Naphthalene diol/polyester,

Attempts had been made to synthesise polyesters based on phthalic acid as the diacid component, but these products were amorphous, had low softening points, and were rapidly attacked by organic solvents and acids and bases. Research into polyesters made by the reaction of terephthalic acid (or esters thereof) with aliphatic diols, led to the discovery of polyesters of high commercial value poly(alkylene terephthalate)s [4]. This pairing of diols with terephthalic acid eventually led to the most commercially successful aromatic polyesters, but other synthetic pathways were also investigated towards such products in the early days of polyester development. These included the self-condensation of hydroxy acids of the structure -H0-R-Ph-C02H, where R-OH is para to the acid group and R is -(CH2)- or -(CH2)2- [5], and reactions of aliphatic diacids with 1,4-dihydroxy benzene and similar aromatic diols [6, 7]. Also synthesised about the same time were polyesters based on C2-Cg aliphatic diols and any of the isomeric naphthalene dicarboxylic acids [8]. 

Versions with diacid, diol and di-ester substituents have been patented [111] which are suitable for reacting into aromatic polyesters, as have stabilisers with suitable substituents to allow dispersion or dissolution in dye baths for impregnation into fibres or textiles [113,114,116]. Other related species include those with biphenylene groups on the 4- and 6-positions on the triazine core [119], naphthalene groups on 4 or on both 4 and 6 [120], 1,2,3,4-tetrahydronaphthalene on 4 and 6 [124], and 2-hydroxynaphthalene on the 2-position [125]. Versions with longer side chains than hexyl or octyl have also been synthesised, and it is claimed that these have increased compatibility with their host polymer [121, 127]. 

N. Khan, Z. Bashir, and D. M. Price, Liquid crystalline aromatic polyesters formed with terephthalic acid, phenyl hydroquinone, and naphthalene or anthracene diols. Journal ( Applied Polymer Science, 58,1509 (1995). 

The aromatic semiflexible polyesters can be formed by varying the dicarboxylic multi phenyl acid structure (naphthalene and diphenol) and non-linear aromatic diol (3,4 -dihydroxybenzophenone). 3,4 -dihydroxybenzophenone can be synthesized from 4-methoxy bromobenzene and m-methoxybenzonitrile via multistep reaction, which can be condensed with respective diacid chloride in o-dichlorobenzene at reflux temperature [43]. It is well known that dimethyl siloxane spacer can make a flexible/semiflexible LC polymer. Thermotropic flexible liquid-crystalline main chain polyesters... 

Polyester fibres, as described in this chapter, are based on terephthalic acid with different glycols like butane diol, propylene glycol, with the most common being ethylene glycol (EG) as shown in Figure 10.1. Polyesters based on other acids like naphthalene dicarboxylic acid (PEN fibres) or lactic acid (PLA fibres) are different products. 

Unstable prepolymer systems are represented by the Vulkollan process. A prepolymer is first prepared by reacting polyol with an excess of diisocyanate typically at about HO C. In the specific case of Vulkollan the polyol is an aliphatic polyester of molecular weight c. 2000, and the isocyanate is 1,5-naphthalene diisocyanate. Because this isocyanate tends to become involved in side reactions leading to cross-linking the prepolymer is unstable. It has thus to be used within a few minutes of preparation by mixing with a chain extender, typically butane diol, and cast into a mould. A subsequent hot air cure for 24 hours at 100°C is desirable to obtain optimum properties. 

Although PET and PBT are widely used, better thermal and mechanical properties are desired for some applications. Higher performance in semiaromatic polyesters was obtained from polyalkene naph-thalates. These semicrystalline polyesters are prepared by the condensation polymerization of naphtha-lene-2,6-dicarboxylic acid and flexible aliphatic diols. The naphthalene moiety imparts stiffness to the linear polymer backbone, leading to improved physical and mechanical, barrier, chemical resistance properties, and UV-ray screening performance. Poly(ethylene naphthalene-2,6-dicarboxylate), PEN, became commercially available from Teijin Ltd. in the early 1970s. PEN has a Tg and of 125 and 268°C, respectively [34]. Its structure appears in Fig. 1.18. 

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