The absorption peak at 1730 cm−1 occurred only in the spectra of the films made from the latex mixture (spectra c−e,
Figure 4). This band is presumably associated with the CO functionality and possibly with the ester (R−COO−R′)
functional groups in the coagent and the ketone (R−CO−R′) groups in the photoinitiator.7 Thus, this peak was not seen
in the spectra of the films made of pure NR latex and the 2 h irradiated pure NR latex (spectra a and b, Figure 4), as they did
not contain any photoinitiator and coagent molecules.