A two-dimensional IR correlation spectroscopic study of the conformational changes in syndiotactic polypropylene during crystallization

Abstract

The conformational changes of syndiotactic polypropylene (sPP) during melting and isothermal crystallization processes were studied by infrared (IR) and two-dimensional (2D) correlation analysis. The band at 963 cm−1 is assigned to the contribution of the amorphous component, and the band at 978 cm−1 is assigned to a shorter helical conformational length than the bands at 867 and 812 cm−1, which are related to crystalline helical conformation. The difference spectra and 2D correlation spectra analysis of the crystallization process indicated that the changes in these regular bands occur in rapid sequence, which is not easily detected by conventional IR spectroscopy. It was found that the absorption intensity of the band at 963 cm−1 increases earlier than that of the band at 978 cm−1, as well as of the bands at 867 and 812 cm−1. The results suggest that the partial chains among the amorphous component change in conformation first, then the sPP chains adjust their local conformations to form short helical conformations and finally crystallization occurs. Conformational changes of sPP during melting and isothermal crystallization process were studied by IR and 2D-correlation analysis. The absorption intensity of the band at 963 cm−1 (amorphous) increases earlier than that of the band at 978 cm−1 (shorter helix), and that of the band at 867 and 812cm−1 (crystalline helix). We found that partial sPP chains in amorphous component change their conformation first and then adjust their local conformations into short helix, and then crystallization occurs.