Stereochemical assignments of the nuclear magnetic resonance spectra of isobornyl acrylate/methacrylonitrile copolymers

摘要

Isobornyl acrylate (B)/methacrylonitrile (N) copolymers with different compositions were synthesized by the free-radical bulk polymerization with azobisisobutyronitrile as the initiator under a nitrogen atmosphere at 70°C. The copolymer compositions were calculated from quantitative 13C(1H)NMR spectra. The reactivity ratios of the comonomers in the B/N copolymers determined from the linear Kelen-Tudos method and nonlinear error-in-variable method were r _B = 0.66 ± 0.11 and r _N = 1.54 ± 0.22 and r _B = 0.74 and r _N = 1.65, respectively. The complete spectral assignments of the ~1H-NMR and ~(13)C(~1H)-NMR spectra were carried out with the help of distortionless enhancement by polarization transfer, two-dimensional (2D) heteronuclear single quantum coherence, and 2D total correlation spectroscopy. The nitrile carbon of the N unit and the methine and OCH carbons of the B unit were assigned to triad compositional sequences, whereas the β-methylene carbons of the B and N units were assigned to the tetrad compositional and configurational sequences. The α-methyl carbon of the N unit was also assigned to the triad level of configurational and compositional sequences. Similarly, the nitrile and quaternary carbon resonances with the methine, methylene, and methyl protons were studied in detail with 2D heteronuclear multiple-bond correlation spectra.