Ethylene glycol dicarboxylic acid, polyesters

Polymerisation of a diol with a dicarboxylic acid is exemplified by the production of a polyester from ethylene glycol and terephthalic acid either by direct esterification or by a catalysed ester-interchange reaction. The resulting polyester Terylene) is used for the manufacture of fibres and fabrics, and has high tensile strength and resiliency its structure is probably ... 

Prior to polymerization, p-xylene is first oxidized to terephthalic acid (TA) or dimethyl terephtalate (DMT). These diacid or dimethyl ester monomers are then polymerized via a condensation reaction with ethylene glycol to form the polyester. Prior to the development of a method to purify TA to make purified terephtahc acid (PTA, >99% pure) by the Mid-Century Corporation in the 1950s [10], DMT was the primary way to obtain the purified dicarboxylate. The Amoco Oil Company, now part of BP International, made several improvements to the PTA process since its inception [11]. Since the advent of the availability of PTA, it has become the monomer of choice over DMT. PTA avoids the complications of including methanol to enable purification and handling the methanol evolved during the polymerization to polyester. 

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). 

In equation 1, a dicarboxylic acid derivative called an anhydride (literally without water ) reacts with ethylene glycol, a di-alcohol, to form a linear polyester and the byproduct water. Ethylene glycol is the major ingredient in most automotive radiator fluids. In equation 2, the ethylene glycol is replaced with a tri-alcohol, glycerol. As the reaction proceeds, the polyester does not form linear chains, but rather becomes crosslinked as the three OH groups react with phthalic anhydride, building up a three-dimensional structure. 

Table IV. Polyesters of Ethylene Glycol and Dicarboxylic Acids...

Transesterification (also known as ester exchange, ester interchange, or ester alcoholysis) is the most important of the esterification reactions. Polyesters of relatively low molecular weight (around 2000) prepared from aliphatic dicarboxylic acids and glycols are most commonly made by direct esterification (Section 5.2) with or without addition of an external acidic catalyst. Phosphoric acid, p-toluenesulphonic acid, and antimony pentafluoride have been used as catalysts. The preparation of PET by the direct esterification of TA with ethylene glycol was not practical until the... 

Polyesters (short for po/ymeric esters ) are condensation polymers that are formed when dihydric alcohols react with dicarboxylic acids. An ester linkage is formed at each end of each monomer molecule to build up large molecules. A useful polyester is prepared from terephthalic acid and ethylene glycol. 

Poly(ethylene glycol) is used to plasticize proteins, casein, gelatin, and poly(vinyl alcohol). Polyester plasticizers are condensation products of dicarboxylic acid with simple alcohols corresponding to the following two general formulas ... 

A transesterification reaction is used to make the polyester fibres that are used for textile production. Terylene, or Dacron, for example, is a polyester of the dicarboxylic acid terephthallc acid and the did ethylene glycol. 

The usual synthetic route to a polyester is by condensation of a dicarboxylic acid with a diol. The best known polyester is poly(ethylene terephthalate) prepared from ethylene glycol and terephthalic acid. 

The saturated polyesters that find conunercial applications are mostly linear, except for some specially prepared branched polymers used in the preparation of polyurethanes. The linear polyesters became commercially important materials early in this century and still find many uses in industry. The earliest studies reported condensations of ethylene, trimethylene, hexamethylene, and de-camethylene glycols with malonic, succinic, adipic, sebacic, and orthophthalic acids. Later studies showed that such condensations yield high molecular weight compounds. Nevertheless, these polyesters exhibit poor hydrolytic stability and are generally low-melting. Subsequently, however, it was found that aromatic dicarboxylic acids yield polymers with high melting points, and poly(ethylene terephthalate), which melts at 265 C, is now an important commercial material. 

The first polyester, developed in the 1940s, involved the polymerization of benzene 1,4-dicarboxylic acid (terephthalic acid) with 1,2-ethanediol (ethylene glycol) to give poly-(ethylene terephthalate), abbreviated PET. Virtually aU PET is now made from the dimethyl ester of terephthahc acid by the following transesterification reaction (Section 14.4C) ... 

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