Normal Vibrations of the Polymer Molecules of Helical Conformation. V. Isotactic Polypropylene and Its Deuteroderivatives

Abstract

Polarized infrared spectra of isotactic polypropylene (IPP),[Complex chemical formula]were measured in the region from 4000 to 80 cm−1. The normal vibrations of these three polymers were calculated for the infrared‐ and Raman‐active A and E species, by the use of the GF‐matrix method with the Urey—Bradley force field. The results show a fairly good agreement between the observed and calculated frequencies. The assignments of the absorption bands were given, and discussions were made on the vibrational modes of the bands characteristic of the isotactic helical structures. A computation program for calculating the characteristic values and vectors of a Hermitian matrix was presented. From the normal coordinate treatment applied to the threo‐ and erythro‐ model of di‐isotactic polypropylene‐1‐d,[Complex chemical formula]it was found that the polymers prepared from trans‐ and cis‐propylene‐1‐d, CHD, CH–CH3, have threo‐ and erythro‐di‐isotactic structures, respectively, suggesting cis‐opening mechanism in the coordinated anionic polymerization [α‐TiCl3–Al(C2H5)3 catalyst]. The absorption bands characteristic of crystalline IPP are also observed in the 1:1 mole mixture of IPP and IPP‐1,1,2‐d 3, while these bands disappear in the copolymer with the same chemical composition. This fact shows that these characteristic bands arise from the intramolecular interactions in a helical molecule, and the sequence of a certain number of the same monomeric units in the helix is necessary for appearance of these bands. The 1152 and 975 cm−1 bands, which appear also in molten IPP and an ether‐soluble fraction of a commercial polypropylene, are ascribed to the chemical structure of head‐to‐tail sequence of –CH2–CH(CH3)– units.