Simple methods for assessing the conformational sensitivity of infrared bands by dichroism

In characterizing the overall orientation of polymers by infrared (IR) dichroism, the orientation function must be obtained from the dichroic ratios of conformationally insensitive bands. Identification of such bands is thus necessary prior to the calculation of the orientation function. In this study, we devise two simple methods for evaluating the conformational sensitivities of IR bands from the measurement of the dichroic ratio. Both methods are based on the fact that the orientation function calculated by all conformationally insensitive bands should be identical, while this is not true for conformationally sensitive bands. Poly(ether ether ketone) (PEEK) is used as an example to demonstrate the use of these methods.