Polymers orientational measurements

Although it would be possible in principle to choose any set of orthogonal axes in the structural unit to define Ox,x2x3, it is implicit in the discussion of orientation in polymers that the structural unit also has at least orthorhombic symmetry (Point group D2) with regard to the development of orientation. As can be appreciated this can lead to an element of awkwardness in dealing with the results of orientation measurements, because the molecular situation is often more complicated. 

A good applications-oriented measure of the use temperature for a ma-teral is the heat distortion or heat deflection test (HDT). The HDT is described by ASTM-D648 as the temperature at which a sample of defined dimensions (5 X Vi X Vs (or Va) in.) deflects under a flexural load of 66 or 264 psi placed at its center. In case of a largely amorphous polymer, the HDT temperature is typically slightly (10 to 20 °C) lower than the Tg as determined by DSC or DTA, whereas with more-crystalline polymers, it more closely correlates with the Tm. The HDT temperature is a useful indicator of the temperature limits for structural (load-supporting) applications. A loaded cantilever beam is used in another heat deflection test called the Martens method. 

The surface forces technique measures the force between molecules (eg. surfactants, polymers) adsorbed on mica sheets. In the case of large molecules such as polymers, the measurement is most sensitive to the regions closest to the solution and provides little direct information about the region adjacent to the surface. As it is a measurement between macroscopic surfaces, it is unable to provide information on microscopic chemical differences at the interface. Infrared spectroscopy could provide additional information about the quantity of adsorbed material on the mica surface, the identity and orientation of the adsorbed species, and possibly the nature of the surface linkage. 

Measurements of optical birefringence and density were obtained in an attempt to determine if total polymer orientation and the amount of fiber crystallinity would correlate with aging behavior. These values are presented in Table III. Because the secondary wall of cotton comprises... 

High birefringence An/g in solutions of aromatic polymers facilitates measurements of orientation angles a. Moreover, since the molecular weights of these polymers are usually low, the measured values of oi differ only by several degrees from ir/4 and the dependence of a on g in this... 

For a better understanding of infrared spectroscopy and its application to polymers and orientation measurements the reference of Zbinden (86) is suggested. 

In summary it should be apparent that many techniques exist for measuring molecular orientation in polymeric solids. These techniques, however, differ in many ways and in degree of sophistication as well. It should also be clear that the orientation measured by one technique may in fact not be what actually is desired e.g., separate orientation of the components in a multicomponent system may be desired yet certain techniques only allow an overall average orientation to be measured. This problem can be overcome as discussed by use of a combination of the techniques described. In fact, a multitechnique approach to an orientation problem is generally preferred in order to avoid inaccuracies of interpretation. Such an approach is indeed costly for the unequipped laboratory and hence selection must be made based on the information available on the polymer under investigation. 

Zbinden, R. Orientation measurements. Infrared spectroscopy of high polymers. Chap. V. New York Academic Press 1964. 

The subsequent study was oriented at the theoretical explanation of the factors that cause and affect zone spreading in TFFF [31]. Contributions of non-equilibrium and polydispersity of polymer samples under study to the total peak width were studied, as was the possibility of determining the precise polydispersity of the polymer by measuring peak width at various linear velocities of the solvent, and by extrapolating to zero velocity, i.e., by eliminating the contribution of non-equilibrium processes [32]. An improved separation in TFFF can be obtained by using... 

I. M. Ward (ed.), Structure and Properties of Oriented Polymers, Halsted Press, New York, 1975. B. Jasse and J. L. Koenig, Orientational measurements in polymers using vibrational spectroscopy, 7. Macromol. Sci. Revs. Macromol. Chem.) C17, 61 (1979). 

Measuring Polymer Orientation with IR and Raman Spectroscopy... 

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

An electric or magnetic field can orient the polymer, and measurement of this process gives information on the rotational motion of polymers in solution. Using the Smoluchowski equation, we shall consider the orientation caused by an electric field. 

Orientational Measurements in Polymers Using Infrared Dichroism... 

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