The copolymer includes divalent units represented by formula —[CF.sub.2—CF.sub.2]—, divalent units represented by formula; and one or more divalent units independently represented by formula: The copolymer has an —SO.sub.2X equivalent weight in a range from 300 to 2000. A polymer electrolyte membrane that includes the copolymer and a membrane electrode assembly that includes such a polymer electrolyte membrane are also provided.

A water repellent composition comprising a fluorinated copolymer having structural units based on a monomer (a) having a C.sub.1-6 polyfluoroalkyl group, structural units based on a monomer (b) having a C.sub.1-6 alkyl group and structural units based on a monomer (c) (halogenated olefin), and a medium, wherein the proportion of the structural units based on the monomer (a) is from 50 to 90 mass % of the structural units (100 mass %) based on all the monomers.

A water repellent composition comprising a fluorinated copolymer having structural units based on a monomer (a) having a C.sub.1-6 polyfluoroalkyl group, structural units based on a monomer (b) having a C.sub.1-6 alkyl group and structural units based on a monomer (c) (halogenated olefin), and a medium, wherein the proportion of the structural units based on the monomer (a) is from 50 to 90 mass % of the structural units (100 mass %) based on all the monomers.

A process for the preparation of a fluoroolefin polymer from an azeotropic mixture of monomers having a constant composition, the process including the step of:

contacting in a reaction zone:

(i) an initiator; and

(ii) an azeotropic mixture of monomers including at least one fluoroolefin and, optionally, at least one ethylenically unsaturated comonomer capable of copolymerizing therewith;

wherein the contacting is carried out at a temperature, pressure and

length of time sufficient to produce the fluoroolefin polymer.

A process for the preparation of a fluoroolefin polymer from an azeotropic mixture of monomers having a constant composition, the process including the step of:

contacting in a reaction zone:

(i) an initiator; and

(ii) an azeotropic mixture of monomers including at least one fluoroolefin and, optionally, at least one ethylenically unsaturated comonomer capable of copolymerizing therewith;

wherein the contacting is carried out at a temperature, pressure and

length of time sufficient to produce the fluoroolefin polymer.

A process for the preparation of a fluoroolefin polymer from an azeotropic mixture of monomers having a constant composition, the process including the step of:

contacting in a reaction zone:

(i) an initiator; and

(ii) an azeotropic mixture of monomers including at least one fluoroolefin and, optionally, at least one ethylenically unsaturated comonomer capable of copolymerizing therewith;

wherein the contacting is carried out at a temperature, pressure and

length of time sufficient to produce the fluoroolefin polymer.

An object of the present invention is to provide a redox flow secondary battery being low in the electric resistance and excellent in the current efficiency as well, and further having the durability. The present invention relates to an electrolyte membrane for a redox flow secondary battery, the electrolyte membrane containing an ion-exchange resin composition containing a fluorine-based polyelectrolyte polymer, and having an ion cluster diameter of 1.00 to 2.95 nm as measured in water at 25° C. by a small angle X-ray method, and to a redox flow secondary battery using the electrolyte membrane.

An object of the present invention is to provide a redox flow secondary battery being low in the electric resistance and excellent in the current efficiency as well, and further having the durability. The present invention relates to an electrolyte membrane for a redox flow secondary battery, the electrolyte membrane containing an ion-exchange resin composition containing a fluorine-based polyelectrolyte polymer, and having an ion cluster diameter of 1.00 to 2.95 nm as measured in water at 25° C. by a small angle X-ray method, and to a redox flow secondary battery using the electrolyte membrane.

The invention relates to a method for preparation of a polymer from monomers comprising polyvinylidene fluoride, trifluoroethylene and a third monomer, the method successively comprising: injection of all the monomers to react into a reactor; initiation of a polymerization of the monomers; a continuation step (a) of the polymerization of the monomers, during which a drop in pressure in the reactor is compensated.

A compound having a group represented by the formula (Ia): ##STR00001##
wherein R.sup.1 represents a C.sub.1 to C.sub.8 fluorinated alkyl group, R.sup.2 represents a group having an optionally substituted C.sub.5 to C.sub.18 alicyclic hydrocarbon group, and * represents a binding site.