Thermotropic Liquid Crystalline Polymers

Abstract

Herein we present recent studies on the nature of thermotropic liquid crystalline polymers (LCPs) and their progress. Side‐chain liquid crystals are also discussed briefly, showing the similarities and differences between these closely related molecules. We summarize and review the newly developed thin‐film polymerization technique for the investigation of liquid crystalline formation as a function of monomer moieties, and for the study of reaction kinetics, evolution of liquid crystal texture, and surface energy during polycondensation reactions. We also highlight various modification approaches to yield main‐chain LCPs suitable for conventional processing equipment, without compromising the unique liquid crystalline characteristics and superior mechanical properties. The thermal stability, degradation behavior, and crystallization kinetics of commercially available main‐chain LCPs are recapitulated. Attention is also given to the rheology, polymer blends, micro‐ and nanostructures, processing of LCPs, and their applications. In the past decade, investigations of thermotropic LCPs have decreased from the high interest and publication rate of the latter part of the twentieth century. However, the number of monomer combinations giving rise to main‐chain thermotropic polymers has increased and the origin of LCP rheology and morphology have been elucidated. The most important new work is the invention and description of thermotropic thermosets.

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

“…Liquid crystal polyesters (LCPs) have been widely employed in electronics, vehicles and aerospace, because of the high thermal resistance, excellent mechanical strength, low moisture absorption and good dielectric properties. [1][2][3] In the last decades, liquid crystal aromatic polyester (LCAP) fibers have attained continuous attention in the fields of specialty cordage, airship skin and cable reinforcement materials, and so forth, 2,4 because Zexi Wu and Caijie Shi contributed equally to this study.…”

“…Commonly, inorganic salts, such as sodium acetate and zinc acetate, which are used as catalysts to promote the polymerization rates. 3 The kinetics of the polymerization show that the catalyst, temperature and concentration play vital roles in the final product. 5 However, the residual metal could damage the final quality of the product and cause the potential threats to human health.…”

“…18,19 Subsequently, it has been widely employed to investigate the polymerization kinetics of liquid crystal polymers, due to the device convenience, visualization of polymerization and timeliness of data collection. 20,21 Given the excellent properties and extensive applications of commercial LCAP product of Vectran ® , 3,22 in this contribution, three kinds of ILs, including trimethylsulfonium iodide ([TMS][I]), piperidine acetate ([PDM][Ac]) and 1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]), were employed as catalysts to catalyze the polymerization of LCAP. Temperature and catalyst content were varied to investigate the optimal polymerization conditions, which were studied by in situ observing the evolution of LC phase over time based on thin-film polymerization technique.…”

“…Liquid crystal polyesters (LCPs) have been widely employed in electronics, vehicles and aerospace, because of the high thermal resistance, excellent mechanical strength, low moisture absorption and good dielectric properties 1–3 . In the last decades, liquid crystal aromatic polyester (LCAP) fibers have attained continuous attention in the fields of specialty cordage, airship skin and cable reinforcement materials, and so forth, 2,4 because the oriented crystal domains happening in spinning process result in greater physical properties, such as tensile strength and modulus and thermal‐resistance, meanwhile, the all‐aromatic structures endow LCAP good UV‐resistance, strong cut‐resistance and high flame retardance 2,4 .…”

“…LCAPs are synthesized by condensation polymerization via a transesterification reaction based on the acetylated and carboxylated monomers. Commonly, inorganic salts, such as sodium acetate and zinc acetate, which are used as catalysts to promote the polymerization rates 3 . The kinetics of the polymerization show that the catalyst, temperature and concentration play vital roles in the final product 5 .…”