The FT-IR spectra of the solid films prepared from waterborne
PUs were similar to each other and therefore only the spectrum of
PU-21 is shown in Fig. 1. The isocyanate (–N C O) absorption peak
at 2270 cm−1 disappeared, indicating that the –N C O groups of
IPDI at each terminus of the PU prepolymers reacted completely.
A broad absorption at 3315 cm−1 is due to the N–H stretching of
urethane bonds (NH–COO). The carbonyl absorption band is split
into two peaks: one at 1700 cm−1 caused by urethane carbonyls
and another one at 1650 cm−1 caused by urea carbonyls [18].