Polyester prodn - from terephth alic acid and ethylene glycol, two step process using acid excess in first

摘要

Linear polyester prodn. by direct esterification of terephthalic acid (I) with ethylene glycol (II) in 1:1.1 to 1:1.5 mol. ratio at raised temp. and pressure up to partial pressure of (II) at temp. used, in presence of previously prepd. esterification product, followed by polycondensation, is modified by carrying out first step reaction under at least atmospheric pressure with (II):(I) mol. ratio 1:1, pref. at 1-5 atm. absolute and 240-260 degrees C and adding (II) bal. reqd. to achieve desired (I):(II) mol. ratio of 1:1.1 to 1:1.5 in the second step, under raised pressure, pref. at 240-280 degrees C, after completing the addn. of the required amt. of (I), and then completing esterification under pressure. Pure white polyesters of high m. pt. are produced. Esterification pref. takes place in presence of a catalyst, pref. Na terephthalate.