Synthesis and structure-property relationship of thermotropic liquid crystalline polyesters containing thiophene-aromatic and cycloaliphatic moieties

ABSTRACT

We report the structure and property characterization of a series of thermotropic liquid crystalline polyesters (TLCPs) composed of three different repeating units based on 1,4-hydroxybenzoic acid (HBA), 6-hydroxy-2-naphthoic acid (HNA), and 2,5-thiophenedicarboxylic acid/1,4-cyclohexanedimethanol (TDCA/CHDM), which are synthesized through two-step melt polymerization. The effect of the TDCA/CHDM-based repeating unit (0.0–10.0 mol%) on the structure, thermal and mechanical properties of the TLCPs with 75.0 mol% HBA and 25.0–15.0 mol% HNA were investigated. The polarized optical and electron microscopic images confirmed the presence of thermotropic liquid crystalline and fibrillar structures for all synthesized TLCPs. The glass transition and melting temperatures as well as the crystallinity index of the TLCPs were found to increase with increment of the TDCA/CHDM unit up to 5.0 mol% due to the improved interchain packing, but they decreased at higher amounts of 7.5–10.0 mol% TDCA/CHDM units owing to the enhanced flexibility by the cyclohexylene ring and the mismatching in the length between HNA and TCDA/CHDM units. In addition, there was a crystal lattice transition of TLCPs from pseudo-hexagonal to orthorhombic phases. Although the thermal decomposition temperature and elastic storage moduli of the TLCPs decreased with the amount of the TDCA/CHDM unit, all TLCPs remained stable up to 300°C and had excellent elastic moduli above 4.1 GPa at 50°C.

Graphical Abstract

KEYWORDS:

• Thermotropic liquid crystalline polyester
• cycloaliphatic unit
• thiophene-aromatic unit
• thermal property
• mechanical property

Acknowledgments

This work was supported by the Industrial Strategic Technology Development Program (Grant No. 20007862, 20009446, 20010999) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea).

Disclosure statement

All authors declare that there are no relevant financial or non-financial competing interests to report.

Additional information

Funding

This work was supported by the Ministry of Trade, Industry & Energy (MOTIE, Korea)[20007862, 20009446, 20010999].

Notes on contributors

Eun-Ji Choi

Eun-Ji Choi received her bachelor’s degree from the Department of Organic Materials Engineering, Chungnam National University in 2021, and is currently in the master's course in Applied Organic Materials Engineering. Her research focuses on the synthesis-structure-process-property relationship of novel thermotropic liquid crystalline polymers for high-performance fibers and super engineering plastics applications.

So-Jeong Lee

So-Jeong Lee obtained a bachelor’s degree in Materials Design Engineering from Kumoh National Institute of Technology in 2020 and is currently pursuing a master's degree in Applied Organic Materials Engineering at Chungnam National University. Her research mainly concentrates on the synthesis, processing, property analysis, and applications of wholly aromatic polyamides and polyesters derived from sustainable resources.

Young Gyu Jeong

Young Gyu Jeong received his doctoral degree in Materials Science and Engineering from Seoul National University in 2003 and spent three years as a postdoctoral research fellow at the University of Massachusetts Amherst. During 2006-2012 he served as assistant/associate professor of the Department of Materials Design Engineering at Kumoh National Institute of Technology. He is currently a professor at Chungnam National University. His research focuses on the design, synthesis, and characterization of polymeric materials and nanocomposites with high performance, multifunctionality, sustainability, and advanced applicaitons.