and the value of ΔHa (∼11 kcal/mole) determined via the nonisothermal creep method was in good agreement with the result (∼12 kcal/mole) obtained via time-temperature superposition of isothermal linear viscoelastic creep data. The nonisothermal data allowed for an estimate of the volume of the “flow unit” associated with the controlling viscoelastic creep mechanism, attributed here to slippage of entanglements within the lightly crosslinked network.
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