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

• Published in: Macromolecules Vol. 32; no. 9; pp. 3068 - 3079
• Main Authors: Yen, Fu-Sen, Lin, Lieh-Li, Hong, Jin-Long
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 04.05.1999
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Structure, morphology and analysis; Esterurethane polymer; Liquid crystal polymers; Model compound; Thermotropic state; Temperature effect; Smectic state; Mesomorphic state structure; Experimental study; Hydrogen bond
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma9804186

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 εfree,u:εfree,ext:εbonded,ext:εbonded,u:εfree,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 carbonyl groups once heated to the mesomorphic state; in contrast, carbonyl variations on PEU-H proceeded in a continuous manner before the isotropization temperature. X-ray diffraction patterns suggest that PEUs form a smectic A layered structure. This result coupled with infrared study provided us the chain conformations of PEUs in their mesomorphic states.