Patent ID: 7488852

Claim:
A process for the preparation of perfluoropolyethers having structural formula (I) R 1 O—(CF 2 O) n —(CF 2 CF 2 O) m R 2 (I) wherein: R 1 is —CH 3 or —C 2 H 5 ; R 2 is equal to R 1 or —CF 2 H; n is 0 or an integer from 1 to 100; m is an integer from 1 to 100; or when R 2 is —CF 2 H, then m can also be 0; and the oxyfluoroalkylene units —(CF 2 CF 2 O)— and —(CF 2 O)— are statistically distributed along the polymer chain, comprising the following steps: a) reaction between: a perfluoropolyether having —COF end groups of formula FOCCF 2 O—(CF 2 O) n —(CF 2 CF 2 O) m —CF 2 COF (II) wherein n, m are integers from 0 to 100, or a compound of formula FOC—COF (II bis); with an alkaline metal fluoride (M), in an aprotic polar solvent, at temperatures between 40° C. and 70° C., to yield the corresponding alcoholate having —CF 2 OM end groups; b) addition to the reaction compound obtained in step a) of an alkylating agent: an alkylsulphite of formula (R 1 O) 2 SO (III) wherein R 1 is —CH 3 or —C 2 H 5 , or a polymer having as repeating units perfluorooxyalkylene sulphonic esters, of formula (IV) T 1 O—(CF 2 CFO(CF 3 )) f —(CFO(CF 3 )) e —(CF 2 CF 2 O) d (CF 2 O) c —(CF 2 CFO(OCF 2 CF 2 SO 2 OR 1 ) b —(CFO) a -T 2 (IV) wherein R 1 has the above meaning; the coefficients a, b, c, d, e, f are integers, including zero, with at least a or b different from 0, so that their sum is such that the number average molecular weight be in the range 1,000-50,000; T 1 , T 2 equal to or different from each other, are selected from —CF 2 H, —CF 2 X, —C 3 F 7 , and wherein X is F, CF 3 , or Cl, keeping the reaction mixture under stirring, at a temperature in the range 110° C.-200° C., when the alkylsulphite (III) is used, and at temperatures in the range 0° C.-60° C., when perfluoropolyoxyalkylene sulphonic esters (IV) are used; c) the reaction mixture obtained in step b) is salified with a base, then it is distilled in steam flow obtaining an aqueous residue and a distillate from which an organic phase formed by the compound of formula (I) wherein R 1 and R 2 are methyl or ethyl, is separated; d) the distillation residue of step c) is acidified with a HCl solution, distilled under vacuum, in a range from 70° C. to 170° C., separating from the distillate an organic phase formed by a compound of formula (I) wherein R 1 is —CH 3 or —C 2 H 5 and R 2 is —CF 2 COOH, then salification with KOH or NaOH, subsequently decarboxylated by known methods obtaining the compound of formula (I) wherein R 1 is —CH 3 or —C 2 H 5 and R 2 is —CF 2 H.