Effects of ionic liquids as catalysts on liquid crystal aromatic polyester based on thin-film polymerization technique

Liquid crystal aromatic polyesters (LCAPs) have been used in wide applications, such as chip packaging and airship skin. The traditional polymerization of LCAP is catalyzed by inorganic salts, for example, sodium acetate. Herein, we reported three kinds of ionic liquids (ILs) as catalysts to promote LCAP polymerization for the first time. The effects of ILs on the polymerization behaviors are investigated by in situ observing the liquid crystal (LC) phase behaviors based on the thin-film polymerization technique. The evolution of LC phase over time was detailly investigated by analyzing the emergence, fusion, and growth of LC phase. The temperature from 170 to 210 degrees C and the catalyst concentration in range from 0 to 0.5 wt% are compared, showing that temperature at 210 degrees C and catalyst concentration at 0.5 wt% are the best polymerization conditions for all ILs catalysts. In comparison with trimethylsulfonium iodide and piperidine acetate, 1-ethyl-3-methylimidazolium acetate has the best catalytic effect for the polymerization of LCAP in all experimental conditions. The successful polymerization was confirmed by FT-IR spectra, showing the increased intensity of vibration peak at 1735 cm-1 attributed to the generation of ester groups while the decreased intensities of vibration peaks at 1759 and 1370 cm-1. Catalytic activities of ionic liquids for LCAP polymerization.image