Liquid crystal copolyesters terephthalic acid

Liquid crystal copolyesters have been synthesized [50-56] on the basis of -acetoxybenzoic acid, acetoxybisphenol, terephthalic acid and... 

Liquid crystal copolyesters have been S5rnthesized [50-56] on the basis of -acetoxybenzoic acid, acetoxybisphenol, terephthalic acid and m-acetoxybenzoic acid by means of polycondensation in melt. All the copolyesters are thermotropic and form nematic phase. The t5rpes of LQPs of -oxybenzoic acid are given in Table 7.2. 

In a previous paper (1), phase segregation by spinodal decomposition in mixtures of polyethylene terephthalate and polyhydroxybenzoic acid copolymer (PET-PHB) and polycarbonate (PC) has been investigated. It was shown that thermally induced phase segregation takes place above the Tg of PC and exhibits a lower critical solution temperature (LCST). However, the phase separated domains do not grow until the temperature exceeds 255°C. Some disclinations developed within the liquid crystal rich regions. Even in the pure PET-PHB component, four dark brushes with negative sense of disclinations form around 240°C, indicating the presence of nematic liquid crystals. Paci and coworkers (2) claimed that a smectic-nematic transition exists near 270°C in this liquid crystalline copolyester. 

Jackson and Kiitifuss reported a thermotropic liquid crystalline polymer which was a copolyester of poly(ethylene) terephthalate (PET) and parahydroxybenzoic acid (PHB). In this copolyester, PET has a flexible chain conformation while PHB has a stiff, rod-like conformation and the polymer is indicated to be the liquid crystal forming component. Schematically, this copolyester... 

In Figure 16, results of Jackson and Kuhfuss show the effect of molding temperature and polymer morphology weight on the mechanical properties for poly(ethylene terephthalate) modified with p-hydroxybenzoic acid. "The temperature at which the PHB copolyesters are injection molded affects the orientation of the liquid-crystal polymer chains and, therefore, affects the mechanical properties. 

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]. 

Liquid-crystal aromatic copolyesters (LCP) were studied. They were derived from dioxydiphenyl diacetate, acetoxybenzoic, iso- and terephthalic acids (IPA and TPA, respectively) 100/0, 75/25, 50/50, 25/75, 0/100. 

These thermotropic liquid-crystalhne polymers have high melting points but can be melt-processed like other thermoplastics. The macroscopic orientation of the extended-chain crystals depends on the orientation imparted by flow during processing (molding, extrusion, etc.). Because of the fibrous nature of the extended-chain crystals, these plastics behave as self-reinforced composites, with excellent mechanical properties, at least in the chain direction. This is illustrated in Table 4.3 for molded specimens of a hquid-crystalline copolyester of ethylene glycol, terephthalic acid, and / -hydroxybenzoic acid [14]. In the direction parallel to the flow, the properties listed in Table 4.3 favorably compare with ordinary crystalline thermoplastics (nylons, polyesters) reinforced with up to 30% glass fibers. 

The next development in liquid crystal polyesters was the preparation by polycondensation based on terephthalic acid (TPA) and hydroquinone (HQ) or p-hydroxybenzoic acid (HBA). The polyesters are insoluble with very high melting temperatures of 600 °C for poly (TPA/HQ) and 610 °C for poly (HBA), which are by far too high to obtain stable liquid crystalline phases for melt processing. In 1972, Economy and coworkers patented several copolyester compositions, and one of these are the copolymerization of poly (4-hydroxybenzoic acid) (PHB) with 4,4 -dihydroxybiphenyl (BP) and terephthalic acid (TPA) due to the need for lower melting, melt-processable polymers. Considerable synthetic efforts have been attempted in order to decrease the melting temperatures of aromatic LC polyesters while retaining LC properties. The copolyester structure was tailored by partial substitution of TPA with isophthalic acid to produce a melt-spinnable material. 

Issam AM, Mohd Fadhley A, Wan Rosli WD (2012) New class of liquid crystalline epoxy resins synthesis and properties. J Ind Eng Chem 18 364—372 Jackson WJ Jr, Kuhfuss HF (1976) Liquid crystal polymers. I. Preparation and properties of p-hydroxybenzoic acid copolyesters. J Polym Sci Polym Chem Ed 14(8) 2043-2058 Karayannidis GP, Archilias DS, Sideridou ID, Bddaris DN (2005) Alkyd resins derived from glycolized waste poly (ethylene terephthalate). Eur Polym J 41 201-210 Marin L, Cozan V, Bruma M (2006) Comparative study of new thermotropic polyazines. Polym Adv Technol 17 664—672... 

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