A structural study of epoxidized natural rubber (ENR-50) and its cyclic
dithiocarbonate derivative was carried out using NMR spectroscopy techniques. The
overlapping 1H-NMR signals of ENR-50 at δ 1.56, 1.68–1.70, 2.06, 2.15–2.17 ppm were
successfully assigned. In this work, the 13C-NMR chemical shift assignments of ENR-50
were consistent to the previously reported work. A cyclic dithiocarbonate derivative of
ENR-50 was synthesized from the reaction of purified ENR-50 with carbon disulfide
(CS2), in the presence of 4-dimethylaminopyridine (DMAP) as catalyst at reflux
temperature. The cyclic dithiocarbonate formation involved the epoxide ring opening of the
ENR-50. This was followed by insertion of the C–S moiety of CS2 at the oxygen attached
to the quaternary carbon and methine carbon of epoxidized isoprene unit, respectively. The
bands due to the C=S and C–O were clearly observed in the FTIR spectrum while the
1H-NMR spectrum of the derivative revealed the peak attributed to the methylene protons
had split. The 13C-NMR spectrum of the derivative further indicates two new carbon peaks
arising from the >C=S and quaternary carbon of cyclic dithiocarbonate. All other 1H- and
13C-NMR chemical shifts of the derivative remain unchanged with respect to the ENR-50.