Peroxide curable fluoropolymers obtainable by polymerization with non-fluorinated emulsifiers

A curable fluoropolymer containing repeating units derived from vinylidene fluoride (VDF) and tetrafluoroethylene (TFE) and at least one other fluorinated comonomer and further containing (i) —CF2CH2I end groups and (ii) branching sites derived from one or more perfluorinated bisolefinic ether modifier;

• wherein the polymer is obtained by an aqueous emulsion polymerization comprising the addition of one or more non-fluorinated emulsifier but wherein essentially no fluorinated emulsifier is added;
• and
• wherein the one or more perfluorinated bisolefinic ether modifier correspond to the general formula:
• CF2═CF—(CF2)n—O—(Rf)—O—(CF2)m—CF═CF2
• wherein n and m are independent from each other either 1 or 0 and wherein Rf represents a perfluorinated linear or branched, cyclic or acyclic aliphatic or aromatic hydrocarbon residue that may be interrupted by one or more oxygen atoms and comprises up to 30 carbon atoms, the curable fluoropolymer further having units derived from a cure site monomer selected from the general formula:
• Rf—CF(I)—(CX2)n—(CX2CXR)m—O—R″f—Ok—(CXR′CX2)p—(CX2)q—CF(I)—R′f
• wherein X is independently selected from F, H, and Cl;
• Rf and R′f are independently selected from F and a monovalent perfluoroalkane having 1-3 carbons;
• R is F, or a partially fluorinated or perfluorinated alkane comprising 1-3 carbons;
• R″f is a divalent fluoroalkylene having 1-5 carbons or a divalent fluorinated alkylene ether having 1-8 carbons and at least one ether linkage;
• k is 0 or 1;
• and n, m, and p are independently selected from an integer from 0-5, wherein, n plus m is at least 1 and p plus q is at least 1.

Method of making a curable fluoropolymer comprising

• i) providing a seed composition obtained by aqueous emulsion polymerization of one fluorinated monomer and at least one other fluorinated comonomer essentially in the absence of a fluorinated emulsifier but in the presence of one or more non-fluorinated saturated emulsifier;
• ii) polymerizing VDF, TFE and at least one other comonomer in an aqueous emulsion polymerization the presence of the seed composition and in the absence of any added fluorinated emulsifiers but in the presence of an iodine-containing chain transfer agent (CTA), one or more perfluorinated bisolefinic ether modifier(s) and, optionally, one or more iodine-containing cures site monomers, wherein the iodine-containing CTA is selected from fluorinated iodo-olefins wherein the olefin chain may be interrupted once or more than once by an ether oxygen, and wherein the modifier is selected from perfluorinated bisolefinic ether modifiers corresponding to the general formula:
• CF2═CF—(CF2)n—O—(Rf)—O—(CF2)m—CF═CF2
• wherein n and m are independent from each other either 1 or 0 and wherein Rf represents a perfluorinated linear or branched, cyclic or acyclic aliphatic or aromatic hydrocarbon residue that may be interrupted by one or more oxygen atoms and comprises up to 30 carbon atoms;
• wherein the curable fluoropolymer contains (i) —CF2CH2I end groups and (ii) branching sites derived from the one or more perfluorinated bisolefinic ether modifier(s).