Structure changes during the induction period of cold crystallization of isotactic polystyrene investigated by infrared and two-dimensional infrared correlation spectroscopy

The structural changes during the induction period of isotactic polystyrene (iPS) cold crystallization were investigated by using infrared (IR) spectroscopy together with 2D correlation analysis. It was found that the ordered orientation of the phenyl ring, local conformation change, and structural formation of 3(1) helix chain of iPS already appear during the induction period. Moreover, careful interpretation of the asynchronous 2D IR spectra generated from the time-dependent spectra enabled us to delineate the structural evolution during the induction period of iPS cold crystallization: Prior to the crystallization of iPS, the amorphous phase changes first, and then the ordering of the phenyl rings of iPS takes place. After that, the polymer chains adjust their local conformations to form the short 3(1) helix structure. The present study has also demonstrated that the generalized 2D IR correlation spectroscopy is powerful in studying small spectral changes in the induction period of polymer crystallization.