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Major infrared bands of PUs.
| Wavenumber (cm−1) | Assignment |
|---|---|
| 3445 | N–H stretching (free) |
| 3320–3305 | N–H stretching (hydrogen bonded) |
| 2940 | Asymmetric C–H stretching |
| 2860 | Symmetric C–H stretching |
| 1730 | C=O stretching (free) |
| 1710–1705 | C=O stretching (hydrogen bonded—soft segment) |
| 1645–1635 | C=O stretching (hydrogen bonded—hard segment) |
