Theoretical studies on hydrogen-bonding interactions in hard segments of shape memory polyurethane-III: Isophorone diisocyanate

In this study, the hydrogen-bonding interactions in one widely used aliphatic hard segment (HS) of shape memory polyurethane, isophorone diisocyanate (IPDI), were investigated theoretically by density functional theory (DFT). The B3LYP/6-31G*method was used to calculate the equilibrium structures, Mulliken charges, hydrogen-bonding energies, and infrared (IR) spectra, in good agreement with experimental data. Due to chair-structure of cyclohexane ring, a great variety of hydrogen bonds can be formed in IPDI-based HSs. Bond distances R(N-H⋯O), which are in the range of 2.894-3.043 Å for CO hydrogen bonds, and 3.124 Å for ester O hydrogen bond, are in reasonable agreement with experimental values. The charge transfer on atoms N, H and O involved in hydrogen bonding occurs with the forming of hydrogen bond. The CO hydrogen bonding is much stronger than the ester O one. Two hydrogen bonds with one shared carbonyl group are not as strong as two normal hydrogen bonds with two private carbonyl groups. The number of the new absorption peaks in IR spectra is in accordance with the type of hydrogen bonds, which can be well forecasted by the DFT methods with more specific details. Compared with the MDI-based HS, the IPDI-based HSs can form much stronger hydrogen bonds. This study can supply in-depth understanding of the hydrogen-bonding mechanism in the HSs of IPDI-based polyurethane.