All‐aromatic liquid crystal thermosets: New high‐performance materials for structural applications

Dingemans, Theo J.; Knijnenberg, A.; Iqbal, Mazhar; Weiser, Erik S.; Stclair, T. L.

doi:10.1080/14645180701470371

Cited by 11 publications

(4 citation statements)

References 28 publications

(30 reference statements)

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“…Although interest in TLCPs and their composites has been increasing, to achieve enhanced physical properties, most studies have focused on rigid rod-type TLCPs with completely aromatic monomers in the main chain [8,9]. In almost all TLCPs, the thermo-mechanical properties have been enhanced by using straight, rigid rod-shaped monomer units, including terephthalic acid (TPA), hydroquinone (HQ), 4,4 -biphenol (BP), p-hydroxybenzoic acid (HBA), 6-hydroxy-2-naphthoic acid (HNA), naphthalenediol…”

Section: Introductionmentioning

confidence: 99%

Dependence of the Physical Properties and Molecular Dynamics of Thermotropic Liquid Crystalline Copolyesters on p-Hydroxybenzoic Acid Content

et al. 2020

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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.

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Section: Introductionmentioning

confidence: 99%

Dependence of the Physical Properties and Molecular Dynamics of Thermotropic Liquid Crystalline Copolyesters on p-Hydroxybenzoic Acid Content

et al. 2020

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“…Some commonly used monomers include terephthalic acid, hydroquinone, 4,4′-biphenol, and p -hydroxybenzoic acid (HBA), which impart good physical and thermo-mechanical properties in the TLCPs. Alternatively, TLCPs composed of monomers such as 6-hydroxynaphthoic acid (HNA), naphthalene diol derivatives, and naphthalene dicarboxylic acid isomers, in which the basic structure of the main chain contains a para-substituted carboxyl group or a benzene ring, exhibit high meting temperatures of approximately 600 °C 6 – 8 .…”

Section: Introductionmentioning

confidence: 99%

Annealing effect of thermotropic liquid crystalline copolyester fibers on thermo-mechanical properties and morphology

Park

Kim

et al. 2022

Sci Rep

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A series of thermotropic liquid crystal copolyesters (Co-TLCPs) was prepared by melt polymerization using 2,5-diethoxyterephthalic acid (DTA), 2,7-dihydroxynaphthalene (DHN), and p-hydroxybenzoic acid (HBA) monomers, where the HBA content was varied (0–5 mol). At 3 mol HBA, the Co-TLCPs formed nematic mesophases, while below this concentration, the liquid crystalline phase did not appear. The Co-TLCP sample with 3 mol HBA was subjected to melt spinning and heat-treated under various conditions (temperature and time) to investigate their effect on the thermo–mechanical properties and degree of crystallinity. The objective was to determine the critical heat treatment condition that can maximize the properties of the spun Co-TLCP fibers. The microstructure of the heat-treated fiber was investigated using scanning electron microscopy, and the optimal annealing conditions were confirmed based on the morphology of the fiber, which exhibited a skin–core structure owing to the varying heat and pressure conditions applied during spinning.

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“…Recently, we reported our results on a reactive TLCP concept, where we modified a well‐known TLCP based on 4‐hydroxybenzoic acid (HBA) and 6‐hydroxy‐2‐naphthoic acid (HNA) (Vectra™), with reactive phenylethynyl end groups 11, 12. By reducing the molecular weight of the polymer backbone, the melt viscosity could be reduced from 10,000 Pa s −1 , which is typical for high‐molecular weight Vectra, to 100 Pa s −1 for a 5000 g mol −1 analog, and at the same time T m could be reduced by as much as 100 °C for the 1000 g mol −1 analog.…”

Section: Introductionmentioning

confidence: 99%

All‐aromatic liquid crystalline thermosets with high glass transition temperatures

Iqbal

Norder

Mendes

et al. 2009

J. Polym. Sci. A Polym. Chem.

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We have synthesized and characterized a new family of low melting allaromatic ester-based liquid crystal oligomers end-capped with reactive phenylethynyl end groups. In a consecutive, high-temperature step, the reactive end groups were thermally activated and polymerization was initiated. This reactive oligomer approach allows us to synthesize liquid crystal thermosets with outstanding mechanical and thermal properties, which are superior to well-known high-performance polymers such as PPS and PEEK. We have modified an intractable LC formulation based on hydroquinone and terephthalic acid, with M n ¼ 1000, 5000, and 9000 g mol À1 , and varied the backbone composition using isophthalic acid, resorcinol, 4hydroxy-benzoic acid, 6-hydroxy-2-naphthoic acid, and chlorohydroquinone. All fully cured polymers showed glass transition temperatures in the range of 164-275 C, and high storage moduli at room temperature ($ 5 GPa) and elevated temperature ($ 2 GPa at 200 C). All oligomers display nematic mesophases and in most cases, the nematic order is maintained after cure. Rheology experiments showed that the phenylethynyl end group undergoes predominantly chain extension below 340 C and crosslinking above this temperature. Highly aligned fibers could be spun from the nematic melt, and we found that the order parameter hP 2 i was not affected by the chain extension and crosslink chemistry.Scheme 2. Synthesis of the terephthalic acid (TA)-and hydroquinone (HQ)-based liquid crystalline oligomers with phenylethynyl end groups. The oligomers in series 1 are terminated with the more linear para-substituted reactive end groups, whereas the series 2 are end capped with the meta-substituted phenylethynyl functionalities. ALL-AROMATIC LIQUID CRYSTALLINE THERMOSETS

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All‐aromatic liquid crystal thermosets: New high‐performance materials for structural applications

Cited by 11 publications

References 28 publications

Dependence of the Physical Properties and Molecular Dynamics of Thermotropic Liquid Crystalline Copolyesters on p-Hydroxybenzoic Acid Content

Dependence of the Physical Properties and Molecular Dynamics of Thermotropic Liquid Crystalline Copolyesters on p-Hydroxybenzoic Acid Content

Annealing effect of thermotropic liquid crystalline copolyester fibers on thermo-mechanical properties and morphology

All‐aromatic liquid crystalline thermosets with high glass transition temperatures

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