Process for manufacturing a dispersion of a vinylidene fluoride polymer

A process for manufacturing a dispersion of a vinylidene fluoride (VDF) thermoplastic polymer (polymer (F)), said process comprising polymerizing VDF in an aqueous phase comprising:

• at least one surfactant selected from the group consisting of non-fluorinated surfactants (surfactant (HS)) and fluorinated surfactants having a molecular weight of less than 400 (surfactant (FS)) selected from the group consisting of:
• surfactant (FS) complying with formula (IA) here below:
• Rf—(OCF2CF2)k−1—O—CF2—COOXa (IA)
• wherein Rf is a C1-C3 perfluoroalkyl group comprising, optionally, one or more ether oxygen atoms, k is 2 or 3 and Xa is selected from a monovalent metal and an ammonium group of formula NRN4, wherein RN, equal or different at each occurrence, is a hydrogen atom or a C1-C3 alkyl group;
• and
• surfactant (FS) complying with formula:
• RFS-E-Yr
• wherein:
• Yr is an anionic functionality;
• wherein E is a C4-C24 hydrocarbon non fluorinated divalent group, possibly comprising one or more catenary oxygen atom(s);
• and
• wherein RFS is a —ORFSf group, a N(RFSf)2, or a —OAr(RFSf)r group, wherein RFSf, equal to or different from each other at each occurrence, is a C1-C6 perfluoroalkyl group, Ar is an aromatic moiety (e.g. a phenyl group), and r is an integer of 1 to 3;
• and
• at least one functional (per)fluoropolyether (functional PFPE) comprising at least one (per)fluoropolyoxyalkylene chain [chain (R′F)] and at least one functional group, said functional PFPE having a number average molecular weight of at least 1000 and a solubility in water of less than 1% by weight at 25° C.,
• wherein said functional PFPE is present in the aqueous phase in an amount of 0.001 to 0.005 g/l,
• wherein at least 60 mol. % of the recurring units constituting polymer F are derived from VDF,
• wherein the dispersion has an average particle size of 250 to 300 nm;
• and
• wherein the at least one functional PFPE complies with formula (XIV) here below:
• XpOOC—CF2—O—(CF2)n′(CF2CF2O)m′—CF2—COOXp (XIV),
• wherein n′ and m′ are independently integers>0 such that the number average molecular weight of the functional PFPE is at least 1000, the recurring units being generally statistically distributed along the perfluoropolyoxyalkylene chain, and Xp, equal to or different from each other, is a hydrogen atom, a monovalent metal, or an ammonium group of formula —N(R′n)4, wherein R′n, equal or different at each occurrence, is a hydrogen atom or a C1-C6 hydrocarbon group.