All-aromatic liquid crystal thermosets: New high-performance materials for structural applications 

Over the past two decades, there has been an increasing interest in all-aromatic crosslinked liquid crystal (LC) systems for structural, electronics and coatings applications. In this paper we will give a brief overview of our work on oligomeric liquid crystals end-capped with phenylethynyl reactive end-groups. All reactive oligomers were synthesized using standard melt-condensation techniques and the final products form homogeneous nematic melts over a wide temperature range (220-400 °C). The reactive LC oligomers could be cured at elevated temperatures (310-400 °C) to form true rigid-rod nematic networks. As will be demonstrated, this oligomer approach allows us to design all-aromatic nematic networks with a variety of favorable physical, mechanical and processing characteristics. Depending on the backbone chemistry, and end-group concentration, we can access liquid crystal thermosets with Tg's between 110-280 °C and storage moduli (E') of 2-5 GPa. The oligomeric nature of our reactive LCs results in excellent melt processing characteristics (|η*| ≥ 1 Pa.s at 100 rad.s^-1) and allows for the processing of complex structures such as fiber-reinforced composites. Based on our current results we are convinced that reactive all-aromatic liquid crystals can be interesting alternatives over existing high-performance polymers such as polyarylether ketones (PEEK and PEKK) polyphenylenesulfide (PPS) and polyetherimides (PEIs).