Comparative study the hydrolytic degradation behavior of high-performance biobased aromatic-aliphatic liquid crystal copolyesters in different degradation medium

In this study, the hydrolytic degradation behavior of high-performance bio-based aromatic-aliphatic liquid crystal copolyesters (BTLCP)—synthesized from 4-hydroxybenzoic acid (HBA), phloretic acid (HPPA), vanillic acid (VA), and lactic acid (LA)—in proteinase K, phosphate buffer, and dilute alkaline solutions has been systematically and comparatively investigated. The degradation behavior was found to be correlated with the copolyester’s rigid and flexible molecular chain structure and composition. The weight loss after degradation was positively correlated with the LA content, as the aliphatic ester groups and amorphous regions of the molecular chain were most susceptible to chemical attack. The molecular chain further ruptured as degradation proceeded, causing the molecular weight to decrease sharply before leveling off after the seventh degradation period. Concurrently, the morphology of the copolyester flakes became coarser and more porous with increasing degradation time, suggesting a combined surface and bulk corrosion mechanism. Although the degraded copolyesters retained their liquid crystal behavior, the isotropic transition was observed below 350 °C, indicating a decrease in molecular chain rigidity. Moreover, the hydrophilicity of the copolyesters increased dramatically after degradation, especially for those containing more LA units, due to the generation of -OH and -COOH end groups from molecular chain scission. In summary, the results reveal that the hydrolytic degradation rate can be regulated by adjusting the composition and degradation medium. The synthesized BTLCPs containing more LA units exhibit excellent degradation performance and hydrophilicity, highlighting their potential for applications in biomedical and packaging fields.