Synthesis and characterization of a thermotropic liquid crystalline hyperbranched polyester

BACKGROUND: Hyperbranched polymers have received increasing attention in the fields of medicine, homogeneous catalysis and materials science. Hydroxyl-functional aliphatic polyesters are one of the most widely investigated families of hyperbranched polymers. The research reported here is based on the preparation of a novel hyperbranched polyester and the modification of its terminal hydroxyl groups by biphenyl mesogenic units. RESULTS: 2,2,6,6-Tetramethylolcyclohexanol as a core and 8-[4'-propoxy(1,1-biphenyl)yloxy]octanoic acid as a mesogenic unit were synthesized. A hyperbranched polyester (HPE) was synthesized in one step and subsequently substituted by reaction of its terminal hydroxyl groups with the biphenyl mesogenic units to yield a novel liquid crystalline hyperbranched polyester (HPE-LC). The chemical structures of all compounds were confirmed using Fourier transform infrared, H-1 NMR and C-13 NMR spectroscopy. The thermal behavior and the mesogenic properties of the biphenyl mesogenic unit and HPE-LC were investigated using differential scanning calorimetry, polarized optical microscopy and wide-angle X-ray diffraction. The results demonstrated that the degree of branching of the HPE is ca 0.63. Both HPE-LC and the biphenyl mesogenic unit exhibit mesomorphic properties, but HPE-LC has a lower isotropic transition temperature and a wider transition temperature range than the biphenyl mesogenic unit. CONCLUSION: A novel liquid crystalline hyperbranched polyester was successfully synthesized, which exhibits mesomorphic properties. This polymer has good solubility in highly polar solvents and good thermal stability. (c) 2009 Society of Chemical Industry