Fluorine-substituted vicinal glycols of the formula ##STR1## in which the substituents R.sub.1 to R.sub.4, independently of one another, have the following meanings: R.sub.1 to R.sub.4 =H, fluorine, C.sub.1 - to C.sub.18 -alkyl in which some or all of the hydrogens may be substituted by fluorine, and at least one of the substituents R.sub.1 to R.sub.4 is a completely fluorinated alkyl or an alkyl of the formula--(CH.sub.2).sub.m --(C.sub.n F.sub.2n+1),in which m is 1 or 2, and n is an integer from 1 to 17, and x is 0 or 1.Furthermore, a method for the preparation of the fluorinated vicinal glycols is described. If the fluorinated vicinal glycols are condensed together with dicarboxylic acids, products having enhanced thermal stability are obtained.