Methoxy substituents, polyesters

There is a wide diversity of chemical structures of anthraquinone colorants. Many anthraquinone dyes are found in nature, perhaps the best known being alizarin, 1,2-dihydroxyanthraquinone, the principal constituent of madder (see Chapter 1). These natural anthraquinone dyes are no longer of significant commercial importance. Many of the current commercial range of synthetic anthraquinone dyes are simply substituted derivatives of the anthraquinone system. For example, a number of the most important red and blue disperse dyes for application to polyester fibres are simple non-ionic anthraquinone molecules, containing substituents such as amino, hydroxy and methoxy, and a number of sul-fonated derivatives are commonly used as acid dyes for wool. 

Later workers, chiefly in Japan, used naphthalimides with alkoxy substituents at the 4- or 4,5-positions and obtained brighteners with good lightfastness for polyester substrates and good chlorite fastness for polyacrylonitriles. The first commercial product was 4-methoxy-iV-methylnaphthalimide (64) [3271-05-4] [113], Table 7.10 lists the most important compounds. 

A selection of monosubstituted and disub-stituted poly-(/ -phenylene-terephthalate)s is compared in Table 2. Poly(p-phenylene-terephthalate)s with methyl, methoxy, chlo-ro, or bromo substituents on either the hy-droquinone or the terephthalic acid moiety exhibit melting temperatures of 350 °C or higher. Thermotropic liquid crystalline behavior is observed in these samples, although it is in the range of thermal decomposition. A comparison of the mono- and diphenyl substituted polyesters reveals an important trend. The monosubstituted poly-(p-phenylene-terephthalate) with the phenyl substituent in the hydroquinone moiety melts at 346 °C, also forming a nematic melt up to a clearing temperature of... 

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