Infrared absorption spectra of polyacrylonitrile and deuterated polyacrylonitriles

Poly-α-deuteroacrylonitrile and poly-α,β,β-trideuteroacrylonitrile were synthesized. α-Deuteroacrylonitrile was prepared by the deuterium exchange reaction of acrylonitrile with D2O in the presence of CaO. α,β,β-Trideuteroacrylonitrile was prepared by the addition reaction of C2D2 and DCN. The infrared spectra of polyacrylonitrile, the deuterated polyacrylonitriles, and the intermediate products of the syntheses were measured in the 4000–400 cm.-1 region and discussed. The polarized spectra of the oriented polymer samples were also measured. The bands of PAN in the CH stretching region exhibit reasonable shifts in the spectra of the deuterated polymers, while the C≡N stretching band shows no appreciable shift. The bands in the region lower than 1400 cm.-1 exhibit complicated behavior in deuteration. The calculation of the normal vibrations of polyacrylonitrile has been made, assuming a syndiotactic planar zigzag chain as a most simple model for calculation. The assignments of the bands are discussed.