DE2715932

The present invention is concerned with thermoplastic terephthalic acid copolyesters which crystallize more rapidly than homopolyethylene terephthalate and are based on a diol component which is about 98 to 99.9 mol % of ethylene glycol and the balance 2-ethylhexane-1,3-diol. The acid component may be up to about 10.0 mol % of other than terephthalic acid or its dimethyl ester. This invention is also concerned with a process of synthesizing such copolyesters by esterifying or transesterifying the acid and diol components between about 150 DEG and 250 DEG C. in the presence of appropriate catalysts. The condensation product may be subject to polycondensation at about 200 DEG to 300 DEG C. under reduced pressure in the presence of esterification catalysts. In a preferred embodiment the 2-ethylhexane-1,3-diol is added after the initial reaction between the acid component and the ethylene glycol and preferably after the degree of polycondensation is greater than 4.