The recent developments of thermotropic liquid crystalline polymers

Chung, Tai‐Shung

doi:10.1002/pen.760261302

Cited by 203 publications

(96 citation statements)

References 125 publications

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“…Especially in their molten state, the liquid crystalline polymers demonstrate characteristic features such as marked shear rate dependency and low viscosity compared to those of such conventional polymers. In addition, a liquid crystalline polymer is characterized by its main chain so rigid as to allow it to be molten with little bending of its molecular chains, which can be highly oriented when it is subjected to slight shearing, making it crystalline while in a liquid state [12]. These characteristic properties of liquid crystalline polymers allow them to be categorized as one of highly functional materials for use in mechanical and electronic component parts, as well as in other special coating fields where they are molten and molded for use.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear Viscoelasticity of Fiber-Filled Liquid Crystaline Polymer Melts

Araki

Kitano

Maekawa

2002

Journal of Textile Engineering

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Section: Introductionmentioning

confidence: 99%

Nonlinear Viscoelasticity of Fiber-Filled Liquid Crystaline Polymer Melts

Araki

Kitano

Maekawa

2002

Journal of Textile Engineering

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“…POB has the similar problem derived from its intractability, and hence many thermotropic polyesters composed of p-oxybenzoyl unit as well as other aromatic copolyesters have been developed thus far. [3][4][5][6][7][8][9] Thermotropic polyesters composed of p-oxybenzoyl unit are modified to reduce the chain rigidity by copolymerization, and therefore sacrifices the eventual properties predicted from the chain structure of POB. We have succeeded in obtaining whiskers of POB and other aromatic polyesters using crystallization of oligomers during solution polymerization.…”

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confidence: 99%

Preparation of Poly(p-oxybenzoyl) Whisker in Paraffin Wax

Sarker

Kimura

Yamashita

2002

Polym J

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ABSTRACT:An influence of solvent on morphology as well as growth mechanism of poly(p-oxybenzoyl) whisker in paraffin wax (PW) was studied comparing with those in liquid paraffin (LPF). Furthermore, the condition for consecutive addition of oligomer was also examined to lengthen the whiskers in PW. Polymerizations of p-acetoxybenzoic acid were carried out in PW and LPF at 330• C. Larger number of whiskers having smaller length and width were formed in PW compared with that in LPF. PW was a poorer solvent than LPF and this lower miscibility leaded to the crystallization of lower DP n oligomers. Additionally, formation rate of oligomer was bigger in PW than LPF. These facts resulted in the higher degree of super saturation of oligomers which generated a larger number of nuclei having smaller size. Since the length was determined by the number of nuclei and the yield, the length eventually became shorter. On the basis of the formation mechanism of the whisker in PW, oligomers were added into polymerization system to lengthen the whisker. When oligomers were added to compensate the consumed oligomers while the tip angle was constantly kept at 80• C, the steady growth period was expanded and the length increased from 13.4 µm to 22.1µm. KEY WORDS Poly(p-oxybenzoyl) / Whisker / Paraffin Wax / Crystallization / Oligomer / Miscibility / Aromatic polyesters are characterized by the unique combination of thermal and mechanical properties and by a remarkable chemical resistance, which makes them useful high performance materials for various industrial applications such as reinforcement of composites, substitutions for asbestos and so on. However, wholly aromatic polyesters consisted of rigid-rod molecules show usually neither solubility or metlability under their decomposition temperatures. This intractability brings them about severe problems in industrial usage. Many attempts have been conducted with the aim of improving the poor processability from the point of both chemical modifications 1 and processing techniques. 2 Poly(p-oxybenzoyl) (POB) is a wholly aromatic polyester consisted of rigid-rod molecule and it is a hopeful candidate as high performance materials. POB has the similar problem derived from its intractability, and hence many thermotropic polyesters composed of p-oxybenzoyl unit as well as other aromatic copolyesters have been developed thus far. 3-9 Thermotropic polyesters composed of p-oxybenzoyl unit are modified to reduce the chain rigidity by copolymerization, and therefore sacrifices the eventual properties predicted from the chain structure of POB. We have succeeded in obtaining whiskers of POB and other aromatic polyesters using crystallization of oligomers during solution polymerization. [10][11][12][13][14][15][16][17][18][19] POB whiskers are prepared from p-acetoxybenzoic acid (p-ABA) in poor solvent such as liquid paraffin (LPF) with the elimination of acetic acid at high temperature solution polymerization, of which the average length is ca. 40 µm and the average width is 1.5 µm. These whiske...

