Effect of a fluorine lateral moiety on the liquid crystallinity of wholly aromatic polyester-amides

We have identified the effect of a fluorine lateral moiety on the liquid crystallinity of wholly aromatic polyester-amides. The evolution of liquid crystal texture for two reaction systems, p-acetoxybenzoic acid (ABA)/acetoxy acetanilide (AAA)/3-fluorophthalic acid (FPA) and ABA/AAA/phthalic acid (PA), were examined and compared by in situ polymerizations under a polarizing microscope with a heating-stage. The fluorine lateral moiety was found to have an adverse effect on the liquid crystallinity. The system containing FPA needs higher critical ABA content (the rigid and straight monomer) to form liquid crystallinity than the system containing PA. In addition, the LC phase emerges faster in the ABA/AAA/PA system than in the ABA/AAA/FPA system during polymerizations. Amorphous phase reappears in the later stage of thin film polymerizations for both systems if ABA content is in a particular range. However, the ABA/AAA/FPA system has a greater amorphous area than the ABA/AAA/PA system.