Terephthalic acid, reaction with ethylene glycol

In the TA process, ethylene glycol and purified terephthalate acid are generally mixed in a ratio of less than 1.4 to 1 and heated in an initial phase with an antimony oxide catalyst to the boiling point of the ethylene glycol (198 °C). Because the reaction is relatively slow at this temperature, this step is often run under pressure to increase the achievable temperatures. As the reaction proceeds and the BHET is produced, the temperatures are Increased and the pressure is lowered to allow distillation of the evolved ethylene glycol. This phase resembles the PC step of the El process. 

Condensation polymerization differs from addition polymerization in that the polymer is formed by reaction of monomers, each step in the process resulting in the elimination of some easily removed molecule (often water). E.g. the polyester polyethylene terephthalate (Terylene) is formed by the condensation polymerization (polycondensation) of ethylene glycol with terephthalic acid ... 

The largest commercial use of ethylene glycol is its reaction with dicarboxyUc acids to form linear polyesters. Poly(ethylene terephthalate)... 

An alternative route to PET is by the direct reaction of terephthalic acid and ethylene oxide. The product bis(2-hydroxyethyl)terephthalate reacts in a second step with TPA to form a dimer and ethylene glycol, which is released under reduced pressure at approximately 300°C. 

This new monomer is separated from the excess glycol and polymerized. The monomer has two hydroxy endgroups but with catalysis and temperature, it will self-condense to give ethylene glycol as the by-product. The overall result is a one-to-one reaction of terephthalic acid with ethylene glycol, but a substantial amount of glycol is internally recycled. 

PET is a polycondensation polymer based on the reaction of terephthalic acid (TA) and mono-ethylene glycol (MEG) or alternatively with di-methyl terephtha-late (DMT) plus MEG (Figure 10). 

FIGURE 4.5 Plot of average chain length DP, as a function of reaction time for the acid-catalyzed condensation of ethylene glycol with terephthalic acid producing poly(ethylene terephthalate) (PET). 

The largest commercial use of ethylene glycol is its reaction with dicarboxylic acids to form linear polyesters. Polyethylene terephthalate) [25038-59-9] (PET) is produced by esterification of terephthalic acid [100-21 -0] (1) to form bishydroxyethyl terephthalate [959-26-2] (BHET) (2). BHET polymerizes in a transesterification reaction catalyzed by antimony oxide to form PET (3). 

Just as diacids and diamines react to give polyamides, diacids and dialcohols react to give polyesters. The most industrially important polyester, made from reaction of terephthalic acid (1,4-benzenedicarboxylic acid) with ethylene glycol (1,2-ethanediol), is used under the trade name Dacron to make clothing fiber and under the name Mylar to make plastic film and recording tape. 

One important group of condensation polymers is the polyesters. The most important commercial polyester is formed from the reaction of terephthalic acid (a diacid) with ethylene glycol (a diol). This polymerization occurs in a stepwise fashion (hence the name step growth polymerization). First, one carboxylic acid group of a diacid molecule and one hydroxy group of a diol molecule combine to form an ester, with the loss of water. Then a second diol molecule reacts with the unreacted caiboxylic group on the other end of the diacid molecule, or a second diacid molecule reacts with the unreacted hydroxy group of the diol. Continuation of this process adds a new monomer unit at... 

Figure 6. Esterification of terephthalic acid with ethylene glycol reaction temperature 473 K, reaction time 90 min.

Phthalocyanines with M = Si(OH)2 or Ge(OH)2 were eovalently incorporated into polyesters during the polycondensation of terephthalic acid dimethylester and ethylene glycol [182]. With only lO" molar amounts of dye, the polyesters are intensely blue-colored. Good solubility can be achieved in water by axial substitution at the central metal or with hydrophilic polymers. Phthalocyanines with the tetravalent M = SiCb were reacted with the sodium salt of methoxypoly(oxyethylene) (M = 5000 Da) to give the blue-colored polymer 68 which is soluble in water and some organic solvents [183]. The reaction of phthalocyanines with the trivalent M = AlCl with poly-(oxyethylene) or poly(vinylalcohol) also led to water-soluble polymers having covalent bonds of the polymers at the Al(III) [184]. These water-soluble materials have been tested in the photodynamic therapy of cancer. 

An alternative to the foregoing process, which uses only physical methods of purification, is chemical recycling. Large amounts of PET film scrap are salvaged by a transesterification reaction. The scrap is treated with methanol in the presence of an acid catalyst to give ethylene glycol and dimethyl terephthalate, monomers that are purified by distillation or recrystallization and used as feedstocks for the production of more... 

