Design and In-Depth Characterization of Liquid Crystalline Polyesters for Lower Melting Points and Wider Processing Windows

This paper presents a thorough examination of thermotropic liquid crystalline polyesters (LCPs) designed to achieve lower melting points and wider nematic windows without sacrificing their strength or stability. The work begins by synthesizing fully aromatic LCPs and then systematically introducing aliphatic segments or partially crystalline polyesters—such as PET, PEN, PBT, PBN, and PHN—to modify melting temperatures (Tₘ) and phase-transition behavior. Comprehensive characterization was conducted using techniques such as differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarized light microscopy (PLM), wide-angle X-ray scattering (WAXS), and nuclear magnetic resonance (NMR). These results indicate that incorporating flexible or semicrystalline domains broadens the temperature range in which the polymers exhibit a nematic phase, thereby improving processability. In particular, formulations containing longer aliphatic diacids, such as octanedioic or decanedioic acid, showed lower Tₘ values and significantly expanded the temperature windows for nematic ordering. TGA measurements confirmed that an elevated fraction of aromatic units enhances thermal stability, whereas aliphatic constituents support easier processing. WAXS and fiber diffraction analyses revealed a higher degree of crystallinity in the LCPs enriched with PET, correlating with a stronger mechanical performance. Blending these modified LCPs with common thermoplastics (for instance, PET, PP, and ABS) resulted in improvements in tensile strength and overall mechanical behavior, suggesting that these materials are promising candidates for advanced composites. Moreover, detailed analyses of the reaction times and catalysts highlighted the delicate balance between achieving a sufficiently high molecular weight and maintaining tractable melt viscosities. Altogether, this study offers a roadmap for tuning LCP architectures to produce materials with optimized thermal, mechanical, and processing characteristics, thereby widening their suitability for applications ranging from high-performance fibers to industrial-scale thermoplastic composites.