Hydroxynaphthoic acid copolyester

Abstract Recent progress on elucidating the role of interchain transesterification reactions in the copolyesters is described. New data are presented supporting the chemical nature of the ordering process. An unexpected degradation reaction in the p-hydroxybenzoic acid/2,6-hydroxynaphthoic acid copolyester system is discussed. 

Poly(p-phenylene terephthalamide (Kevlar) (b) copolyester of p-hydroxybenzoic acid and biphenylene terephthalate (Xydar) (c) copolyester of p-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid (Vectra). 

It was later confirmed by Ide and Chung [119] that these observations were also valid for thermotropics. Small-diameter rods of a longitudinal PLC (a copolyester based on 2,6-hydroxynaphthoic acid, terephthalic acid and p-aminophenol) were annealed above its crystal melting temperature in the nematic state for different periods of time. The dependence of the Young modulus at room temperature on the... 

Early studies of the thermal degradation of so-called polyarylates were covered by Neiman [100] and Ehlers and co-workers [101]. Since then, several highly aromatic and specifically liquid crystalline (mesogenic) polyesters have been examined in terms of their anaerobic thermal degradation characteristics. These inclnde homopolymers of hydroxybenzoic acids [102-105] copolymers of hydroxybenzoic acid with hydroxynaphthoic acid [105-108] polymers which are essentially copolymers of hydroxybenzoic acid and alkyene terephthalates [107-118] copolymers of hydroxybenzoic acid with other aromatic polyesters [119-122] phenolic and bisphenolic terephthalates [123-127] poly(oxynaphthoate)s [128] and liquid crystal polyesters (LCP) containing unsaturated acids as part of a copolyester chain [129-131]. 

Vectra A Liquid crystal polymer, LCP reinforced or not a copolyester from hydroxy benzoic acid with hydroxynaphthoic acid Hoechst Celanese Corp. 

Materials. Three thermotropic LCPs have been used in our studies. Vectra A900, an aromatic copolyester of 1,4-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid, and Vectra B950, a copolymer of 2,6-hydroxynaphthoic acid, 4-aminophenol and terephthalic acid, were supplied from the Hoechst Celanese Corporation. Both LCPs possess a melt temperature of 280 C. Rodrun LC3000, supplied by Unitika, is a copolymer of polyethylene terephthalate (PET) and 1,4-hydroxybenzoic acid, and possesses a melt temperature of 220 C. 

The first melt-processable (later categorized as thermotropic liquid-crystalline) polymer, based on p-hydroxybenzoic acid and biphenol tereph-thalate, was reported by Steven Cottis in 1972. This polymer is now available on the market as Xydar . In 1973, the first well-characterized thermotropic polymer, a copolyester of p-hydroxybenzoic acid and ethylene terephthalate, was patented by Herbert Kuhfuss and W. Jerome Jackson (Eastman-Kodak Co., USA). They reported the discovery of liquid-crystalline behaviour in this polymer in 1976. At the beginning of the 1980s, the Celanese Company developed a family of processable thermotropic liquid crystalline polymers based on hydroxybenzoic acid and hydroxynaphthoic acid, later named Vectra . 

Figure 6.22 Apparent melt viscosity as a function of shear rate at 350°C for polyethersulphone (PES) and liquid crystalline Vectra A950 (copolyester based on p-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid). Drawn after data from Engberg et al (1994a).

Copolymerization is one of the most efficient synthetic techniques to decrease the crystallinity and melting temperature of a given polymer. The melting-point depression occurring in copolyesters (Vectra) based on p-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid (HNA) is in fact relatively moderate in comparison with that of other copolymers (Fig. 6.35). The minimum in melting point occurs at about 40 mol% HNA. The decrease in isotropization temperature in the copolyesters is moderate, leading to the desired expansion of the temperature region of a nematic phase. 

Kachidza J, Serpe G, Economy J (1992) Ordering processes in the 2,6-hydroxynaphthoic acid (HNA) rich copolyesters of p-hydroxybenzoic acid and HNA. Makromol Chem Macromol Symp 53 65-75... 

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