Thermotropic copolyesters

Most of the work to date concerns the area with the greatest potential for commercial exploitation, the blending of LCPs with conventional polymers. While a few studies of solution blending with Kevlar do exist [57-61], most of the work has centered on melt blending thermotropic copolyesters (Vectra, Xydar) with engineering thermoplastics (PET, PC, PEI, etc.). For convenience, this work may be separated into three blend regions based on LCP content, namely ... 

Main Chain LC Polymers. New thermotropic copolyesters with either random or ordered mesogenic sequences have been reported with a wide range of mesophase behaviors. Recent developments in this field have included the use of naphthalene, stilbene and related structures in addition to the traditional phenylene groups to produce the required rigid main chain, and these are described in chapters by Jin, Jackson and Morris, and Skovby et al. Efforts have been undertaken to control transition temperatures and solubility through the use of either substituents or changes in the monomer sequence distribution. Successful application of these efforts have led to the commercialization of several thermotropic aromatic copolyesters (23.24). 

This paper is concerned with the idea of generating films which are reinforced on an in-situ basis by means of the addition of thermotropic copolyesters. 

Xue Y, Kara M, Yoon HN (1998) Ionic naphthalene thermotropic copolyesters divalent salts and tensile mechanical properties. Macromolecules 31 7806-7813... 

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. 

Figure 5.3. Representative structures of three types of thermotropic copolyesters.

A more detailed study verified that PBLG/m-cresol solution and thermotropic copolyester under shear rate exhibits negative first normal stress difference, i.e., the difference between normal stresses parallel and perpendicular to the flow direction, as shown in Figure 6.18. 

Windle AH, Viney C, Golombok R, Donald AM, Mitchell GR (1985) Molecular correlation in thermotropic copolyesters. Faraday Disc. Chem. Soc., 79 55 see also following discussion pp.100-123... 

It is reported [403] on liquid-crystal polyenamineketone and on mix of liquid-crystal thermotropic copolyester with polyketone [404]. The mix is prepared by melts mixing. It has been foimd that the blending agents are partially compatible the mixes reveal two glass transition temperatures. 

Blackwell, J., Dutierrez, G., Chivers, R. (1985). X-ray Studies of Thermotropic Copolyesters in Proceedings of the 2nd Symposium Div. Pofym. Chem. Polym. Liq. Ciyst. Washington E)C, New York, London, 167-181. 

Windle, A., Viney, C., Golombok, R. (1985). Molecular Correlation in Thermotropic Copolyesters Faraday Discuss. Chem. Soc, 79, 55-72. 

Hsiue Lin-tee, Ma Chen-chi M., Tsai Hong-Bing. (1995). Preparation and Characterizations of Thermotropic Copolyesters of p-hydroxybenzoic Acid, Sebacic Acid, and Hydroquinone. J. Appl. Polym. Sci., 56(4), 471 76. 

Shinn Ted-Hong, Lin Chen-Chong, Lin David, C. (1995). Studies on Co [Poly( Ethylene Terephthalate-p-oxybenzoate)] Thermotropic Copolyester Sequence Distribution Evaluated from TSC Measurements. Polym, 36(2), 283-289. 

Takase, Y, Mitchell, G., Odajima, A. (1986). Dielectric Behavior of Rigid-Chain Thermotropic Copolyesters. Polym. Commun, 27(3), 76-78. 

Ericksen proposed a theory for fluids such as nematic liquid crystals which could become anisotropic during flow. By assuming symmetry around the director, the expression for the stress tensor was somewhat simplified. We compare here briefly Ericksen s transversely isotropic fluid theory with the transient behavior observed for thermotropic copolyesters of PHB/PET. 

Table 4.4 Processing parameters and mechanical properties for injection molded thermotropic copolyester of 60 mol% p-acetoxybenzoic acid, 20 mol% terephthalic acid and 20 mol% naphthalene. (Reprinted with permission from [21], copyright 1983 Society of Plastics Engineers, Inc.)...

Hierarchical systems were introduced in section 9.5. It is possible to treat these systems quantitatively [58,64,65]. George and Porter [64], for example, have mixed a monomolecular liquid crystal (MLC), i.e. a low molar mass molecule, with a thermotropic copolyester of the Kuhfuss and Jackson type [10]. They found that it was possible to describe the melting behavior of their system with reasonable accuracy by equation (9.9), although that has been derived by Flory [66] for... 

The phase diagrams of ternary systems consisting of a thermotropic copolyester as described above, a random coil polymer and a solvent have been treated by Blonski et al. [65], who also applied statistical thermodynamics. These systems are of interest because they show an isotropic mixture in a certain concentration range (Figure 9.24). 

For most of the results discussed below, the following is valid concerning COP, PC and mixtures if not otherwise stated. The thermotropic copolyester derived from p-hydroxybenzoate and poly(ethylene terephthalate) [10] containing 60 mol% PHB was used exclusively as the PLC component because this composition has the best mechanical properties [10,118] of these copolymers. It was obtained from Eastman Kodak, Kingsport, TN, and had an average molar mass estimated from solvent viscosity of about 19000 g mol . The sequence distribution was calculated from C-NMR as described by Lenz et al. [119] and was nearly random the statistical parameter which describes the randomness of the copolymer is = 1 for a block copolymer and P = 0 for a completely random copolymer. The copolymer used for the experiments had P = 0.15. 

Cheng SZD (1988) Kinetics of mesophase transitions in thermotropic copolyesters. 1 calorimetric study. Macromolecules 21 2475... 

Random copolymerization is an effective way to disturb the regular molecular structure of the polymer chain. The lack of periodicity along the chain inhibits crystallization and, thus, reduces the crystal size and perfection and depresses Tm. If the chosen comonomer is essentially linear, losses of chain mesogenicity can be minimized. This approach has been followed in designing thermotropic copolyesters, such as Vectra A by Celanese (now Ticona), which continues to enjoy commercial success. Vectra A is the copolyester of p-acetoxybenzoic acid (ABA) and 2,6-acetoxynaphthoic acid (ANA) with a mole ratio of 73/27. The melting point of this LCP is around 280°C, which is much lower than the melting points of the either poly (ABA) or poly (ANA) [6]. 

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