Study on the Crystalline Structure Transition of Syndiotactic Polystyrene Film during Heat Treatment by Two-Dimensional Infrared Correlation Spectroscopy

Abstract

The crystal structure transition of syndiotactic polystyrene film from the helical conformation to the more stable planar zigzag conformation during a heating process was studied using Fourier transform infrared (FT-IR) spectroscopy in combination with two-dimensional (2D) correlation analysis and perturbation-correlation moving-window 2D analysis. The sequence of different conformations during the transition was investigated by analyzing two-dimensional FT-IR correlation spectra in the spectral ranges of 800–700 cm⁻ and 600–500 cm⁻¹. It was observed that the conformation of δ helical changes prior to γ helical, and the γ helical phase is faster than the α' planar zigzag phase. By utilizing the 2D asynchronous correlation spectra, the 744 cm⁻¹ band, which is usually incorporated in the broad 750 cm⁻¹ band, can now be uniquely attributed as the α' zigzag configuration for the first time. Furthermore, by employing thermal perturbation, the shorter helical segments consisting of m = 7–12 and m = 12–20 monomeric units were disturbed in a shorter time than the longer helical segments m = 20–30 during the heating process.