Process for the manufacture of polyether polymers

A method for manufacturing a mixture of polymers [mixture (PFFCOOH—CF3)], said mixture (PFFCOOH—CF3) comprising polymers possessing a backbone consisting of a sequence of recurring units of formula —O—CF2—RF—CF2—O—CF2CF2—(CRf1Rf2)a—O—Rf—O—(CRf1Rf2)b—CF2CF2—,

• wherein:
• Rf is a C1-C18 perfluorocarbon group, possibly comprising one or more than one ethereal oxygen;
• RF is a bond or a C1-C18 perfluorocarbon group, possibly comprising one or more than one ethereal oxygen;
• each of Rf1 and Rf2, equal to or different from each other, is F or a C1-C6 perfluorocarbon group;
• a and b being independently zero or 1 and being collectively zero or 1;
• and said polymers having chain ends selected from the group consisting of —COOH and —CXF1XF2F, with XF1 and XF2 being F or a C1-C3 perfluoroalkyl group;
• said process comprising:
• Step (1):
• a step of reacting:
• (1a) at least one perfluoro compound [compound (F)] of formula CF2═CF—(CRf1 Rf2) a —O—Rf—O—(CRf1Rf2)b—CF═CF2,
• wherein Rf, Rf1, Rf2, a and b have the meaning defined above;
• and
• (1b) at least one hydrogen-containing compound [compound (H)] of formula:
• HO—CH2—RH—CH2—OH,
• with RH being a bond or a C1-C18 (fluoro)hydrocarbon group, optionally comprising one or more than one ethereal oxygen,
• in molar ratio compound (H):compound (F) of exceeding 1:1, so as to generate a mixture (PFHOH—OH) comprising a major amount of any di-hydroxy compounds of formula (I):
• HO—CH2—RH—[CH2—O—CF2CHF—(CRf1Rf2)a—O—Rf—O—(CRf1Rf2)b—CFHCF2—O—CH2—RH—]n—CH2—OH;
• and optionally comprising a minor amount of any compounds of formula (II):
• wherein in formulae (I) and (II) RH, Rf, Rf1, Rf2, a and b have the meaning defined above, and n is such that the number averaged molecular weight of compounds (I) is of 300 to 50 000;
• Step (2):
• a step of reacting mixture (PFHOH—OH) with COF2, so as to generate a mixture (PFHOC(O)F—OC(O)F) comprising a major amount of any di-fluoroformate compounds of formula (III):
• F—C(O)—O—CH2—RH—[CH2—O—CF2CHF—(CRf1Rf2)a—O—Rf—O—(CRf1Rf2)b—CFHCF2—O—CH2—RH—]n′—CH2—O—C(O)—F;
• and optionally comprising a minor amount of a compound of formula (II), as above detailed, wherein, in formula (III), RH, Rf, Rf1, Rf2, a and b have the meaning defined above, and n′ is such that the number averaged molecular weight of compounds (I) is of 300 to 50 000;
• Step (3):
• a step of fluorinating mixture (PFHOC(O)F—OC(O)F) with a source of molecular fluorine, so as to generate a mixture (PFFOC(O)F—OC(O)F) comprising a major amount of a perfluorinated di-fluoroformate compound of formula (IV):
• F—C(O)—O—CF2—RF—[—CF2—O—CF2CF2—(CRf1Rf2)a—O—Rf—O—(CRf1Rf2)b—CF2CF2—O—CF2—RF—]n″—CF2O—C(O)—F, and optionally comprising a minor amount of a compound of formula (V):
• wherein in formulae (IV) and (V) RF, Rf, Rf1, Rf2, a and b have the meaning defined above;
• and n″ is such that the number averaged molecular weight of compounds (I) is of 300 to 50 000;
• Step (4):
• a step of hydrolysing mixture (PFFOC(O)F—OC(O)F) in the presence of water, so as to generate a mixture (PFFCOOH—COOH) comprising a major amount of a perfluorinated di-carboxylic acid compound of formula (VII):
• HOOC—RF—[—CF2—O—CF2CF2—(CRf1Rf2)a—O—Rf—O—(CRf1Rf2)b—CF2CF2—O—CF2—RF]n′″—COOH, and optionally comprising a minor amount of a compound of formula (V), as detailed above, wherein in formula (VII) RF, Rf, Rf1, Rf2, a and b have the meaning defined above, and n′″ is such that the number averaged molecular weight of compounds (I) is of 300 to 50 000;
• Step (5):
• a step of fluorinating mixture (PFFCOOH—COOH), by contacting with a source of molecular fluorine, wherein the required amount of fluorine to convert the targeted fraction of —COOH end groups to generate the mixture (PFFCOOH—COOH), as detailed above, is added.