Molecular Vibration and Structure of High Polymers. IV. A General Method of Treating Degenerate Normal Vibrations of Helical Polymers and Infrared-Active Vibrations of Isotactic Polypropylene

Abstract

Polarized infrared spectra of an oriented crystalline film of isotactic polypropylene have been measured in the region 600–300 cm—1. Two parallel bands and three perpendicular bands due to the skeletal deformation modes have been observed. A general method for treating the normal vibrations (with any given phase difference) of infinite helical chain polymers has been restudied. The method has been applied to the infrared active normal vibrations, A and E(⅔π), of isotactic polypropylene. The modified Urey—Bradley force field has been used and the potential constants have been transferred from aliphatic hydrocarbons. The calculated frequencies and potential energy distributions have been used as aids in assigning the infrared bands of isotactic polypropylene in the region 1500–300 cm—1.