Structural investigations of acrylonitrile–vinyl acid copolymers by NMR spectroscopy

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Abstract

1H, 13C [1H]-, and 2D HETCOR NMR spectroscopy have been employed to characterize polyacrylonitrile (PAN) homopolymer and copolymers of methacrylic acid (MAA) and itaconic acid (IA) prepared by solvent–water suspension polymerization technique in a mixture containing DMF (solvent) and water. The chemical composition of P(AN–MAA) copolymers was determined using 1H-NMR and that of P(AN–IA) using quantitative 13C[1H]-NMR spectra. P(AN–IA) copolymers show two separate signals due to two carboxylic groups in different magnetic environments of IA, whereas P(AN–MAA) shows only one in the region of δ 6.32–7.60 ppm in 1H-NMR and δ 171.0–176.0 ppm in 13C[1H]-NMR spectra. Evidence of acrylamide formation by the partial hydrolysis of AN groups is obtained by the small broad signal at δ 7.9 ppm in 1H-NMR spectra. No carboxylic proton signal was observed in copolymers containing 12 mol % of comonomer, which indicates the formation of anhydride. The microstructure was obtained in terms of the A- and M-centered triad sequences from 13C[1H]-and 1H-NMR spectra of the copolymers, which showed configurational and compositional sequences. For example, at higher comonomer content, the concentration of AAM and AAI sequencing increases. This is confirmed by 2D HETCOR NMR spectra also. The distribution of AN sequences is found to be random (n0nm ≃ 2.0). The tacticity values are not affected by the comonomer content. The isotacticity remained almost same at 27% (mm, 26.5–29.3) in all acrylonitrile polymers irrespective of the nature of the comonomer and polymerization medium, that is, DMF/H2O ratio. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1211–1217, 2003

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