Hydroquinone terephthalate

A typical example of a small liquid crystalline molecule, derived from terephthalic acid and the ethyl ether of hydroquinone, has a liquid crystalline range between 215 and 267 C. However, the liquid crystalline polymer, hydroquinone terephthalate, is so high melting (above 600°C) that it decomposes before exhibiting a transition from the crystalline to the liquid crystalline state.1... 

The homopolymer has a melting temperature of at least 550° C. It is insoluble in all known solvents and is exceptionally thermally stable. The metal-like polymer, however, can only be worked by hammering, sintering, or plasma spraying. For this reason, more easily processed copolymers of p-hydroxybenzoic acid with isophthalic acid, hydroquinone, terephthalic acid, orp,p-diphenyl ether with correspondingly changed mechanical properties have been made. Industrially, these polymers are often referred to briefly as aromatic polyesters. ... 

Instead of attaching a large substituent, phenyl, to the hydroquinone molecule to reduce the high melting points of hydroquinone terephthalate polyesters, flexible aliphatic components can be incorporated in the polymer chain. In our earlier paper,we noted that the polyester of 4,4 -(ethylenedioxy)dibenzoic acid and hydroquinone (II, n=2, R=H) melted at... 

The strueture and properties of various liquid-crystal copolymers are studied in Refs. [107-112]. For example, copolymers based on n-oxybenzoie aeid, polyethyleneterephthalate, hydroquinone and terephthalic acid, ate studied in Ref. [107] the introduetion of the mix hydroquinone/terephthalic acid accelerates the proeess of erystallization and increases the degree of crystallinity of polyesters. 

Other TLCPs, such as copolyesters of HBA and 6-hydroxy-2-naththoic acid (HNA) (Calundann 1978, 1979, 1980), and copolyesters of 4,4 -bisphenol (or hydroquinone), terephthalic acid, and HBA (Cottis et al. 1972, 1976) have also been synthesized and commercialized. For instance, copolyesters consisting of HBA and HNA have the following chemical structure ... 

LC Poly(butadiene) +p-nitrostilbene LC Poly(hydroquinone terephthalate), f-butyl LC Poly(norborene) +p-nitrostilbene LC Polylster... 

The polyester made by reacting hydroquinone with terephthalic acid also melted above 500°C. That from bis-phenol A and 4,4 -(2,2-butylidene)dibenzoic acid is said to be stable in nitrogen to above 400°C. 

For the liquid crystal polyesters the basic structural units are derived from such materials as 5-hydroxybenzoic acid, terephthalic acid and hydroquinone. Some basic sequences from such materials are shown in Figure 25.25. 

Many researchers have reported the structure-thermal property correlations in LCPs from substituted hydroquinones (HQs) and dicarboxylic acids. Lenz and co-workers have investigated the liquid crystallinity of the polyarylates obtained from substituted HQs and terephthalic acid (TA) [6-10], substituted HQs and l,10-bis(phenoxy)decane-4,4/-dicarboxylic acid [8], and substituted HQs and a,oo-bis(phenoxy)alkane-4,4/-dicarboxylic acid [11], Kricherdorf and Schwarz [12] and Osman [13] reported the liquid crystallinity of the polyarylates obtained from substituted HQs and 1,4-cyclohexanedicarboxylic acid, while Krigbaum el al. [14], Heitz and co-workers [15] and Kricherdorf and Engelhardt [16] investigated the liquid crystallinity of the polyarylates synthesized from substituted HQs and substituted TAs. In addition, Jackson reported the liquid crystallinity and the moduli of fibers and injection molded specimens of the polyarylates... 

E4 poly[(4-hydroxybenzoic acid)-co-hydroquinone-co-(terephthalic acid)]... 

Keywords anhydrous hydrazine, hydroquinone, dimethyl terephthalate, inclusion crystal, terephthalic acid dihydrazide... 

A mixture of powdered dimethyl terephthalate la (19.4 g, 0.1 mol) and 1 1 inclusion complex of hydroquinone and hydrazine (58.5 g, 0.4 mol) was kept under a nitrogen atmosphere at 100-125 °C for 25 h. To the reaction mixture was added MeOH and MeOH insoluble terephthalic acid dihydrazide 2a was obtained by filtration (17.1 g, 88.1% yield). 

