Liquid crystalline copolyester and

Kinetics of Phase Segregation in Thermotropic Liquid-Crystalline Copolyester and Polyether Imide Blends... 

PRELIMINARY THERMAL AND STRUCTURAL STUDIES OF BLENDS BASED ON A THERMOTROPIC LIQUID CRYSTALLINE COPOLYESTER AND POLY(ETHYLENE) TEREPHTHALATE... 

The elastic moduli of an extruded PLC are largely determined by its molecular orientation, so we first consider the orientation parameters calculated from the observed meridional X-ray reflections. For liquid crystalline copolyesters and copolyesteramides, the sharpness of these reflections gives an indication of the coherence length, a value corresponding to 10 monomers being typical. Therefore, the orientation parameter obtained from the meridional reflection is not specific to the crystalline regions but instead reflects the average orientation of all the chains in the polymer. 

Blackwell J, Biswas A, Cheng HM, Cageao RA (1988) X-ray Analysis of Liquid Crystalline Copolyesters and Copolyamides. Molecular Cryst Liq Cryst 155 299-312. 

Liquid crystalline behavior affects the melt viscosity of the polymer and the ability of the polymer to retain the ordered arrangement in the solid state. Thus, liquid crystaUine behavior during the melt results in lower viscosity because the rigid polymeric mesophases align themselves in the direction of the flow. As a result, the polymer is easier to process. Also, retention of the arrangement upon cooUng yields a material with greatly improved mechanical properties. Several thermotropic liquid crystalline copolyesters and polyamides are available commercially. 

The compatibility between some thermotropic liquid crystalline copolyesters and other isotropic polyesters, such as poly(ethylene terephthalate) [86-90], poly(butylene terephthalate) [91-94], poly(ethylene naphthalate) [95],... 

Skin/core morphologies are common in blends of LCP s and thermoplastic polymers and they play a significant role in defining the properties of both extruded and injection molded samples. Usually, LCP s in the skin have a higher degree of orientation than in the core when the blends are extruded or injection molded (Husman et al. 1980 Hedmark et al. 1989 Lee 1988). Baird et al. (Baird and Mehta 1989 Baird and Sukhadia 1993) observed a skin/core morphology in blends of PA 66 with HBA/HNA and 40 PET/60 PHB and 20 PET/80 HBA copolyesters. More LCP fibers were present in the skin than in the core for both systems. Isayev and Swaninathan (1994) also reported shell-core structure in the fracture surfaces of injection molded blends of HNA/HBA liquid crystalline copolyesters and poly (etherimide). 

Joseph, E. G., Wilkes, G. L., and Baird, D. G., Preliminary thermal and structural studies of blends based on a thermotropic liquid crystalline copolyester and poly(ethylene terephtalate), Polymeric Liquid Crystals (A. Blumstein, ed.. Plenum Press, New York, 1985, p. 197. 

Figure 17 Differential scanning colorimetric trace of the liquid crystalline copolyester of 8-(3-phenyl hydroxy) octanoic acid and paro-hydroxy benzoic acid.

Various process steps were used to determine their Influence on the morphological nature of liquid crystalline copolyester films. Compression molding was used to form quiescent films, while extenslonal deformation above and below the onset of fluidity, as well as shear deformation above the onset of fluidity was used to make non-quies-cent films. It Is a basic result that molecular orientation can only be achieved when the deformation is done while the polymer is In a liquid crystalline melt state. Experimental details are given In the subsection Materials and Processing, while an interpretation is offered in the discussion in the subsection Morphological and Process Consideration. ... 

A few series of azo and azoxy group containing liquid crystalline copolyesters were prepared by limura and coworkers and their phase transition temperatures were examined. No unusual phenomena were found, although monotropic mesophases were observed for the following copolyesters, depending on the combinations and fractions of alkylene groups ... 

