P-Hydroxybenzoic acid, terephthalic

Thermally stable copolymers of 3-(trimethylsiloxyl)- and 3,5-bis(trimethylsiloxyl)benzoyl chloride (4A) or 3-acetoxy- and 3,5-diace-toxy-benzoic acid (4B) were prepared with mole ratios of AB AB2 monomer ranging from 160-5.32 Polymers containing 10-20 mole % of branching monomers were insoluble in CHC13 but soluble in polar solvents, such as A,A-dimethylformamide (DMF) or a mixture of pyridine and benzene. Compared to the linear homopolymer of 3-hydroxy-benzoic acid, the branched polymer showed lower crystallinity and slower crystallization. There was an inverse linear relationship between percent crystallinity and the number of branches in the chain. Similarly, in an attempt to improve moldability and decrease anisotropy of rigid aromatic polyesters, 0.3-10 mole % of 1,3,5-trihydroxybenzene, 3,5-di-hydroxybenzoic acid, and 5-hydroxyisophthalic acid were copolymerized with p-hydroxybenzoic acid/terephthalic acid/4,4 -dihydroxy-diphenyl.33 The branched polymer showed a lower orientation and possessed improved flex properties. 

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

Grilen p-Hydroxybenzoic acid + terephthalic acid -1- glycol (fiber) Emser Werke, Switzerland... 

PC/LCP LCP derived from ethylene glycol-p-hydroxybenzoic acid-terephthalic acid/ C NMR/reaction kinetics showing which LCP segment was most active in transreaction Ho and Wei 1999 (see also Bum et al. 2001)... 

Figure 3 summarizes the molecular architecture used to promote polyester melt anisotropy at reasonable temperatures. The Celanese, DuPont and Eastman laboratories have outlined most of the key approaches to lower polymer melting point via crystalline order disruption. This is accomplished while maintaining sufficient molecular symmetry to preserve the melt anisotropy inherent in linear aromatic polyesters, that is, polyesters derived typically from symmetric monomers as p-hydroxybenzoic acid, terephthalic acid, hydroquinone, 4,4 -biphenol and the like. 

Much wider interest has been aroused by the development of copolymers of p-hydroxybenzoic acid which are commonly known as liquid crystal polymers. Polyesters of this type were introduced commercially in 1985 and details of their nature have not been fully disclosed. Two commercial products are currently available one is based on p-hydroxybenzoic acid and a hydroxynaphthoic acid whilst the other is based on p-hydroxybenzoic acid, terephthalic acid and p,p -dihydroxybiphenyl. 

Polymers based on these structures became available as Victrex SRP (ICI), Vectra (Hoechst) and Xydar (Amoco). It is reported that the Vectra materials are based on p-hydroxybenzoic acid and hydroxynaphthoic acid monomers, whilst Xydar is based on terephthalic acid, p-hydroxybenzoic acid and pp -dihydrox-ybiphenyl. Whilst properties vary between grades, in general they possess the following outstanding properties ... 

The effect of incorporating p-hydroxybenzoic acid (I) into the structures of various unsaturated polyesters synthesised from polyethylene terephthalate (PET) waste depolymerised by glycolysis at three different diethylene glycol (DEG) ratios with Mn acetate as transesterification catalyst, was studied. Copolyesters of PET modified using various I mole ratios showed excellent mechanical and chemical properties because of their liquid crystalline behaviour. The oligoesters obtained from the twelve modified unsaturated polyesters (MUP) were reacted with I and maleic anhydride, with variation of the I ratio with a view to determining the effect on mechanical... 

Compared with other polymeric materials. LCPs have very high unidirectional properties. Iei/nt7 1 (Celanese Corp.t resins are primarily aromatic polyesters based on p-hydroxybenzoic acid and hydroxynaphthoic acid monomers. Xytlar " (Celanese Carp.) injection molding resins are polyesters based on terephthalic acid. />. p -dihydruxybiphenyl and p-hydroxybenzoic acid Differences in monomers are primarily responsible for the differences in specific properties and end uses. The fibrous nature of the polymers imparls good impact strengths. 

In order to make polymers behave as liquid crystals it is necessary to introduce some structural rigidity. A typical polymer which has the required rigidity is poly(phenylenetetraphthalamide) (10.7). This material belongs to a class of polymer known as the aramids. Other liquid crystalline polymers are the thermotropic polyesters derived from p-hydroxybenzoic acid, py p -biphenol and terephthalic acid (10.8). 

Among the many different classes of thermotropic polymers, only a limited number of polyesters based on aromatic ester type mesogenic units have been studied by rheological methods, beginning with the publication by Jackson and Kuhfuss of their work on the p-oxybenzoate modified polyethylene terephthalate, PET, copolymers. They prepared a series of copolyesters of p-hydroxybenzoic acid, HBA, and PET and measured the apparent melt viscosity of the copolymers as a function of their composition by use of a capillary rheometer. On inclusion of low levels of HBA into PET, the melt viscosity increased because of partial replacement of the more... 

