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  • 1
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 229-239 
    ISSN: 0887-624X
    Keywords: ammonia/ammonium thiocyanate solvent ; cellulose ; dissolution mechanism ; solid state CP/MAS 13C-NMR ; X-ray ; conformation ; hydrogen bonding ; ammonia mercerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ammonia/ammonium thiocyanate (NH3/NH4SCN) is an excellent swelling agent and solvent for cellulose, even at a high degree of polymerization. Because polymorphic conversion in cellulose has been a long-standing, perplexing, troublesome problem, we have undertaken to study that mechanism. Solid state CP/MAS 13C-NMR and X-ray analysis proved to be very useful analytical techniques for the task. It appears that during temperature cycling, specific cellulosic inter- and intramolecular hydrogen-bonds are broken as polymorphic conversion proceeds sequentially from the polymorph I to III, and finally at total solvation to amorphous. This proceeds correspondingly via transformation of the polymorph conformations of CH2OH from trans-gauche, “tg,” to gauche-trans, “gt,” to gauche-gauche, “gg.” © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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  • 2
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 2209-2222 
    ISSN: 0887-6266
    Keywords: poly(1-trimethylsilyl-1-propyne) ; poly(1-phenyl-1-propyne) ; blends ; gas and vapor transport ; NMR ; Maxwell model ; Bruggeman model ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Pure gas and hydrocarbon vapor transport properties of blends of two glassy, polyacetylene-based polymers, poly(1-trimethylsilyl-1-propyne) [PTMSP] and poly(1-phenyl-1-propyne) [PPP], have been determined. Solid-state CP/MAS NMR proton rotating frame relaxation times were determined in the pure polymers and the blends. NMR studies show that PTMSP and PPP form strongly phase-separated blends. The permeabilities of the pure polymers and each blend were determined with hydrogen, nitrogen, oxygen, carbon dioxide, and n-butane. PTMSP exhibits unusual gas and vapor transport properties which result from its extremely high free volume. PTMSP is more permeable to large organic vapors, such as n-butane, than to small, permanent gases, such as hydrogen. PPP exhibits gas permeation characteristics of conventional low free volume glassy polymers; PPP is more permeable to hydrogen than to n-butane. In PTMSP/PPP blends, both n-butane permeability and n-butane/hydrogen selectivity increase as the PTMSP content of the blends increases. © 1996 John Wiley & Sons, Inc.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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