| Abstract: | The high-resolution NMR spectra of polyacrylonitrile-β,β-d2 prepared by radical polymerization were determined, and the stereoregularity of the polymer was studied. The NMR spectra of methine protons of polyacrylonitrile-β,β-d2 in dimethyl sulfoxide-d6 and a mixture of nitromethane-d3 and ethylene carbonate showed three partially resolved multiplets. The deuterium-decoupled spectra of the polymer were measured, and three well resolved peaks were observed in the two solvents and dimethylformamide-d7. These three peaks were analyzed by comparison with the NMR spectra of model compounds and polyacrylonitrile-α-d, and they were assigned to isotactic, heterotactic, and syndiotactic triads with decreasing magnetic field. This order seems to be unchanged in other solvents. Triad stereoregularity of the polymer was determined according to the assignment. Polymerizations of acrylonitrile-β,β-d2 by radical initiators between ?78°C and 60°C were explained by the Bernoulli trial propagation step. The polymers had an atactic structure, independent of polymerization temperature. This shows that in free-radical polymerization of acrylonitrile, the chain end is not represented as having any particular stereochemistry. Other stereochemical control is necessary to produce tactic polymers. The triad tacticity of isotactic polyacrylonitrile was also determined. |
