Continuous prodn of a polyalkylene tere - phthalate

TLDR: In this article, a mixture of bis-(hydroxyalkylene)-terephthalate and oligomers thereof is used to obtain a precondensate, which is then polycondensed and re-esterified in a second reaction zone, with the aid of added glycol.

Abstract: Terephthalic acid is polycondensed, in a first reaction zone, with a mixture of bis-(hydroxyalkylene)-terephthalate and oligomers thereof so as to obtain a precondensate; a part of the precondensate obtained is then polycondensed in known manner; and the remainder of the precondensate is then re-esterified, in a second reaction zone, with the aid of added glycol so as to obtain bis-(hydroxyalkylene)-terephthalate and oligomers thereof; and the mixture obtained is finally recycled to the first reaction zone. This method avoids known disadvantages of direct reaction of terephthalic acid with glycol or transesterification of a terephthalate.