Infrared linear dichroism has been a useful tool for studying the conformation and orientation of polymer molecules in deformed samples. When a polymer film is drawn, the macromolecular chains tend to align in a specific direction. The oriented film may then absorb, to different extents, incident infrared radiation polarized parallel and perpendicular to a reference direction usually defined as the draw direction. When a sample film absorbs more parallel than perpendicular light, the dichroic difference, Δ<i>A</i> = <i>A</i><sub>∥</sub> − <i>A</i><sub>⊥</sub>, is positive and the dichroic ratio, <i>R</i> =<i>A</i><sub>∥</sub>/<i>A</i><sub>⊥</sub>, is greater than one. The dichroic ratio has traditionally been used to aid in the assigning of infrared bands to specific vibrational modes and to help determine the molecular chain orientation.

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