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  • Chemistry  (11)
  • NMR  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Predictive capabilities of a free-volume theory for solvent self-diffusion coefficients (1989)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 27 (1989), S. 1179-1184 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1989.090270517
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  • 2
    Electronic Resource
    Electronic Resource
    Influence of polydispersity and amine-epoxide ratio on molecular mobility in epoxy networks (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 29 (1991), S. 659-668 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Using nuclear magnetic resonance (NMR) T2 relaxation and pulsed-gradient spin-echo diffusion experiments at 175.5°C, molecular motions of the sole and gel of several epoxies of the type diglycidyl ether of bisphenol-A (DGEBA; Shell Epon 1007F and 1009F) cured with 4,4′-diaminodiphenyl sulfone (DDS) have been studies as a function of curative content. It was found that the fraction of protons associated with the shorter T2 component cannot be identified as the gel fraction until the substantial bimodal polymer polydispersity is accounted for in the spin relaxation model. The gel fraction and both relaxation rates have maxima near curing stoichiometry, and fall off more rapidly on the curative-poor side. The diffusion spectrum of the sol fraction was consistent with a light species (Epon 828 remnants) plus a polydisperse (M̄w/M̄n ≅2) heavier species, in agreement with resin and sol gel permeation chromatography (GPC) results. Numerical simulations also show that polymer polydispersity is likely to affect the interpretation of T2 relaxation found in the literature.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1991.090290603
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  • 3
    Electronic Resource
    Electronic Resource
    Molecular mobility in rubbery composites: Effect of filler particle size (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 1029-1039 
    Details
    ISSN: 0887-6266
    Keywords: rubbery composites ; molecular mobility ; polybutadiene ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We have measured proton NMR T2 relaxation spectra in Arco R45M OH-terminated poly-butadienes (PBs) cured with isophorone diisocyanate and filled with 65 wt % SiO2 particles of each of six different average sizes. Identifying the short T2 component with the gel, we find that the gel fraction is displaced from nominal NCO/OH stoichiometry, probably as a result of water adsorbed on filler particle surfaces. Near effective stoichiometry and in the presence of filler, molecular and segmental mobilities decrease, most strongly in specimens with the smallest filler particles. Comparison with parallel Monte Carlo simulations of the PB matrix geometry indicates that segmental mobility and sol migration decrease uniformly in a wide vicinity of the filler particles. Thus the rigidification of the matrix measured via NMR has a range of approximately 1-3 μm from nearby filler particle surfaces, representing the rms diffusion distance of the light components of the sol during the T2 relaxation. © 1993 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1993.090310813
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  • 4
    Electronic Resource
    Electronic Resource
    Syneresis and crystallinity in plasticized rubbery networks and compositesSupported in part by Thiokol Corporation. (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 1339-1349 
    Details
    ISSN: 0887-6266
    Keywords: rubber crystallinity ; plasticizers ; syneresis ; NMR ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We prepared polycaprolactone networks plasticized (60 wt%) with triacetin, with and without filler particles to model high-energy solid rocket propellants. Under strain and at lower temperatures these materials partially crystallize but also undesirably exude plasticizer (syneresis). We measured both properties isothermally (30°C) on the basis of molecular mobility: crystallinity with rapid-passage cw proton nuclear magnetic resonance (NMR), and syneresis with pulsed-gradient spin-echo NMR diffusion techniques, as a function of strain and time. In the gumstocks crystallinity and syneresis increase monotonically with strain and asymptotically with time. In a given specimen syneresis lags behind crystallinity but they approach the same value, suggesting that syneresis originates in expulsion of plasticizer from crystallizing regions. In the composites, crystallinity results resemble those in gum, but our diffusion data suggest that most syneresis is internal, with plasticizer accumulating in strain-debonded void regions near filler particles. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1994.090320805
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  • 5
    Electronic Resource
    Electronic Resource
    The effects of polydispersity, entanglements, and crosslinks on pulsed-gradient NMR diffusion experiments in polymer melts (1987)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 25 (1987), S. 1439-1457 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We have used the pulsed-gradient spin-echo NMR method to measure diffusion in a highly polydisperse polymer, a hydroxyl-terminated polybutadiene. We have modelled the expected spin-echo attenuation assuming that the low-molecular-weight fractions are unentangled and constitute a Rouse-like diluent to the entangled larger molecules. Fitting this simulation to our data is consistent with the model and permits the extraction of the range of diffusivities and a semiquantitative value for the molecular weight above which entanglements inhibit diffusion. The model is extended to include a monodisperse diluent present additionally, e.g., a curing agent. This extension is tentatively applied to polybutadiene resins undergoing curing and shows that the diffusivity of the remaining unreacted curing agent is little affected by network formation, whereas the retardation of the unreacted polymer molecules is clearly evident.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1987.090250707
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  • 6
    Electronic Resource
