Facilely Synthesizing Ethynyl Terminated All-Aromatic Liquid Crystalline Poly(esterimide)s with Good Processability and Thermal Resistance under Medium-Low Temperature via Direct Esterification

Developing a facile strategy to synthesize thermosetting all-aromatic liquid crystalline poly(esterimide)s (LCPEIs) at medium-low temperature and endowing LCPEIs with good processability and high thermal resistance are still two big challenges. Herein, a new solution polymerization based on direct esterification under 120 °C is developed, overcoming bottlenecks of traditional melt and solution polymerizations. Besides, two new reactive LCPEIs (LCPEI-1 and LCPEI-2) terminated with 3-ethynylaniline (3-EA) were synthesized, and their structures and properties were compared with two control samples without 3-EA end groups. LCPEI-1 and LCPEI-2 not only show good processing characteristics including low melting temperature (Tm = 200 °C), low melting viscosity, and good solubility in solvent, but their cured samples also have high glass transition temperature (Tg = 192 and 225 °C) and high storage modulus, whereas control samples, even treated with similar thermal history as curing procedure for LCPEI-1 and LCPEI-2, have poor performances. Cured-LCPEI-2 exhibits the highest Tg among polyesters with low Tm values (<250 °C) reported. The mechanism behind outstanding performances of LCPEIs is discussed.