Abstract
ABSTRACT: The anisotropic scattering properties of a uniaxially oriented filament of an ethylene-tetra- fluoroethylene (E-TFE) alternating copolymer have been investigated in order to determine the molecular conformation in ordered crystalline regions. Both a trans-planar and a 312-helical structure have been shown to be energetically possible in an isolated molecule and in this study the group theoretical analyses for these structures are presented. Comparison of these results with polarized Raman measurements indicates that the copolymer backbone crystallizes in predominantly a planar-zigzag structure. Observation of the low-frequency Raman-active longitudinal acoustical mode (LAM) and the correlation of its frequency position with the crystalline stem length obtained from SAXS and crystallinity measurements strongly support the trans-planar structure. Introduction Studies of molecular orientation in polymers can be useful in determining the conformational, crystal, and morphological structure'-' as well as in determining cor- relations between these microscopic structures and ma- croscopic properties. In highly oriented polymers the structural symmetry of the chain and crystal will give rise to spectroscopic selection rules that govern spectral activity in both the infrared and Raman spectrum. When several conformational or crystal structures have been proposed by other methods it is often possible
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