Characterization of brominated natural rubber by solution-state 2D NMR spectroscopy

• Published in: Reactive & functional polymers Vol. 113; pp. 6 - 12
• Main Authors: Choothong, Nuorn, Kosugi, Kenichiro, Yamamoto, Yoshimasa, Kawahara, Seiichi
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.04.2017; Elsevier BV
• Subjects: Brominated natural rubber; Bromination; Carbon; Dichloromethane; Isomerization; Isoprene; Magnetic resonance; N-bromosuccinimide; Natural rubber; Nitrogen; NMR spectroscopy; Rubber; Solution-state 2D-NMR measurement; Spectrum analysis; Brominated natural rubber; Solution-state 2D-NMR measurement; N-bromosuccinimide
• ISSN: 1381-5148; 1873-166X
• DOI: 10.1016/j.reactfunctpolym.2017.02.004

Bromination of natural rubber was analyzed through nuclear magnetic resonance (NMR) spectroscopy, in which small 1H and 13C NMR signals, appearing after bromination of natural rubber, were positively assigned by 1D and 2D NMR measurements. The brominated natural rubber (BrDPNR) was prepared by bromination of deproteinized natural rubber (DPNR) with N-bromosuccinimide (NBS) in dichloromethane at 303K for 3h under a nitrogen atmosphere. The 13C NMR signals at 20.5, 22, 29, 29.8, 35.8, 40 and 112.4ppm were assigned to the primary and the secondary carbons of the brominated trans-1,4-isoprene units, whereas the signals at 24.5 and 32.6ppm were assigned to the primary and the secondary carbons of the brominated cis-1,4-isoprene units. During the bromination of DPNR with NBS, the isoprene units underwent cis-trans isomerization. The bromination of natural rubber with NBS occurred after the hydrogen abstraction of cis-1,4-isoprene units. The reaction between the allylic carbon radicals and bromine radicals generate the brominated trans-1,4-isopren units. [Display omitted]