Thermotropic aromatic poly ester-amides

Work with NDA, OHN and HNA monomers has also led to the development of thermotropic aromatic poly(ester-amides). The question arose as to whether the introduction of hydrogen bonding capability into the chain might result in some useful property improvements. The greater interchain interaction could result in increased fiber fatigue resistance, higher filament Shear modulus (and tensile modulus) and improved fiber surface adhesion. Early data are promising, but considerable research remains before the potential of the ester-amide variants can be fully defined. 

J.D. Sudha, Synthesis and characterization of hydrogen-bonded thermotropic liquid crystalline aromatic-aliphatic poly(ester-amide)s from amido diol, J. Polym. Sci. A Polym. Chem. 38 (2000) 2469-2486. 

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. 

Aromatic imide groups are known to be nearly planar, rigid, polar, and thermostable. However, aromatic imide structures are also known to be non-mesogen in nature. Poly(ester-amide) (PEI) derived from N- (4 -carboxyphenyl) trimellitimide and aliphatic spacers are not thermotropic, whether the spacer used is chiral or not. Semi-aliphatic spacers are observed to exhibit both a smectic and a nematic LC phase in the resultant thermotropic PEIs. The semi-aliphatic chiral spacers exhibit both chiral smectic phase (A or C ) and cholesteric phase. Such a chiral smectic LC-phase, which may be ferroelectric in nature, is extremely rare for LC-main-chain polymers [27]. It is a particular advantage of polar imide mesogens to favor the formation of layer-structures when combined with non-polar species [28]. 

De Candia F, Renzulli A, Vittoria V, Roviello A, Sirigu A (1990) Transport properties of a thermotropic liquid-crystalline polyester. J Polym Sci Part B Polym Phys 28 203-211 East AJ, Charbonneau LF, Calundann GW (1982) Poly(ester-amide) capable of forming an anisotropic melt phase derived from 6-hydroxy-2-naphthoic acid, dicarboxylic acid, and aromatic monomer capable of forming an amide linkage. US Patent 4,330,457, 18 May 1982 Fellahi S, Meddad A, Fisa B, Favis BD (1995) Weldlines in injection-molded parts a review. Adv Polym Technol 14 169-195... 

Completely rigid rod-like molecules such as poly(4-oxybenzoyl) or poly( p-phenylene terephthalate) tend to be highly crystalline and intractable, with melting points above the decomposition temperature of the polymers (>450°C). The problem of thermotropic MCLCP design is to disrupt the regularity of the intractable para-linked aromatic polymers to the point at which mesomorphic behaviour is manifested below the decomposition temperature and the materials can be processed in fluid yet ordered states. The disruption must not, however, be taken to the stage where conventional isotropic fluid behaviour is preferred. These requirements that the polymer must retain some rod-like nature but at the same time be melt-processable below 400-450°C have limited thermotropic MCLCPs mainly to polymers based on the linear ester or ester/amide bonds. With polyester/ polyesteramides, disruption is normally achieved by the th ee copolymerization techniques outlined in Fig. 8.1, i.e. frustrated chain packing, flexible spacers and non-linear links. 

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