The effects of hydrogen bonding on the liquid crystalline behavior of semiflexible poly(urethaneester)s

Abstract The peculiar liquid crystalline behavior of two poly(urethane‐ester)s TDI‐C6C4 and TDI‐C6C8 is reported. Evidence is provided of the formation of two nematic mesophases, a cybotactic nematic and a conventional nematic mesophase, in TDI‐C6C8 and of one cybotactic nematic mesophase in TDI‐C6C4. IR spectroscopy indicates that different hydrogen bonded and non‐bonded structures occur with varying temperature. The transition from the nematic cybotactic mesophase to the nematic mesophase, or to the isotropic phase, is accompanied by a substantial decrease of the strength of the hydrogen bonds. This is also reflected in the dynamic‐mechanical behavior of these poly(urethane‐ester)s which is similar to the one of slightly crosslinked thermoreversible networks.