Patent ID: 7214833

Claim:
A process to obtain perfluoropolyethers having a reduced absorption at wave lengths lower than 250 nm and having the formula: X 1 —O(CF 2 O) n (CF 2 CF 2 O) m (CF 2 CF 2 CF 2 O) p (CF 2 CF 2 CF 2 CF 2 O) q —X 2 (I) wherein: the repeating units —CF 2 O—, —CF 2 CF 2 O—, —CF 2 CF 2 CF 2 O—, —CF 2 CF 2 CF 2 CF 2 O— are statistically distributed along the chain; —X 1 and —X 2 are perfluoroalkyl chain end groups equal to or different from each other, having formula —(CF 2 ) z CF 3 wherein z is an integer from 0 to 3; n, m, p, q are integers comprised between 0 and 100, with the proviso that: at least one among n, m, p and q is different from zero; the ratio between the oxygen atoms and the carbon atoms O/C is higher than 0.33; wherein the chlorine atoms, determined by 19 F-NMR, are absent, wherein said process comprises the following steps: a) synthesis of the peroxidic perfluoropolyether, carried out by one of the following reactions: a1) TFE photooxidation in the presence of UV light, at low temperature, generally from −40° C. to 100° C., in liquid solvents under the reaction conditions selected between perfluorocarbons and (mono)hydrofluorocarbons, represented by the following general formula: C y F (2y+2−x) H x (II) wherein y is an integer from 2 to 4; x is an integer equal to 0 or 1; in the presence of fluorine, as regulating agent of the molecular weight, diluted with an inert gas; or a2) TFE oxidation using as radical initiator fluorine or hypofluorites of formula R f OF (III) R f being a pefluoroalkyl radical from 1 to 3 carbon atoms, by operating in the temperature range from −400° C. to −100° C. at a pressure between 0 and 12 bar, in an inert solvent under the reaction conditions, also containing chlorine; b) thermal treatment of the peroxidic product obtained in step a) at a temperature from 150° C. to 250° C., optionally in the presence of a molecular weight regulator selected between fluorine or hypofluorite of formula (III); c) treatment with fluorine of the polymer obtained in step b) at temperatures from 100° C. to 250° C., or by treatment with fluorine in the presence of UV radiations, operating at temperatures from −50° C. to 120° C.