Molecular Vibrations and Structures of High Polymers. V The Infrared Active Normal Vibrations of Isotactic Polypropylene, Poly(propylene-2-d), Poly(propylene-1,1-d2) and Poly(propylene-3,3,3-d3) in the 1500∼650 cm−1 Region

The infrared active normal vibrations of isotactic polypropylene and its deuterated derivatives in the crystalline state have been treated by the general method derived previously. The modified Urey-Bradley force field has been used; the trans- and gauchecoupling potential terms for the H–C–C angles and the angle-interaction terms for the methylene group have been added to the Urey-Bradley force field. A total of 16 potential constants have been adjusted by the method of least squares, and a total of about 100 infrared-active frequencies have been calculated with the r.m.s. frequency deviation as small as 1.1%. The potential energy distributions have been calculated, together with the normal modes, and the nature of the inferred bands observed in the 1500∼650 cm−1 region have been elucidated. Vibrational assignments for the well-defined liquid bands of isotactic polypropylene and its deuterated derivatives have also been made.