Characterization of Brominated Natural Rubber By Solution State 2D NMR Spectroscopy

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 one-dimentional (1D) and two-dimentional (2D) NMR measurements. The BrDPNR was prepared by bromination of deprotenized natural rubber (DPNR) with N-bromosuccinimide (NBS) in dichloromethane solution at 303K for 3 hours under nitrogen atmosphere. The ¹³C-NMR signals at 20.5, 22, 29, 29.8, 35.8, 40 and 112.4 ppm were assigned to primary and secondary carbons of brominated trans-1,4-isoprene units, whereas the signals at 24.5 and 32.6 ppm were assigned to primary and secondary carbons of brominated cis-1,4-isoprene units, when 2D-NMR measurements were applied to the structural analysis of the brominated natural rubber. It was found that cis-trans isomerization of isoprene units took place during the bromination of DPNR with NBS.