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  • 1
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The activity of a solid, polymer-supported catalyst (a semicrystalline polyethylene film containing grafted, sulfonated styrene) was shown to be altered by cold drawing. The catalytic activity was measured by a test reaction, the dehydration of isopropyl alcohol to give propylene. Catalytic reaction rates were measured with variously drawn films clamped in a differential flow reactor operated at 100°C and 1 atm. The catalytic activity increased with the elongation of the polymer up to a draw ratio of 2.5; the activity decreased upon further drawing. The drawn films were characterized by x-ray diffraction, dynamic mechanical measurements, electron microscopy, birefringence, and density measurements. Since no evidence was found for the formation of surface sites by creation of microcracks, the changes in activity are attributed to modifications in the polymer structure induced by drawing. The kinetics of the catalytic reaction and the data giving percentage crystallinity and crystalline and amorphous orientation factors suggest that, in the undrawn polymer, the catalytically active —SO3H groups form a hydrogen-bonded network, which is excluded from the crystalline regions. Initial elongation partially breaks up the network, allowing more —SO3H groups to bond to alcohol and become catalytically engaged. Elongation beyond a draw ratio of 2.5 leads to a separation of —SO3H groups greater than that required for the formation of the reaction intermediate, which involves the alcohol hydrogen bonded to several —SO3H groups. The combined results of the catalytic kinetics experiments and structural characterizations imply that the preliminary deformation response of the semicrystalline polymer occurs predominantly within the noncrystalline regions and is accommodated by the rigid slip and tilting of crystal lamellae. The hydrogen bonding among the —SO3H groups in the noncrystalline regions hinders lamellar breakup and suppresses the formation of highly aligned fibrillar morphologies.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Nylon-based membranes of greater dialyzing capacity than Cuprophan have been prepared by solution casting. Good permeability is being achieved by the use of diluents such as dimethylsulfoxide in the casting solution. Modifying resins, primarily epoxies, contribute to higher permeability, good aging stability, and heat-sealing properties. Drying time between film casting and water immersion as well as the temperature and composition of the immersion bath are important factors in membrane performance. Methods for attaching heparin to the film surface have been developed, thus imparting good blood compatibility to the membranes.
    Additional Material: 1 Ill.
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  • 3
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A major part of current effort in improving artificial hemodialysis techniques concerns the development of improved membrane structures. Although blood compatibility of membranes is a part of the Battelle program, this discussion is confined to membrane composition, structure, and transport. On the basis of a need for improved hemodialysis techniques, membranes for use in the artificial kidney were prepared and evaluated for urea, creatinine, and uric acid permeability. Water-soluble polymers were crosslinked to form insoluble, but swellable, membranes. Faster metabolic waste transfer than with the conventional cellulosic membranes was obtained with diisocyanate-crosslinked poly (vinyl pyrrolidone) and poly (vinyl pyrrolidone)-dextran membranes and with membranes obtained by crosslinking poly (vinyl alcohol) with polyfunctional aldehydes. Membranes prepared from emulsions of vinyl pyrrolidone-ethyl acrylate and vinyl pyrrolidone-styrene copolymers had exceptionally high urea and creatinine dialysis rates, but were deficient in uric acid transfer. This shortcoming was corrected by incorporating solutes such as sucrose into the membranes followed by leaching. Another important approach concerned the development of a relatively high-strength membrane based on an impermeable nylon resin. Permeability of these membranes which have dialysis characteristics superior to those currently used was obtained through the addition of DMSO and one of several other additives to the coating solution.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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