Aromatic thermotropic

Cheng LP, Dwan AH, and Gryte CC. Wholly aromatic thermotropic liquid crystalline polyesters of 4,4 -biphenol, substituted biphenols, and l,l -binaphthyl-4,4 -diol with 3,4 -benzophenone dicarboxylic acid. J. Polym. Sci. Polym. Phys. B 1995 33 211-225. 

During the course of our study, we had the opportunity to evaluate the only available all aromatic, thermotropic polyester, LCP2000 from Celanese. Presumably it was a copolymer containing hydroxybenzoic (HBA) and hydroxy naphtholic acid (HNA) moieties. The sample was subjected to fiber spinnings and plastic moldings as were the thermotropic polyester-carbonates, using the same equipment and under comparable conditions. 

The unique molecular packing of rod-like chains in liquid crystalline polymers (LCP) closely resembles the extended chain structure of highly oriented flexible chain polymers, suggesting that these materials are good candidates for barrier applications. Thermotropic LCP s, first developed in the early 1970 s, have been the object of much interest because of their excellent mechanical properties and ease of product fabrication. Preliminary observations have shown that a commercially available wholly aromatic thermotropic copolyester has gas permeability coefficients that are lower than those of polyacrylonitrile (4.). These results raise some fundamental questions as to the nature of the mechanism for transport of small molecules through a matrix of ordered rigid rod-like chains. 

It is far beyond the scope of this chapter to present a comprehensive overview on the different structures of aromatic main chain LCPs and take into account the various property and application aspects. The objective of this chapter is to discuss the impact of structural concepts in modifying the properties of aromatic LCPs, focusing here on aromatic thermotropic LC polyesters. This will be discussed for selected examples. Conclusions from the work on polyesters are transferrable to other classes of thermotropic and lyotropic aromatic polymers. 

Gopakumar et al. [10] reported the in situ compatibilization of poly(phenylene sulfide) (PPS)/wholly aromatic thermotropic liquid crystalline polymer (TLCP) Vectra A950 blends by reactive extrusion. The authors prepared the in situ compatibilized PPS/TLCP blends in a twin-screw extruder by reactive blending of PPS and TLCP in the presence of dicarboxyl-terminated poly(phenylene sulfide) (DCTPPS). Block copolymer was formed during reactive blending, by transesterification reaction between carboxyl... 

Gopakumar, T. G., Ronrathnam, S., Lele, A., Rajan, C. R., and Fradet, A. 1999. In situ compatibilisation of poly(phenylene sulphide)/wholly aromatic thermotropic liquid crystalline polymer blends by reactive extrusion Morphology, thermal and mechanical properties. Polymer 357-364. 

Yerlikaya Zekeriya, Aksoy Serpil, Bayramli Erdal. (2001). Synthesis and Characterization of Fully Aromatic Thermotropic Liquid-Crystalline Copolyesters Containing m-hydroxybenzoic Acid Units J. Polym. Sci. A, 39(19), 3263-3277. 

Bi Shuguang, Zhang, Yi., Bu Haishan, Luise Robert, R., Bu Jenny, Z. (1999). Thermal Transition of a Wholly Aromatic Thermotropic Liquid Crystalline Copolyester. J. Polym. Sci. A, 37(20), 3763-3769. 

The conformational properties of polymer molecules with mesogenic groups in the main chain were studied in the series of alkylene-aromatic thermotropic polyesters in which the length of flexible methylene parts was varied polydeca-, penta- and tetramethylene-tere-phthaloyl-di-para oxybenzoate (P-IOMTB, P-5MTB, P-4MTB). 

Another aspect of morphology characterization is spectroscopic analyses of the molecular orientation. The simplest and most often used method is infrared (IR) spectroscopy. Although IR techniques cannot investigate the multilayered texture, they can readily provide vivid one- or two-dimensional profiles of molecular orientation vs. position. Bensaad et al. [17] used normal incidence specular reflection to characterize the orientation profile on the surface of an injection molded plaque (6 cm X 6 cm x 0.4 cm) made of a wholly aromatic thermotropic... 

Could a similar phenomenon occur in the melt Were thermotropic polymers possible They were possible, and indeed the number reported to date by academic and industrial researchers is nearly beyond count. In addition, as it later turned out, aromatic thermotropic polymers were found to offer a great many more useful properties than just their now well-known tensile capabilities. These polymers are injection moldable, albeit at temperatures in the vicinity of 400° C, a temperature not compatible with common melt-spinning equipment. The rate of thermal degradation of such a polyester at 400° C makes stable fiber production particularly difficult. Moreover, most conventional injection-molding equipment requires modification to operate at the high temperatures needed to ensure reasonable processing of this polymer. 

