Liquid Crystalline Polymers and Their Nanocomposites

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Processing and Engineering".

Deadline for manuscript submissions: closed (31 May 2020) | Viewed by 3350

Special Issue Editor


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Guest Editor
Department of Polymer Science and Engineering, Kumoh National Institute of Technology, Gumi 730‐701, Korea
Interests: synthesis of liquid crystalline polymers; liquid crystalline polymer blends with engineering plastics; nanocomposites using clay; CNTs and graphene; colorless transparent polyimide; super gas barrier film
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The liquid crystal (LC) states of polymers were discovered with the discovery of aramids, such as poly(p-phenylene terephthalamide) (Kevlar) and poly(p-benzamide), by DuPont de Nemours Co. in the 1970s. These aromatic polyamides form LC states when dissolved in a solvent (lyotropic), such as sulfuric acid. In addition, the commercialization of aromatic polyesters (e.g., Xydar® and Vectra®) that form LC states in melts (thermotropic) in the 1980s sparked the continued and unabated growth of the field of LC polymers (LCPs). Wholly aromatic LCPs are highly crystalline, insoluble, and very often interactive materials. These polymers have a very high melting temperature, and, thus, they cannot be readily processed by spinning or molding. However, LCPs should be structurally modified to overcome these processing issues and prevent their thermal degradation before melting. The most common method for structural modification is to combine different mesogenic monomers, such as bulky side substituents, flexible alkyl side groups, or kink (nonlinear)-structured monomers.

Nanocomposites are one of the most important classes of synthetic engineering materials. The incorporation of organic/inorganic hybrids can yield materials that possess excellent stiffness, strength, and gas barrier properties with far less inorganic content than is used in conventionally filled polymer composites: the higher the degree of delamination in polymer/nanofiller composites, the greater the enhancement of these properties. Nanofillers can be categorized on the basis of their dimensions, such as one-dimensional fillers (nanotubes and nanowires), two-dimensional fillers (clays and graphene), and three-dimensional fillers (spherical and cubic nanoparticles).

This Special Issue, entitled “Liquid Crystalline Polymers and Their Nanocomposites”, will consider a broad range of LCPs, such as engineering materials for high-performance LCPs, high-temperature LCPs, and new synthetic LCPs. This Special Issue will also consider LCP blends with engineering polymers and organic–inorganic LCP nanocomposites.

Prof. Dr. Jin-Hae Chang
Guest Editor

Keywords

  • thermotropic liquid crystal polymers (LCPs);
  • lyotropic LCPs;
  • synthesis of new LCPs;
  • LCP blends/nanocomposites;
  • structure–property relationship in LCPs;
  • application of LCP;
  • processing of LCP;
  • molecular dynamics in LCP;
  • liquid crystalline thermoset polymer.

Published Papers (1 paper)

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18 pages, 4624 KiB  
Article
Dependence of the Physical Properties and Molecular Dynamics of Thermotropic Liquid Crystalline Copolyesters on p-Hydroxybenzoic Acid Content
by Gi Tae Park, Won Jun Lee, Jin-Hae Chang and Ae Ran Lim
Polymers 2020, 12(1), 198; https://doi.org/10.3390/polym12010198 - 12 Jan 2020
Cited by 10 | Viewed by 2972
Abstract
Two series of thermotropic liquid crystal copolymers (TLCPs) with different monomer structures and compositions were synthesized. The copolymers in the first series consisted of 2,5-diethoxyterephthalic acid (ETA), hydroquinone (HQ), and p-hydroxybenzoic acid (HBA), whereas those in the second series contained ETA, 2,7-dihydroxynaphthalene [...] Read more.
Two series of thermotropic liquid crystal copolymers (TLCPs) with different monomer structures and compositions were synthesized. The copolymers in the first series consisted of 2,5-diethoxyterephthalic acid (ETA), hydroquinone (HQ), and p-hydroxybenzoic acid (HBA), whereas those in the second series contained ETA, 2,7-dihydroxynaphthalene (DHN), and HBA. In both series, the molar ratio of HBA to the other monomers varied from 0 to 5. The thermal properties, degree of crystallinity, and stability of the liquid crystalline mesophase of the copolymers obtained at each HBA ratio were evaluated and compared. Overall, at each HBA content, the DHN-containing copolymer had better thermal properties, but the HQ-containing copolymer exhibited a higher degree of crystallinity and a more stable liquid crystalline mesophase. Furthermore, similar thermal stabilities were observed in both series. The dependence of the molecular dynamics of the TLCPs on the monomer structure was explained using 13C magic-angle spinning/cross-polarization nuclear magnetic resonance spectroscopy. An in-depth investigation of the relaxation time of each carbon revealed that the molecular motions of the TLCPs were greatly influenced by the structures of the monomers present in the main chain. The molecular dynamics of the HQ and DHN monomers in the two series were evaluated and compared. Full article
(This article belongs to the Special Issue Liquid Crystalline Polymers and Their Nanocomposites)
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