Two-Dimensional Correlation Analysis of Polyimide Films Using Attenuated Total Reflection-Based Dynamic Compression Modulation Step-Scan Fourier Transform Infrared Spectroscopy

Abstract

Attenuated total reflection (ATR)-based dynamic compression modulation two-dimensional (2D) correlation study of poly(p-phenylene biphenyltetracarboximide) film is carried out in combination with spectral simulation analysis by density functional theory (DFT). The dynamic 2D infrared (IR) correlation spectra in the region of imide I (C=O stretching mode) show three distinct correlation peaks located around 1777, 1725, and 1708 cm⁻¹. The band at 1708 cm⁻¹ is the lower wavenumber shift component of 1777 or 1735 cm⁻¹ peaks and is attributed to the results from intermolecular interactions, according to the DFT analysis. The 1708 cm⁻¹ band also shows the largest dynamic response, suggesting that these intermolecular interactions may enhance the dynamic response. The dynamic 2D IR correlation spectra in the region of imide II (C–N–C axial stretching mode) vibrations also show three correlation peaks located around 1335, 1355, and 1370 cm⁻¹, although the imide II band is shown to consist substantially of one component by the DFT analysis. These multiple peaks may be attributed to the compression-induced wavenumber shift of the band in the backbone structures. The sequential analysis of 2D correlation data show that, upon applying the dynamic compression, the response of the backbone regions (imide II) occurs first, followed by that of the side-chain regions (imide I, C=O).