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“…1,10,[23][24][25][26][27][28] The investigated systems mainly included Vectra TM A900e/polypropylen, 23, 24 LCP/poly(ether ether ketone)/poly(ether imide), 25 LCP/polycarbonate and 575…”

Section: Introductionmentioning

confidence: 99%

Morphology Control and Mechanical Properties of Liquid Crystalline Polymer-Polyamide Composite Fibers

Wang

Tao

Newton

et al. 2002

Polym J

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ABSTRACT:In this paper, we investigate the relationships between the viscosity ratio, morphology, and processing temperature of composite fibers comprising liquid crystalline polymer (LCP) and polyamide-66 (PA 66). Furthermore, we examine in details the effect of the LCP concentration on the phase microstructure and the mechanical properties of the composite fibers. The results show that, first, the optimal processing temperature of melt spinning of the composite fibers depends strongly on the viscosity ratio of LCP to PA 66 though the processing temperature range can be determined by the degradation temperature of PA 66 and the melting point of LCP. Secondly, the LCP phase structure/morphology in composite fibers can be controlled by the viscosity ratio of LCP to PA 66. Thirdly, the LCP phase structure/morphology are changed with LCP concentration for a fixed viscosity ratio/processing temperature. With an increase in LCP concentration, the morphology of LCP phase is changed from a fine fibril dispersed phase to a perfectly aligned continuous fiber reinforced phase in a rich LCP composite fiber. Finally, the mechanical properties of LCP composite fibers depend on the LCP phase structure/morphology and LCP concentration. The tensile properties of the composite fibers exhibit the positive synergy in the rich LCP composite fibers.KEY WORDS Composite Fibers / Morphology Control / Viscosity Ratio / Processing Temperature / Liquid Crystalline Polymer (LCP) Concentration / Mechanical Properties / The morphology of the materials, especially the morphology/microstructure of the LCP phase, has a strong influence on the mechanical properties of the composite materials comprising thermotropic liquid crystalline polymers (LCPs) and thermoplastic matrix. In general, the thermotropic LCPs do not directly transform to an isotropic melt when heated above their melting point, but to a state where the orientational long-range order is preserved whereas the long-range positional order breaks down. Thermotropic LCPs are essentially rigid-rod long-chain molecules with some irregularity or flexibility incorporated into the polymer chain to lower the melting point below the decomposition temperature. The rigid-rod molecular structure allows these materials to exhibit molecular order in a liquid mesophase. The highly oriented nature of LCPs produces highly anisotropic physical property and makes thermotropic LCPs quite attractive as a potential dispersed phase in in-situ reinforcing materials. The processing conditions affect the morphology and properties of the composites significantly. The processing conditions are also related to rheological properties of polymers, which determine the deformation and flow behavior of polymer materials in liquid, melt or solid form. In many industrial processes, polymer melts are subject to complex flows and temperature histories. To understand these complex flows, the response of the polymer melts in simple flow fields has been studied to determine material properties such as the viscosity, normal ...

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The recent developments of thermotropic liquid crystalline polymers

Cited by 203 publications

References 125 publications

Nonlinear Viscoelasticity of Fiber-Filled Liquid Crystaline Polymer Melts

Nonlinear Viscoelasticity of Fiber-Filled Liquid Crystaline Polymer Melts

Preparation of Poly(p-oxybenzoyl) Whisker in Paraffin Wax

Morphology Control and Mechanical Properties of Liquid Crystalline Polymer-Polyamide Composite Fibers

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