1) Disclosed herein are new fluorine-containing compounds having polyacetalic structure, of general formula:[Rf.sub.m --CH.sub.2 O(CH.sub.2 O).sub.c --CH.sub.2 --.brket close-st..sub.n (I)where:Rf=a perfluorooxyalkylene chain having Mn from 500 to 5,000;m=4-25;c=1-10;n=2-100.2) A process for preparing them which comprises carrying out the polycondensation of diols having formula:HORfOH (II)with formaldehyde, in mass or in the presence of solvents, in an acid medium. The compounds of formula (I) can be oligomeric compounds (polymerization degree x.sub.n from 2 to about 20) or polymeric compounds (x.sub.n from about 20 to about 100). They exhibit a high stability to heat and to chemical agents, and Tg values slightly different from the ones of the diols utilized for preparing them.