Vibrational dynamics and heat capacity in syndiotactic poly(propylene) form II

Normal modes and their dispersion are obtained for planar-zigzag form II (tttt) of syndiotactic polypropylene (sPP) in the reduced zone scheme using Urey-Bradley force field and Wilson's GF matrix method as modified by Higgs. It is observed that this all trans backbone conformation can be characteristized by a band at 1233 cm−1 (calculated at 1239 cm−1). A comparison is made with the spectra of its isotactic and helical form. Characteristic features of the dispersion curves such as crossing, repulsion and von Hove type singularities (regions of high density-of-states) have been explained. Heat capacity obtained from the density-of-states agrees with the experimental data up to 250 K at which the glass transition sets in and the experimental curve exhibits a marked change in slope.