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). 

A whole series of high-performance polyester LCPs was introduced in 1985. They were assembled from p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid. Polyarylates (PARs) - amorphous phenolic esters derived from aromatic dicarboxylic acids (mixtures of terephthalic acid and isophthalic acid) and biphenols such as bisphenol A - are produced by Amoco (Ardel ), Celanese (Durel ) and DuPont (Arylon ) at a volume of approx. 2000 t/a. 

A polyester first prepared by Jackson (3) (20 mol% modified p-hydroxybenzoic acid poly(phenyl-1,4-phenylene terephthalate)) was spun at 320°C and fibers were characterized "as-made". The dynamic tensile modulus as a function of DR is seen in Figure 4 and shows that very high values are obtained at even low DR-values. 

Although studies concerning main chain liquid crystalline polymers were originated by Onsager (la) and Ishihara (lb) in the late 1940 s, extensive work in this field did not really begin until the early 1970 s. Jackson and Kuhfuss (2) reported the first thermotropic polyester by modifying polyethylene terephthalate with various amounts of p-hydroxybenzoic acid (HBA). They found that the copolyester with HBA content of at least 35 mole % have opaque melts. Subsequent studies in the area of aromatic polyesters by various authors resulted in a large number of patents and publication. (3.) These polymers were all derived from unsubstituted and... 

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... 

Copolyester of p-hydroxybenzoic acid with ethylene terephthalate (PHB-PET, 60/40) was supplied by Tennessee Eastman Kodak Co., whereas polyether imide (PEI) was provided by General Electric. Co. (Ultem 1000). These polymers were dissolved together in a mixed solvent of phenol and tetrachloroethane in the ratio of 60/40 by weight at 80°C for about a week. The polymer concentration of the solution was 2 wt7.. Various PHB-PET/PEI films were cast on glass slides at ambient temperature, then dried in a vacuum oven at 60°C for two weeks. Thicker films were prepared in Petri dishes for differential scanning calorimetric (DSC) studies. 

P8 M is not the only polymer forming the isotropic smectic phase. To date, we have observed formation of that phase for a half-dozen chiral polymethacrylates and polysiloxanes. Table 5.1 summarizes the chemical structure and phase behavior of synthesized side-chain homopolymers, which carry chirally substituted side chains derived from asymmetric esters of terephthalic acid and hydroquinone. Such a structure with alternating orientation of carboxylic link groups seems to favour the formation of the IsoSm phase, whereas isomeric derivatives of p-hydroxybenzoic acid, where all carboxylic links have the same orientation, form only conventional Sm A and Sm C phases. Molar mass of all the synthesized homo- and copoly(meth)acrylates is within the range of 1 to 2-10 g mol the poiysilox-anes have the average degree of polymerization, p 35. 

A high-performance, wholly aromatic copolyester suitble for injection molding was commercial introduced in late 1984 by Dartco Manufacturing under the trade name Xydar. Xydar injection-molding resins are based on terephthalic acid, p,p -dihydroxybiphenyl, and p-hydroxybenzoic acid. 

Among the first polymers observed to exhibit the aforesaid properties of LCPs were copolyesters (I) prepared from terephthalic acid, ethylene glycol, and p-hydroxybenzoic acid... 

FIGURE 5.5 Effect of p-hydroxybenzoic acid concentration on (a) melt viscosity and (b) tensile strength of a terephthalic acid/p-hydroxybenzoic acid/ethylene glycol copolyester. (After Lenze, R. W. and Lin, J. I. 1986. Polym. News, 11, 200.)... 

The first LCP to be launched commercially was Dartco s Xydar, introduced in 1984 [11]. Xydar injectionmolding resins are aromatic polyesters based on terephthalic acid, p-hydroxybenzoic acid, and p,p -dihydroxybiphenyl. Xydar has a high melting point (close to 400°C), which necessitates certain modifications to processing equipment. It also has a high melt viscosity making it difficult to mold in... 

Figure 3. Monomers and polymer structures of the unsubstituted para-linked aromatic polyesters, poly-(p-phenylene terephthalate) [poly(TA/HQ)] and poly-(p-hydroxybenzoic acid) [poly(HBA)].

Garozzo, D., Giuffrida, M., Montaudo, G., and Lenz, R.W., Mass Spectrometric Gharacterization of Random Ethylene terephthalate and p-Hydroxybenzoic Acid Copolyesters,. Polym. Sci. Polym. Chem. Ed, 25, 271 (1987). 

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