NMR Study on the Dissolved State of Polyacrylonitrile in Various Solvents

Abstract

ABSTRACT:An attempt was made to elucidate the dissolved state of polyacrylonitrile (PAN) in various solvents by analyzing 13 C NMR chemical shift difference for the arbitrarily chosen two NMR peaks derived from PAN molecules and by considering solvent effect on the electro-magnetical parameters introduced previously with aid of solvation phenomena of PAN in solvents. For this purpose, R-PAN andy-PAN employed hithetofore were subject to the analysis. Solvents employed included typical organic solvents such as dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), and aqueous (aq) inorganic solvents such as 70 wt% aq nitric acid (HN03), 55 wt% aq sodium thiocyanate (NaSCN). The dissolved state or the solvation state of PAN in organic solvent was mainly discussed in comparison with that in aq HN03, which is known most powerful solvent even for highly isotactic PAN. It was found that interaction of all solvents to polymer is strictly dependent on polymer stereoregularity and the solvent power is related to the solvent ability to interact on the long meso (m) sequence part in PAN. Aq HN03 shows quite different interaction form with nitrile group in mm and mr (r, racemo) sequences rather without forming n electron conjugate system. In contrast to this, the organic solvents proved to have individually favorable interaction sites more or less forming n electron conjugate system with nitrile group in polymer. The favorable polymer site was mmr for DMSO and mr for DMF and DMAc. Solvation number of solvent was proved to be in good accordance with that theoretical solvation number, calculated by assuming that each solvent solvates on its favorable sites in polymer. The tentative solvation form for each solvent is proposed.KEY WORDS Nuclear Magnetic Resonance I Polyacrylonitrile I Solvation I Dimethyl Sulfoxide I Dimethylformamide I Dimethylacetamide c I n Electron Conjugate System I Atactic polyacrylonitrile (PAN) is well known to dissolve into concentrated inorganic salt solution (for example, sodium thiocyanate (NaSCN)), concentrated inorganic acid solvents (aq nitric acid (HN0 3 ), sulfuric acid), and polar organic solvents such as N,N' -dimethylformamide (DMF), N,N'-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), and ethylene carbonate (EC). The concentrated solutions of PAN in these solvents have been extensively employed in the commercial production of acrylic fibers. 1 It is very true that structure and properties of commercial acrylic fibers differ from another to one another. Although we should bear in mind that the commercial acrylic fibers are not made from PAN homopolymer but from different copolymer types of PAN, one of important factors controlling the final properties and structures of acrylic fibers might be attributable to the difference in the solvent employed as far as the wet-spinning method is concerned. Recently, Kamide and his coworkers 2 -5 carried out a very detailed solution study on atactic PAN (R-PAN), synthesized by redox polymerization and highly isotactic PAN (y-PAN...

Study on the Stereoregularity of Polyacrylonitrile Produced by Precipitation Polymerization in Supercritical CO2

“…Due to the interaction of solvent to polymer is dependent on polymer stereoregularity and the solvent power is related to the solvent ability to interact on the long meso (m) sequence part in PAN, 18 the lower isotactic CO 2 -PAN means that it has good dissolve ability in solvent, which is proved by being dissolved in DMF easily for wet-spinning, the mentioned work was appeared in our another research paper. 8 …”

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