In a previous paper (1), phase segregation by spinodal decomposition in mixtures of polyethylene terephthalate and polyhydroxybenzoic acid copolymer (PET-PHB) and polycarbonate (PC) has been investigated. It was shown that thermally induced phase segregation takes place above the Tg of PC and exhibits a lower critical solution temperature (LCST). However, the phase separated domains do not grow until the temperature exceeds 255°C. Some disclinations developed within the liquid crystal rich regions. Even in the pure PET-PHB component, four dark brushes with negative sense of disclinations form around 240°C, indicating the presence of nematic liquid crystals. Paci and coworkers (2) claimed that a smectic-nematic transition exists near 270°C in this liquid crystalline copolyester. 

A forced mixture of PET with a liquid-crystalline copolyester (LCP) of ethylene terephthalate and... 

J. L. Brewbaker and W. B. Marshall. Liquid crystalline copolyesters of 4-hydroxybenzoic acid and substituted 4-hydroxybenzoic acids. US Patent 5 268 443, assigned to The Dow Chemical Company (Midland, Ml), December 7, 1993. 

W. Grasser, H.-W. Schmidt, and R. Giesa. Fibers spun from poly(ethyl-ene terephthalate) blended with a thermotropic liquid crystalline copolyester with non-coplanar biphenylene units. Polymer, 42(21) 8517-8527, October 2001. 

R Sukananta and S. Bualek-Limcharoen. In situ modulus enhancement of polypropylene monofilament through blending with a liquid-crystalline copolyester. J. Appl. Polym. Sci., 90 1337-1346, 2003. 

S. Saikrasun, S. Bualek-Limcharoen, S. Kohjiya, and K. Urayama. Thermotropic liquid-crystalline copolyester/thermoplastic elastomer in situ composites. I. Rheology, morphology, and mechanical properties of extruded strands. J. Appl. Polym. ScL, 89 2676-2685, 2003. 

S. Saikrasun and T. Amomsakchai. Phase behavior and properties of in situ-reinforcing elastomer composites based on thermoplastic elastomers and thermotropic liquid crystalline copolyester. J. Appl. Polym. ScL, 101 1610-1619, 2006. 

S. C. Tjong, R. K. Y. Li, and X. L. Xie. Compatibilizing effect of styrene-maleic anhydride copolymer on the properties of polyamide-6/liquid crystalline copolyester composites. J. Appl. Polym. ScL, 77 1964-1974,2000. 

HBA/PET 80/20 a liquid crystalline copolyester composed of 80 mole percent p-hydroxy-benzoic acid [HBA] and 20 mole percent PET. 

Blizard, K. G., and D. G. Baird. 1987. The morphology and rheology of polymer blends containing a liquid crystalline copolyester. Polymer Engineering and Science 27 653-662. 

Although the monomers 1-V contain preset monomer sequences, they are destroyed and randomized during polymerization at elevated temperatures, leading to the formation of random copolyesters. Such randomizations were proved to occur in the preparation of other liquid crystalline copolyesters[4,5]. Moreover, utilization of high molecular weight monomers minimizes the loss of reactants through volatilization during polymerization. 

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. 

Wang Jiu-fen, Zhang Na., Li Cheng-Jie. (2005). Synthesis and Study of Thermotropic Liquid-Crystalline Copolyester. PABA.ABPA.TPA. Polym. Mater. Sci. Technol, 21(1), 129-132. 

Dong Dewen, Ni Yushan, Chi Zhenguo. (1996). Synthesis and Properties of Thermotropic Liquid-Crystalline Copolyesters Containing Bis-(4-oxyphenyl)Methanone. II. Copolyesters from Bis-(4-oxyphenyl)Methanone, Terephthalic Acid, n-oxybenzoic Acid and Resorcene. Po/>wi. (2), 153-158. 

Teoh, M. M., Liu, S. L., Chung, T. S. (2005). Effect of Pyridazine Structure on Thin-Fihn Polymerization and Phase Behavior of Thermotropic Liquid Crystalline Copolyesters. J. Polym. Sci. B, 43(16), 2230-2242. 

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