Compared with aromatic thermotropic polyesters, which never form a smectic layered structure, polyimides have very strong intermolecular interactions due to the imide group. This may be attributed to the high polarity of the imide group. 

Y.-K. Yun, J.-l. Jin, and M. Lee, Wholly aromatic thermotropic Uquid crystalline polyesters of 2-(a-phenylisopropyl) hydroquinone copolymers with 1,1 -Biphenyl-4,4 -diol and 2,6-dihydroxyn hthalene. Journal of Polymer Science Part A Polymer Chemistry, 35, 2777... 

M. H. B. Skovby, R. Lessel, and J. Kops, Thermal properties of some fuUy aromatic thermotropic liquid crystal polyesters. Journal of Polymer Science Part A Polymer Chemistry,... 

Aromatic thermotropic liquid crystal polyesters (Ar-TLCP s) and TLCP s containing aliphatic linkages can be compatibilized as binary-TLCP blends by transesterification. The morphology and physical properties of the resultant binary-TLCP blend are dependent on the blockiness, composition and viscosity ratios of the two TLCP components. Polycarbonate (PC) can also be blend compatibilized with either TLCP s or binary-TLCP blends, by transesterification of aliphatic linkages from the TLCP s into the PC. In this work, the degree of selective transesterification is quantified and its effect on TLCP blend compatibility is described... 

Aromatic thermotropic liquid-crystalline polyesters, compatibilization, 70-81 Average directional cosine of radial fiber direction, 41-42... 

The primary motivation for industrial participation in the development of liquid crystalline polymers was the search for high performance tensile properties, i.e., fiber tensile strength and modulus. As it later turned out, the wholly aromatic, thermotropic polyesters were found to offer a great many more useful properties than just their now well-known tensile capabilities. 

As a result of their anisotropic nature and consequent processability to near extended chain solid state structures, Kevlar (poly(p-phenylene terephthalamide) and the aromatic thermotropic polyesters approach their theoretical tensile moduli rather closely. Their fibers calculate to about 1500 g/d and can be formed experimentally in a range of 1000-1400 g/d. 

Structures Providing Tractability in Aromatic Thermotropic Polyesters... 

DuPont workers have described (7) a wide variety of tractabilizing molecules and the thermotropic polyesters derived therefrom. Their research has focused for the most part on ring substituted monomers such as chloro, methyl or phenyl substituted hydroquinone and swivel" or linked ring molecules, examples of which are 3,4 or 4,4 functionally (hydroxy or carboxy) disubstituted diphenyl ether, sulfide or ketone monomers. Use of the parallel offset or crankshaft" geometry provided by 2,6 functionally disubstituted naphthalene monomers has been the major thrust of the Celanese Corporation development of easily processed, high performance wholly aromatic thermotropic polyesters. 

A fifth factor is certainly ease of preparation and in this characteristic the melt prepared thermotropic polymers are particularly favored. All of the polymers described thus far may be made in a conventional melt acidolysis process starting with the acetoxy derivatives of the hydroxyl containing monomers used. A typical polymerization scheme is shown in Figure 8, the preparation of the two component polyester derived from the acetylated hydroxybenzoic and hydroxynaphthoic acids. The polymerization may be carried out with or without added catalysts. The poly(ester-amides) commented on here, and the more recently reported aromatic, thermotropic poly(ester-carbonates) and poly(ester-imides), may all be synthesized in a similar manner. 

The industrial challenge ahead will be to define and develop applications which take advantage of the unique properties of aromatic thermotropic polyesters. Already, commercial demand is growing in the fiber optic, chemical process, electrical/electronic, automotive and houseware markets, and new areas of potential application continue to emerge. 

The synthesis and characterization of a full aromatic thermotropic liquid crystalline poly (aryl ether ketone) with pendant chlorine group (CIPAEK)... 

One of the initial motivations for developing thermotropic LCPs was the search for high-tensile-performance fibres with properties similar to those exhibited by DuPont s Kevlar , a lyotropic LCP [3]. As polymer developments continued, the wholly aromatic, thermotropic polyesters were found to offer useful properties in addition to excellent tensile capabilities, especially as engineering thermoplastics [4]. 

Wholly aromatic thermotropic polyesters were developed soon after by Celanese, who defined families of copolymers based on 2,6-naphthalene... 

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