Liquid Crystal Polymers. XI. Liquid Crystal Aromatic Polyesters: Early History and Future Trends

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Abstract
This brief history and review of liquid crystalline polyesters (LCPs) is limited to all-aromatic LCPs except for a description of the discovery of the first thermotropic polymer to be injection molded or melt spun and characterized as being liquid crystalline: an Eastman PET/PHB (p-hydroxybenzoic acid) copolyester (first reported as being liquid crystalline in 1974). In the same year a Carborundum terephthalic acid/4,4′-biphenol/PHB all-aromatic copolyester was reported to be injection moldable, and later this polymer was shown to be liquid crystalline. In 1975 various Du Pont LCPs prepared with substituted hydroquinones were disclosed, and in early 1978 the first Celanese LCPs based on 2,6-oriented naphthalene monomers were disclosed. The development and characterization of all-aromatic LCPs up to 1987 are described, with the LCP classification based on the following monomers: 4,4′-biphenol; asymmetrically substituted monomers; 2,6-oriented naphthalene monomers; 3,4′-oriented benzophenone and diphenyl ether monomers; and kinking monomers. The commercial LCPs are also briefly described and future trends are discussed.