Patent ID: 7288682

Claim:
A process for separating bifunctional perfluoropolyethers having two methylol terminations —CH 2 OH from their mixtures with monofunctional perfluoropolyethers with one methylol termination —CH 2 OH, optionally containing perfluoropolyethers with non functionalized end groups, having general formula X 1 —O—Rf—Y (I) wherein: Rf is a perfluoropolyoxyalkylene chain having a number average molecular weight of 500-10,000 comprising units of (C 2 F 4 O), (CF 2 O), (C 3 F 6 O) type, the unit (C 3 F 6 O) can represent units of formula —(CF 2 CF(CF 3 )O) or —(CF(CF 3 )CF 2 O); —(CF 2 (CF 2 ) z CF 2 O) wherein z is an integer equal to 1 or 2; —CR 4 R 5 CF 2 CF 2 O— wherein R 4 and R 5 are equal to or different from each other and selected from H, Cl or perfluoroalkyl, said units being statistically distributed along the chain; X 1 and Y are end groups selected from —CFXCH 2 OH (wherein X is F or CF 3 ), —CF 3 , —CF 2 Cl, —CF 2 CF 2 Cl, —C 3 F 6 Cl, —CF 2 Br, —CF 2 CF 3 , wherein at least one of the two end groups is —CFXCH 2 OH, comprising the following steps: a) addition of the perfluoropolyether mixture to an adsorbing solid phase, optionally dispersed in an apolar solvent, contained in a reactor equipped with stirring, with a mixture/solid phase ratio from 0.1 to 10 w/w, leaving under stirring for a time between 15 minutes and 6 hours at a temperature between 10° and 150° C.; b) filtration of the mixture obtained from step a), with separation of a solid phase containing adsorbed perfluoropolyether mixture enriched in bifunctional perfluoropolyethers and a liquid containing a perfluoropolyether mixture having diminished bifunctional species; c) addition to the solid phase obtained in b), of a perfluoropolyether mixture having an average functionality higher than that of the perfluoropolyether mixture of the liquid obtained in b), in a mixture/solid phase ratio between 0.1 and 2 w/w, optionally together with an apolar solvent, leaving under stirring for a time between 15 minutes and 6 hours, at a temperature between 10° and 150° C.; c1) optional repetitions of the operations of steps b) and c), until reaching the desired high functionality of the adsorbed perfluoropolyether; c2) filtration to separate the adsorbing solid phase from the liquid; d) addition to the solid phase separated in c2) containing adsorbed the perfluoropolyether having the desired high functionality, of a polar solvent in an amount of 1-10 w/w, stirring at 5°-150° C.; e) filtration of the mixture resulting from step d) with separation of a liquid containing the perfluoropolyether having the desired high functionality which is then isolated from the solvent.