The most effective catalysts are mixtures of diethylzinc and an equimolar amount of a compound containing two active hydrogen atoms — e.g., water, resorcinol, hydroquinone or terephthalic acid. Mixtures of Zn t2 with compounds having only one active hydrogen are ineffective at any molar ratio. The catalysts thus appear to have a polymeric structure. 

AO containing various phenolic moieties were prepared by transesterification in the presence of tetraalkyl titanates. Randomly distributed -active moieties are characteristic of 140 (only the hard polyester segment is given) prepared from dimethyl terephthalate, 1,4-butanediol, poly(tetramethylene oxide)diol and dimethyl 5-(3,5-di-tm-butyl-4-hydroxybenzenepropaneamido)isophthalate [181]. The mentioned polymeric AO was used for stabilization of polyether-polyester elastomers. A partial attachement of tetrakis[methylene 3(3,5-di-tert-butyl-4-hydroxy-phenyl)propionate]methane (3) via transesterification reaction was expected in the synthesis of another polyether-polyester elastomer by [182]. A reversible redox polyester was formed from 2,5-bis(2-hydroxyethyl)hydroquinone and dichlorides of aliphatic dicarboxylic acids [137],... 

The chiral side chain polymers derived from asymmetric esters of terephthalic acid and hydroquinone can form (in a broad temperature range, including ambient temperature) an unusual mesophase (the isotropic smectic phase, IsoSm ) characterized by high transparency and optical isotropy within the visible wavelength range, combined with a hidden layered smectic ordering and some elements of helical superstructure at shorter dimensions of 10 to 250 nm. The short-pitch TGB A model seems to be the most adequate for the mesophase structure. 

Cyclic dimer (0.1). terephthaiic acid (0.5). benzoic acid (6). hydroquinone (40.5). and various fragments of the main chain benzene, phenol, benzaldehyde. biphenyl, benzoquinone. 4-hydrox henylbenzoate. benzoic aod. mono and di(4-hydroxyphenyl) terephthalate. terephihaNc add. terephthaldehydic add. short cham fragments... 

Hydroquinone(HQ) or a naphthalenediol in the above reactions can be replaced with other diols such as biphenols and bisphenols. In the same manner, other dicarboxylic acid such as cyclohexane dicarboxylic acid, isophthalic acid, naphthalene dicarboxylic acids can be used in place of terephthalic acid. Of course, these substitutes should not destroy the linearity of the polymer chains if one is to obtain thermotropic compositions. 6-Hydroxy-2-naphthoic acid is a substitute for 4-hydroxybenzoic acid in Reactions 18 and 19. 

The synthetic scheme used for the preparation of the LC polymers reported here involves the random copolymerization of both aromatic and aliphatic components as shown in Fig. 1. Both the diol and hydroquinone components can react with nearly equal probability with the diacid chloride component. We therefore have three factors which can contribute to inhomogeneity in this polymer system (i) the polydispersity of chain length expected in a condensation polymerization, (ii) the distribution of diol and hydroquinone components in the polymer chain, and (iii) the presence of methyl substituents and bromine substituents on the hydroquinone and terephthalate groups, respectively, means that many isomeric structures are also possible. 

The samples used in the present study are (1) a copolymer consisting of p-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA) in the mole fraction ratios 73 27 and (2) a polymer which contains HBA, HNA, terephthalic acid (TA) and hydroquinone (HQ) in the ratios 57 41 1 1. It will be shown later that the incorporation of the small amount of TA and HQ into the latter structure makes the material less shear—thinning than the copolymer containing only HBA and HNA, when examined theologically. It is generally believed that a random sequence distribution of monomers occurs in both... 

For example, if a polyester contains two acids and two diols each in equal concentrations of 0.25 moles, its [MI]ab is calculated from L=2, ma=mb=0.25. If the two acid units are terephthalic acid and iso-phthalic acid then they score [MI]a= 6 and 4 respectively and if the diol units are hydroquinone and methyl hydroqui-none, then these score [MI]b=6 and 5 respectively Eq. (2) becomes... 

The calculation of the MI is still quite straightforward. Suppose a polymer comprises 75% of terephthalic acid/hydroquinone units (TPA/HQ) and 25% m-hydroxybenzoic acid (MHBA). As the corresponding MI scores for the units are 6 (TPA and HQ) and 4 (MHBA) the MI is calculated as follows ... 

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