The stereoregularity of polyacrylonitrile and its dependence on polymerization temperature

The stereoregularity of polyacrylonitrile was studied by NMR spectroscopy. The methylene protons in isotactic configuration are equivalent in dimethylformamide‐d7 solution and are nonequivalent in dimethylsulfoxide‐d6 solution. In the case of the latter solution the difference in chemical shift between the isotactic methylene protons is 6.6 cps. The stereoregularity of polyacrylonitrile‐α‐d instead of polyacrylonitrile was determined on the dimethylformamide‐d7 solution. In the radical polymerization all the polyacrylonitrile‐α‐d's that polymerized at temperatures between 80 and −78°C. have a configuration consisting of about 50% of isotactic diads and, accordingly, the stereoregularity of polyacrylonitrile does not depend upon the polymerization temperature. Analysis of the NMR spectra of isotactic polyacrylonitrile prepared from acrylonitrile–urea canal complex was also carried out. The NMR spectra of meso‐ and dl‐2,4‐dicyanopentanes, dimer models of isotactic and syndiotactic polyacrylonitriles, respectively, were analyzed by a computer program proposed by Bothner‐By.