The polyurethanes are synthesized from the biphenyl-4,4′-diol (mesogenic biphenol) and 1,3-Bis(isocyanatomethyl) cyclohexane, using (CH 2) of 2, 6 and 11 units as flexible alkylene spacer, respectively. FTIR detects the hydrogen bond in the thermotropic liquid crystalline polyurethane. FTIR spectra show a new CO absorption with lower wavenumber at around 1658 cm-1 is assigned to "bifurcated" hydrogen bonded CO group - a CO with higher strength hydrogen bonds. The distributions of "bifurcated" hydrogen bonded CO are increased substantially along with increasing the flexible spacer length in polymer backbone. The "bifurcated" hydrogen bond existed not only at the temperature below Tg, but also existed at the temperature far higher than Tm and Ti. It almost is independent of temperature and exhibits a stable interaction (or strucuture) throughout a wide temperature range, differences from the normal liquid crystalline polyurethanes. It is worthy of predicting the thermotropic liquid crystalline polyurethane with "bifurcated" hydrogen bond would enhance its performances.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics