Normal vibrational analysis of the syndiotactic polystyrene s(2/1)2 helix

The full vibrational spectra of the γ, δ and ε crystalline phases of syndiotactic polystyrene (_sPS), i.e., phases presenting the s(2/1)2 helical conformation, have been experimentally determined and compared with that calculated at the B3LYP/6-31G(d,p) level of theory for an infinite helix. The assignment of the different modes was highly facilitated and validated by the experimental evaluation of the direction of the transition moment vector of most IR peaks, which was made possible for the first time by measurements on sPS films with different uniplanar orientations of the crystalline phase. The normal vibration analysis of most representative modes of the periodic model allowed for a general description of each one to be obtained, which was further confirmed by the direct inspection of mode animations.