~(13)C NMR AND INFRARED CHARACTERISTIC TACTICITY OF POLYACRYLONITRILE POLYMERIZED IN SUPERCRITICAL CO_2

摘要

With respect to the intense advantages in environmental friendly, low cost, and nonflammable alternatively to the aqueous and organic solvents, recently, the supercritical CO_2 has been broadly applied to make industrial polymers including the PAN. At present time, polymerization of acrylonitrile (AN) in the presence of CO_2 has been reported by some researchers. Of which, Shiho and DeSimone have carried out the dispersion polymerizatibn of acrylonitrile in carbon dioxide using a block copolymer as a stabilizer. They discussed the effects of reaction conditions on the resulting size of the PAN particles. In our lab, the precipitation polymerization of AN in supercritical CO_2 has also been successfully conducted. We discussed molecular weight and spinnability as well as molecular weight distribution of obtained PAN product. As an extension of the previous study, recently, the tacticity of PAN, prepared using AIBN as initiators by precipitation polymerization in supercritical CO_2 (hereafter, referred as CO_2-PAN) was investigated by ~(13)C NMR and IR method. We think the detailed analysis on tacticity of CO_2-PAN will be very helpful for a better understanding of CO_2-PAN's polymerization mechanism and its characteristics molecular properties in solution. In order to better understand the tacticity of CO_2-PAN (Mw=1.2x 10~5), in this paper, we tried to use the S-PAN (aqueous phase suspension polymerization, using AIBN as initiator, in radical mechanism, Mw=8.2 x 10~5) and R-PAN (using the redox type initiator in aqueous media, Mw=1.6x 10~5) for comparison. Notably, all the data for R-PAN is quoted from Kamide.