Hydrogen-Bond Interactions between Urethane−Urethane and Urethane−Ester Linkages in a Liquid Crystalline Poly(ester−urethane)

Abstract

Five model compounds (Uu, Us, DPT, DMT, and MB) and two liquid crystalline poly(ester−urethane)s with inherent urethane and internal and external ester groups were prepared to monitor the hydrogen-bond (H-bond) interactions of urethane−urethane and urethane−ester (including internal and external esters). The model compounds were used to evaluate the extinction coefficient ratios between different free and bonded carbonyl absorption modes in the infrared spectra. The results show extinction coefficient ratios of efree,u:efree,ext:ebonded,ext:ebonded,u:efree,int = 0.84:0.81:0.87:1.23:1.0. These ratios can then be used to approach mole fractions of different carbonyl groups in the oligomeric and polymeric poly(ester−urethane)s (as PEU-L and PEU-H, respectively) at different temperatures. For both PEU-L and PEU-H, their external ester carbonyl groups can compete efficiently with urethane carbonyl groups for H-bonds at elevated temperatures. Oligomeric PEU-L exhibited a major increase on the external ester car...