The influence of bisphenol AF unit on thermal behavior of thermotropic liquid crystal copolyesters

• The thermotropic liquid crystal polyesters P-BPAFx containing BPAF unit were synthesized and characterized.
• P-BPAFx shows lower melting temperature and higher glass transition temperature when compared with parent polyester P-HBA70.
• The thermal stability of P-BPAFx was evaluated by Kissinger and Kissinger-Akahira-Sunose (KAS) methods.
• The P-BPAF 2.5 showed better thermal stability than that of P-HBA70, higher char yield is observed for all polyesters containing BPAF unit.

In this study, a series of thermotropic liquid crystal copolyesters P-BPAFx modified with 2.5–10 mol% of bisphenol AF (BPAF) and terephthalic acid (TA) were synthesized via melt polymerization. The structure and properties of P-BPAFx were characterized by various measurements. The melting temperature decreased from 260 to 220 °C and glass transition temperature increased from 70 to 118 °C after introduction of BPAF and TA units, showing P-BPAFx can easily be processed in a lower temperature and have a more broad application temperature. The thermal degradation behavior was evaluated by SEM, FTIR and thermogravimetric analysis (TG). The activation energy was obtained from Kissinger and Kissinger-Akahira-Sunose (KAS) methods, and was investigated comparatively with P-HBA70. It was found that the addition of 2.5 mol% BPAF units improve thermal stability, and much higher char yield was observed for those copolyesters containing BPAF unit.