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  • 1
    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: Infrared spectroscopy has been used to provide an independent estimate of dipole orientation in poled films of a side-chain polymer based on poly(methyl methacrylate) with an oxynitrostilbene side group attached via an aliphatic spacer. In particular, we used the dichroism of the absorption band assigned to the NO2 symmetric stretching vibration as a measure of the orientation of the nitrostilbene group. This yields 〈P2(cos θ)〉, where θ is the angle between the transition dipole moment and the symmetry axis of the sample. We then used a Langevin-type model to calculate 〈cos θ〉 from 〈P2(cos θ)〉 and concluded that values of 〈cos θ〉 as high as 0.5 are being achieved. We find, however, that 〈P2(cos θ)〉 obtained by comparison of normal incidence measurements on unpoled and poled films does not agree with 〈P2(cos θ)〉 obtained from tilted-film measurements on poled films. We propose that this discrepancy arises because the local field in a poled sample affects the polarizability of the molecules. To confirm this, we applied high fields to unpoled films in the infrared spectrometer at room temperature. The results clearly show a large reduction in absorbance with the applied field when the infrared electric field vector has a component perpendicular to the plane of the film. A major error therefore occurs as a consequence of the internal field in poled samples if 〈P2(cos θ)〉 is derived from the tilted film measurements, whereas 〈P2(cos θ)〉 derived from normal incidence measurements is essentially correct. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0887-6266
    Keywords: tensile drawing ; morphology ; polybutylene ; terephthalate ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The concept of the drawing of a molecular network has been employed to derive a total network draw ratio from the combination of the two deformations occurring in the production of poly(butylene terephthalate), PBT, fibers by the consecutive processes of melt spinning and cold drawing. The mechanical properties of PBT can then be more readily explained in terms of increases in this total network draw ratio. However, the preorientation and crystallization that occurs in the melt-spinning process can occur at different strain rates and temperatures, depending on the wind up speed employed, on the extensional viscosity of the polymer, and on the variation of the extensional viscosity with temperature. Therefore, for polymers such as poly(butylene terephthalate), which can exist in two crystalline forms, the morphology of the final drawn fiber might be expected to depend on the first melt-spinning stage of the process as well as on the total network draw ratio. In this work, density, birefringence, mechanical measurements, and WAXD measurements, which have been made on the melt-spun fibers and on the drawn fibers, are described. Small differences in some of the drawn yarn mechanical properties at the same overall network draw ratio are related to the crystallinity and in particular to differences in the proportion of the α and β phases present in the drawn yarn. These in turn are related to differences in the temperature and stress during melt spinning and drawing. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2465-2481, 1997
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
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