Identification of molecular vibrations associated with tacticity in polypropylene: Density functional theory‐based simulations

Abstract

The polymerization of vinyl monomers with achiral carbon center forms polymers with different spatial arrangements resulting in products with a different set of mechanical and thermal properties. Therefore, control of the tacticity (stereochemistry) is of major importance for controlling the polymer properties. It is possible to manipulate the polymer stereoregularity through the application of appropriate synthetic protocols. However, the polymers obtained using these protocols are not perfect, and thereby, it is essential to know the amount of different stereoregular units in a polymer mass. Generally, extensive NMR techniques and vibrational spectroscopy are used in this regard. To investigate further, a detailed DFT has been employed in this manuscript for syndio and isotactic polypropylene. The DFT allows generation of the vibrational spectra in the far‐infrared (0–400 cm−1) region, demonstrating the distinct nature of both types of polymers. The vibrational spectra for pure syndio and isotactic polypropylene as well as their conformer defects have been identified in this study. These studies of vibration spectra in the far‐infrared regime can be used to identify signatures of pure racemo and meso dyads along with the type of conformer defects present in pristine varieties. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1378–1385