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).