Solid-state and time domain NMR to elucidate degradation behavior of thermally aged poly (urea-urethane)

Abstract

We have demonstrated that solid-state and time-domain Nuclear Magnetic Resonance spectroscopy (NMR) techniques are effective in monitoring the degradation site of poly (urea-urethane). We prepared two types of commercial poly (urea-urethane), Urethane-A and Urethane-B, and aged them at 100 °C for up to 10000 h. We performed tensile strength tests and solid-state NMR experiments, in which 13C and 15N NMR spectra and T2 were collected. The tensile strength of Urethane-A decreased, increased and decreased again, whereas that of Urethane-B decreased at a lower rate with aging. Solid-state NMR experiments clearly showed that the degradation of Urethane-A was caused by molecular chain scission and cross-linking in its urea bonds, and that of Urethane-B occurred owing to molecular chain scission in its urethane bonds. T2 had three components, short T2 (T2S), intermediate T2 (T2I) and long T2 (T2L), whose fractions were xS, xI and xL, respectively. We have demonstrated that molecular chain scission in urea bonds decreases xS and increases xL, and that in urethane bonds increases T2I and T2L without changing all the T2 fractions.