Mono-methyl terephthalate

Fig. 1. Biodegradation of dimethyl terephthalate (DMT) by Pasteurella multocida Sa in the presence of ethanol. Ester hydrolysis of DMT involves a transesterification of mono-methyl terephthalate (MMT), and the formation of monoethyl terephthalate (MET).

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). 

When one methyl group has been oxidised, 4-toluic acid is formed. This intermediate is soluble in the solvent used, acetic acid. In the next step it is oxidised to terephthalic acid, which is almost insoluble in acetic acid. The intermediate product is 4-formylbenzoic acid. This cocrystallises with the final product. Since it is a mono-acid it will cause a termination of the polymerising chain. 

A selection of monosubstituted and disub-stituted poly-(/ -phenylene-terephthalate)s is compared in Table 2. Poly(p-phenylene-terephthalate)s with methyl, methoxy, chlo-ro, or bromo substituents on either the hy-droquinone or the terephthalic acid moiety exhibit melting temperatures of 350 °C or higher. Thermotropic liquid crystalline behavior is observed in these samples, although it is in the range of thermal decomposition. A comparison of the mono- and diphenyl substituted polyesters reveals an important trend. The monosubstituted poly-(p-phenylene-terephthalate) with the phenyl substituent in the hydroquinone moiety melts at 346 °C, also forming a nematic melt up to a clearing temperature of... 

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