Currently, about 30% of PET soft-drink bottles are being recycled. In one recycling process, scrap PET is heated with methanol in the presence of an acid catalyst. The methanol reacts with the polymer, liberating ethylene glycol and dimethyl terephthalate. These monomers are then used as feedstock for the production of new PET products. Write an equation for the reaction of PET with methanol to give ethylene glycol and dimethyl terephthalate. 

Thus, the reaction of ethylene glycol (a diol) with two equivalents of benzoic acid (a mono carboxylic acid) or the reaction of terephthalic acid (a dicarboxylic acid) with ethanol (a mono hydroxy compound) lead to the... 

In practice, one of the ways poly(ethylene terephthalate) is prepared is as follows. First a diester is formed as a result of the reaction of terephthalic acid with ethylene glycol. This is heated at about 270 C resulting in the loss of ethylene glyol to afford high-molecular-weight poly(ethylene terephthalate) (PET) (see Eq. 2.57). 

Polyesters contain carboxylic ester linkages (-0-C0-) in the backbone. Polyesters are synthesized by reaction of a diol and a dicarbonic acid, e.g. poly(ethylene terephthalate) (PET) by polycondenastion of ethylene glycol and dimethyl terephthalate. Poly(butylene terephthalate) (PBT) is produced by reaction with butylene glycol. Structures of PET and PBT are shown in Fig. 2.2.7. 

Polyfethylene terephthalate) 2GT.— The formation of 2GT from the direct interaction of terephthalic acid with ethylene glycol rather than the transesterification process formerly used, has been the subject of several papers. These have dealt with the production of high purity terephthalic acid, the rheological aspects of its processing and analysis of reaction mixtures by gel permeation chromatography. The formation of 2GT and characterization of the derived fibres from the direct interaction of ethylene oxide with terephthalic acid has also been described. ... 

Poly(ethylene terephthalate) (abbreviated PET or PETE) is a semi-aromatic thermoplastic polyester obtained by condensation reaction of difunctional reactants and well-known for more than 60 years. PET is commonly produced by esterification reaction between terephthalic acid and ethylene glycol with water as a byproduct or by transesterification reaction between ethylene glycol and dimethyl terephthalate with methanol as a byproduct. In order to obtain high molar masses polymers, solid-state polymerization is carried out. PET is one of the most important industrial polymers because of its excellent properties as tensile impact strength, chemical resistance, processability, clarity, thermal stability and others. The main applications of PET are fibers for textiles, films and bottles. Annual world PET production is around 60 millions tons. PET materials were manufactured using extrusion, injection molding and blow molding techniques. 

The principal solvolytic reactions for PET are hydrolysis with reaction products terephthalic acid and ethylene glycol, methanolysis with reaction products dimethyl terephthalate and ethylene glycol, and glycolysis with reaction products a mixture of polyols. 

Resins with long-chain macromolecules obtained by polycondensation have thermoplastic properties. Polyesters ( Terylene ) and polyamides (Nylon) are examples of polycondensations. The synthetic fibre Terylene (known as Dacron in the USA) is a polyester formed by the reaction of ethylene glycol with terephthalic acid the latter is obtained from p-xylene by oxidation ... 

These reactions are the basis for the commercial preparation of polyesters. Polyesters are formed from a dicarboxylic acid and a dialcohol. The largest volume polyester is polyethylene terephthalate (PET). Rynite (Dupont) is a common brand. This is a condensation polymer and made by the removal of water in the condensation reaction of ethylene glycol with terephthalic acid. Note that all of the atoms of the monomers are not present in the hnal polymer. This is different from addition polymers. 

PolyCethylene terephthalate) is produced by polycondensation of bis(hydroxy-ethyl)terephthalate (BHET) or its oligomers. BHET may be synthesized both by the reaction of dimethyl terephthalte (DMT) and ethylene glycol (EG) and by the direct esterification of EG with terephthalic acid. Although direct esterification has recently gained importance, the DMT method remains the main process for obtaining BHET. This latter process provides the formation of DMT solution in EG, the transesterification of DMT with EG and distillation of methanol with formation of BHET, and finally, BHET polycondensation. The DMT EG molar ratio is 1 2 with an excess of EG (0.2 to 0.5 mol). Preheating of EG to 120 to 160°C and introduction of DMT in the molten state shortens the DMT dissolving time. 

Polyethylene terephthalate, commonly referred as polyester, can be made by several slightly differing routes. In the terephthalic acid process, ethylene glycol is reacted with terephthalic acid at temperatures above 200 °C, which drives the reaction forward by removal of water. An alternative process utilizes ester exchange to reach high molecular weights. 

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