Precise compositional analysis of liquid crystalline aromatic polyesters containing aromatic amide linkages by thermally assisted hydrolysis and methylation-gas chromatography

Multi-component liquid crystalline aromatic polyesters (LCPs) containing 4-aminophenol (PAP) units to form amide linkages were characterized by thermally assisted hydrolysis and methylation-gas chromatography (THM-GC). Under the given THM conditions (300 °C; in the presence of 25 wt% tetramethylammonium hydroxide in methanol), the aromatic amide linkages in the LCP chains were only methylated but hardly cleaved, whereas the ester bonds almost quantitatively decomposed into methyl esters and methyl ethers. Thus dimeric and trimeric products consisting of PAP and another monomer unit linked through methylated amide linkage(s) were observed in the THM chromatograms along with dimethyl derivatives of the monomer units other than PAP. The compositions of the LCP samples containing PAP units were then determined from the relative peak intensities observed in the THM chromatograms, and showed quite good agreement with the original monomer compositions in feed with superior reproducibility; less than 1% relative standard deviation.