Transferability of valence force constants from “overlay” calculations: Molecular vibrations of syndiotactic 1,2-polybutadiene

The fundamental vibrational frequencies of syndiotactic 1,2-polybutadiene have been calculated. Valence force constants obtained from saturated hydrocarbons and from methyl derivatives of ethylene can be very satisfactorily transferred to this molecule. Accidental degeneracies between in- and out-of-phase motions of the two chemical units in the identity period have been found for some normal mode and their importance for the interpretation of the spectra of vinyl polymers is discussed.

It is shown that the analytical absorption band at 669 cm⁻¹ can be certainly taken as a characteristic “tacticity band”.