Atom transfer radical copolymerization of acrylonitrile/n-butyl acrylate:: Microstructure determination by two-dimensional nuclear magnetic resonance spectroscopy

Atom transfer radical polymerization conditions were optimized and standardized with different initiator and catalyst systems. Acrylonitrile/n-butyl acrylate copolymers were synthesized with 2-bromopropionitrile as the initiator and CuCl/ CU(0)/2,2'-bipyridine as the catalyst system. Variations of the feed composition led to copolymers with different compositions. The number-average molecular weight and the polydispersity index were determined by gel permeation chromatography. Quantitative C-13{H-1} NMR was employed to determine the copolymer composition. The reactivity ratios calculated with a methodology based on the Mao-Huglin terminal model were r(A) = 1.30 and r(B) = 0.68 for acrylonitrile and n-butyl acrylate, respectively. The reactivity ratios determined by the modified Kelen-Tudos method were r(A) = 1.29 +/- 0.01 and r(B) = 0.67 +/- 0.01. C-13{H-1} NMR and distortionless enhancement by polarization transfer (DEPT-45, 90, and 135) were used to distinguish methyl, methylene, methine, and quaternary carbon resonance signals. The overlapping and broad signals of the copolymers were assigned completely to various compositional and configurational sequences by the correlation of one-dimensional (H-1, C-13{H-1}, and DEPT) and two-dimensional (heteronuclear single quantum coherence, total correlation spectroscopy, and heteronuclear multibond correlation) NMR spectral data. The complete spectral assignments of carbonyl and nitrile carbons were performed with the help of heteronuclear multibond correlation spectra. (c) 2005 Wiley Periodicals, Inc.