Multiple Peak Reference Method for Polarized Fourier Transform Infrared—Attenuated Total Reflection Spectroscopy to Determine the Three-Dimensional Orientation of a Uniaxially Drawn Poly(Trimethylene 2,6-Naphthalate) Film

Abstract

The polarized Fourier transform infrared-attenuated total reflection (FT-IR-ATR) technique is a very useful infrared spectroscopic method for characterizing the three-dimensional orientation of thick samples, to which the conventional transmission FT-IR method cannot easily be applied. To quantitatively analyze polarized FT-IR-ATR spectra, the dependence of the optical contact between the sample and the ATR crystal during the clamping and reclamping processes must be controlled. In this work, a new multiple peak reference (MPR) method is proposed and used to carry out a three-dimensional analysis of a poly(trimethylene 2,6-naphthalate) (PTN) polymer sample. The conventional single peak reference (SPR) analysis technique cannot be applied to such a sample due to the lack of an established reference peak. A new artificial reference band was generated by the MPR method using two different infrared bands, at 1602 cm⁻¹ and 917 cm⁻¹, in identical spectra with a combination constant of 0.95. The new artificial reference band was successfully used to calculate the three-dimensional orientation of various infrared bands of a uniaxially drawn PTN film, which has not previously been studied by three-dimensional orientation analyses using the polarized FT-IR-ATR method.