The role of hydrogen bonding on a hydroxylated liquid crystal, bis [4-(5-hydroxypentyloxycarbonyl)phenylene] terephthalate

Hydroxyl-terminated liquid crystalline bis4-(5-hydroxypentyloxycarbonyl)phenylene] terephthalate (BHT) was prepared and compared with its non-hydroxylated analog, bis4-(pentyloxycarbonyl)phenylene] terephthalate (BPT). BHT, with the possibility to form intermolecular hydrogen bonding (H-bonding), has higher thermal transition temperatures (T_m and T_i) than BPT. Infrared spectroscopy was applied to prove the existence of H-bonding for BHT. An X-ray diffraction study suggests that the smectic A (S_A) phase is the only phase existing for BPT but for BHT, an interdigitated layered structure was found to be mixed with the S_A phase. The formation of this interdigitated layered structure is mainly due to the intermolecular H-bonding between the terminal hydroxyl and the external ester groups in BHT.