    Electronic Resource
    Network fraction and molecular motions in polymer composites: An NMR relaxation and self-diffusion study (1989)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 27 (1989), S. 503-522 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We have used NMR T2 relaxation and pulsed-gradient spin-echo diffusion techniques to study properties of Arco R45M hydroxyl-terminated polybutadiene, either unfilled or containing 65 wt.% filler particles (SiO2, NaCl, Al) and cured with isophorone diisocyanate (IPDI), as functions of IPDI content. A short T2 relaxation component arises from the network (gel) whose amount is greatest (up to 92%) near NCO/OH stoichiometry. Gel fraction and stoichiometry concentration both are affected slightly by filler surface reactivity but principally by filler particle size. The diffusion rate of the nonnetwork (sol) molecules has a range of 1-2 orders of magnitude. This range is narrowest near stoichiometry for the smallest filler (SiO2), i.e., the situation in which the sol molecules are least mobile. Branching theory and the hypothesis of a layer of reduced mobility in a wide vicinity of the filler particles provides semiquantitative explanations of these observations.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1989.090270303
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  • 7
    Electronic Resource
    Electronic Resource
    NMR relaxation study of thermal degradation in cured PMR polyimidesWork supported in part by NASA under grant NCC-3-164. (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 1545-1557 
    Details
    ISSN: 0887-6266
    Keywords: NMR relaxation ; PMR polyimides ; thermal degradation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We have studied cross-linking and thermal degradation of high-performance first-and second-generation PMR-15 polyimides, both thermoset and thermoplastic versions, by performing nonspectroscopic NMR solid echo T*2 relaxation measurements at temperatures up to 430°C using probes built for this purpose. We employ signal averaging and automated decomposition of the relaxation decays into two Gaussian components, the slower of which gradually appears above 300°C. Tracking the molecular mobility spectrum in terms of the relative intensity of the components and their relaxation times as temperature is cycled, we detect essentially no irreversible effects below the glass transition, measure permanent mobility reductions attributable to completion of cure, and find that exposure to temperatures above 380°C on the order of 1 h is required for substantial thermal degradation to occur. These results are closely supported by thermal and mechanical measurements on parallel specimens. Second-generation PMR resins appear to have higher microscopic rigidity and reduced viscous fraction at high temperatures. ©1995 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1995.090331012
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  • 8
    Electronic Resource
    Electronic Resource
    Use of carbon fibril additives to reduce the dc resistivity of elastomer-based composites (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 55 (1995), S. 935-943 
    Details
    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: We have prepared insert model solid rocket propellants of two kinds, polycaprolactone (PCP) networks highly (60%) plasticized with triacetin and hydroxyl-terminated polybutadiene (HTPB) cross-linked with isophorone diisocyanate, both filled with over 65% NaSO4 and Al powders as well as traces of fine carbon fibrils 100 Å thick and several micrometers long. Sheets of these dieletric composites were used for dc surface and volume electrical resistivities near room temperature. Addition of less than 1% fibrils in the PCP composites reduces volume resistivity by a factor of 10. The amount required for HTPB is only 0.1% leaving processability unaffected; resistivity reduction rises from one to nearly four orders of magnitude as potential differnce in increased from 10 to 500 V. Addition of fibrils to HTPB composites is a promising candidate for minimizing the incidence of dangerous electric discharge events. © 1995 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1995.070550612
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  • 9
    Electronic Resource
    Electronic Resource
    Measurement of crystallization in stretched rubber by rapid-passage NMR (1977)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 21 (1977), S. 1489-1497 
    Details
    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: Continuous-wave rapid-passage proton NMR (30 MHz) was performed on lightly crosslinked natural cis-polyisoprene at elongations up to 720%, at temperatures between -100° and 100°C, and after delays of up to several weeks after stretch. A method of separating the spectra into a narrow and a wide component was developed and applied. The results are interpreted in terms of the effects of a glass transition and strain-induced crystallinity and are in general agreement with results by other methods. The degree of crystallinity is found to increase strongly with strain (from zero for unstretched samples to 31% at elongations of 720% at room temperature), to increase with time, reaching equilibirium most rapidly in the most highly strained samples, and to decrease approximately linearly with temperature above about 20°C.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1977.070210605
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  • 10
    Electronic Resource
    Electronic Resource
    Pulsed-field gradient NMR measurements of diffusion of oil in rubber (1979)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 23 (1979), S. 877-885 
    Details
    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 pulsed-gradient NMR method of Stejskal and Tanner was used to measure the diffusion of oil in synthetic cis-polyisoprene. The diffusion encounters no barriers with spacings at least up to several μm and generally displays free-volume behavior, obeying the WLF temperature dependence between -10°C and +130°C, and the Fujita-Doolittle concentration dependence between 10 and 90 vol-% oil.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1979.070230322
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