Dichroism, polymer orientation

Ultraviolet dichroism has been applied to polymer orientation studies [11,12]. Quantitative analysis of the amount of conjugated unsaturated structure in rubbers can also be determined from ultraviolet and spectroscopic data. Conjugated systems such as polyenes or aromatics... 

Several sources of error may influence the calculations of chain orientation carried with the use of data from infrared dichroism experiments. Three specific problems are the improper treatment of chain conformation, the imperfect polariser behaviour, and the inaccurate assumptions regarding the value of the angle between a particular infrared-active transition moment and the polymer chain axis. In this paper, a quantitative analysis is presented of the magnitudes of these errors for several infrared bands commonly employed to characterise polymer orientation via infrared dichroism. 52 refs. 

Another standard method of measuring polymer orientation is infrared dichroism, which refers to the ratio of the IR absorption for light having... 

As the CSLM (see Section 6.2.1) uses an optical laser as its illumination source, it is relatively straightforward to attach a Raman spectrometer to its output to give a confocal Raman microscope. This further limits the region being analyzed and can produce optical sections and 3D images of chemical groups [316, 317]. Dichroism in a confocal Raman microscope has been used to measure polymer orientation in films [318, 319] and fibers [320]. 

Thus, the process of PAN transformation under the effect of IR radiation proceeds with considerable self-acceleration. The irradiation of uniaxially oriented PAN films gives a polymer with a distinct anisotropy of optical properties, dichroism in the visible spectral region in particular. Figure 8 presents dichroism curves [D =/(X)] at various angles (ip) between the polarization plane and the orientation axis. The same figure shows the dependence D =f(uniaxially oriented film. 

We now report that in the region of the absorption band the flow linear dichroism of a solution of 1 is positive (Fig. 3). Assuming that the nature of the flow orientation is of the usual kind, i.e., that the polymer chains in a random coil conformation which dominates in solution (34) tend to align with the flow direction, this observation provides additional support for the absolute assignment of the transition moment direction along the chain direction, even in solution. Similar conclusions based on polarization studies on a stretched film of poly(di-n-hexyl silane) have recently been reported (36). 

IR dichroism is another useful technique for assessing chain orientation." In a uniaxial ly deformed polymer sample, there is assumed to be rotational symmetry about the draw direction, in which case the orientation of a chain molecule is... 

Infra-red dichroism has been used in studies of polymer specimens in which the chain molecules are parallel to each other, to give evidence on the orientation of particular atomic groups. In nylon and polyvinyl alcohol (Ambrose, Elliott, and Temple, 1949), Terylene (Miller and Willis, 1953), and polytetrafluoroethylene (Liang and Krimm, 1956) the results are consistent with structures already established by X-ray methods. Turning to more complex structures not yet solved in detail by X-ray methods, infra-red dichroism has indicated that in cellulose... 

The first example to appear on dichroism in the Raman spectrum of oriented polymers concerned fibres and films of isotactic polypropylene (17). Unfortunately it was not possible to interpret the results because... 

In contrast to n-n transitions, the n-n transitions of heterocyclic compounds and carbonyl-containing rings are often polarized in a direction perpendicular to the plane of the ring. Linear dichroism of cytosine, adenine, and other nucleic acid bases has been measured on single crystals and in partially oriented polymer films.71 Magnetically induced linear dichroism provides a new tool for study of metalloproteins.72... 

Several attempts to induce orientation by mechanical treatment have been reviewed 6). Trans-polyacetylene is not easily drawn but the m-rich material can be drawn to a draw ratio of above 3, with an increase in density to about 70% of the close-packed value. More recently Lugli et al. 377) reported a version of Shirakawa polyacetylene which can be drawn to a draw ratio of up to 8. The initial polymer is a m-rich material produced on a Ti-based catalyst of undisclosed composition and having an initial density of 0.9 g cm-3. On stretching, the density rises to 1.1 g cm-3 and optical and ir measurements show very high levels of dichroism. The (110) X-ray diffraction peak showed an azimuthal width of 11°. The unoriented material yields at 50 MPa while the oriented film breaks at a stress of 150 MPa. The oriented material, when iodine-doped, was 10 times as conductive (2000 S cm-1) as the unstretched film. By drawing polyacetylene as polymerized from solution in silicone oil, Basescu et al.15,16) were able to induce very high levels of orientation and a room temperature conductivity, after doping with iodine, of up to 1.5 x 10s S cm-1. 

Beer, M. Quantitative interpretation of infrared dichroism in partly oriented polymers. Proc. roy. Soc. A236, 136—140 (1956). 

Interpretation of infrared dichroism in axially oriented polymers. J. chem. Phys. 28, 1113—1115 (1958). 

An example of a relevant optical property is the birefringence of a deformed polymer network.256 This strain-induced birefringence can be used to characterize segmental orientation, and both Gaussian and non-Gaussian elasticity.92,296-302 Infrared dichroism has also been particularly helpful in this regard.82,303 In the case of the crystallizable polysiloxane elastomers, this orientation is of critical importance with regard to strain-induced crystallization, and the tremendous reinforcement it provides.82... 

A second class of polarizers uses dichroism to produce linearly polarized light. Techniques to produce dichroic polarizing sheets were pioneered by Land [52], These are made by dissolving a strongly dichroic, small molecule into an amorphous, transparent polymer. The dichroic molecules are then oriented by a uniaxial stretching of the polymer matrix. Since this is accomplished below the polymers glass transition temperature, this ori-... 

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