Observation of pentads in deuterated polyacrylonitrile by NMR spectroscopy

Abstract

The deuterium‐decoupled methine proton spectra of polyacrylonitrile‐β,β‐d₂ were measured at 156°C in dimethylsulfoxide‐d₆ solution. Splittings of triad peaks caused by pentad sequences were observed. The isotactic triad resonance was resolved into three peaks and the heterotactic resonance into two peaks, while the syndiotactic resonance was unresolved or resolved into three peaks. The splittings were assigned by comparing the probability of each pentad sequence with observed intensities. The pentad signal shifted to the higher magnetic field with increasing number of meso configurations as neighbors of the central triad. It was observed that the pentad of atactic polyacrylonitrile‐β,β‐d₂ obeyed Bernoullian statistics but that of isotactic polymer obtained by γ‐ray irradiation of the canal complex seemingly obeyed first‐order Markov statistics.