The present invention relates to a process for preparing a fluoropolymer in a liquid reaction medium, comprising the following steps: provide a reactor containing a liquid reaction medium comprising water introduce in said reactor ethylene monomers and fluorinated monomers, said fluorinated monomers being selected from tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE) or mixtures thereof, pressurize the reactor, initiate polymerization feeding into said reactor a redox initiator comprising an oxidising agent and a reducing agent, wherein said reducing agent in said redox couple initiator is free from sulphur atoms having an oxidation number of 4 or below, wherein the reaction medium is free of fluorinated surfactants.

To provide a powder dispersion comprising a tetrafluoroethylene polymer, a particular polyoxyalkylene-modified polydimethylsiloxane and a liquid dispersion medium, and a composite having a baked product having physical properties intrinsic to the tetrafluoroethylene polymer. [Solution] The powder dispersion of the present invention comprises a powder of a tetrafluorethylene polymer, a liquid dispersion medium and a polyoxyalkylene-modified polydimethylsiloxane having a weight average molecular weight of at most 3,000 and an HLB value of from 1 to 18 calculated by Griffin's equation The composite of the present invention is produced by applying the powder dispersion of the present invention to the surface of a substrate and heating the powder dispersion.

To provide a powder dispersion comprising a tetrafluoroethylene polymer, a particular polyoxyalkylene-modified polydimethylsiloxane and a liquid dispersion medium, and a composite having a baked product having physical properties intrinsic to the tetrafluoroethylene polymer. [Solution] The powder dispersion of the present invention comprises a powder of a tetrafluorethylene polymer, a liquid dispersion medium and a polyoxyalkylene-modified polydimethylsiloxane having a weight average molecular weight of at most 3,000 and an HLB value of from 1 to 18 calculated by Griffin's equation The composite of the present invention is produced by applying the powder dispersion of the present invention to the surface of a substrate and heating the powder dispersion.

The valve member according to one embodiment of the present disclosure is a resin formed product having a crosslinked ethylene-tetrafluoroethylene copolymer as a main component, and having a crosslinking density of 85.0 mol/m.sup.3 or more calculated from a storage modulus at 300° C.

The valve member according to one embodiment of the present disclosure is a resin formed product having a crosslinked ethylene-tetrafluoroethylene copolymer as a main component, and having a crosslinking density of 85.0 mol/m.sup.3 or more calculated from a storage modulus at 300° C.

To provide a method for producing a fluorinated polymer which does not require an emulsifier as an essential component while an aqueous medium with little environmental burden is used. A method for producing a fluorinated polymer, which comprises polymerizing at least one fluorinated polymer selected from tetrafluoroethylene, chlorotrifluoroethylene and vinylidene fluoride, in an aqueous medium in the presence of a specific polymer having at least one type of units selected from units based on a compound represented by the formula (1) and units based on a compound represented by the formula (2) to produce a fluorinated polymer (provided that when tetrafluoroethylene is polymerized, tetrafluoroethylene is polymerized so that the content of units based on tetrafluoroethylene in the fluorinated polymer becomes less than 99 mass % to all units in the fluorinated polymer):

CXY═CR.sup.1—COO-(L-O).sub.n—R.sup.2  formula (1):

CXY═CR.sup.3—(O).sub.m—CH.sub.2—Z—R.sup.4  formula (2):

Provided is a fuel filler pipe including: an inner layer that contains a fluorine-containing copolymer having a carbonyl group-containing group and having a melting point of 250° C. or lower; an intermediate layer that contains a non-fluorine copolymer having a unit based on ethylene and a unit based on vinyl alcohol; and an outer layer that contains a polyolefin, wherein the inner layer, the intermediate layer, and the outer layer are directly laminated in that order, and the outer layer is a layer that contains a polyolefin having a unit based on an acid anhydride or is a layer in which a layer that contains a polyolefin having a unit based on an acid anhydride and a layer that contains a polyolefin having no unit based on an acid anhydride are directly laminated.

Provided is a fuel filler pipe including: an inner layer that contains a fluorine-containing copolymer having a carbonyl group-containing group and having a melting point of 250° C. or lower; an intermediate layer that contains a non-fluorine copolymer having a unit based on ethylene and a unit based on vinyl alcohol; and an outer layer that contains a polyolefin, wherein the inner layer, the intermediate layer, and the outer layer are directly laminated in that order, and the outer layer is a layer that contains a polyolefin having a unit based on an acid anhydride or is a layer in which a layer that contains a polyolefin having a unit based on an acid anhydride and a layer that contains a polyolefin having no unit based on an acid anhydride are directly laminated.

A method for producing a modified polytetrafluoroethylene, the method including: polymerizing tetrafluoroethylene in an aqueous medium in which a polymer having units based on a fluorine-free monomer is present. The fluorine-free monomer is a monomer represented by formula (1): CH.sub.2═CR.sup.1-L-R.sup.2, where R.sup.1 is a hydrogen atom or an alkyl group, L is a single bond, —CO—O—*, —O—CO—* or —O—, * is a bonding position to R.sup.2, and R.sup.2 is an alkyl group. To the total amount of tetrafluoroethylene supplied to the polymerization, a proportion of the polymer is from 0.001 to 0.050 mass %.

To provide a fluorinated copolymer composition whereby a crosslinked rubber article which has a low compression set at high temperature and which is not broken after compression can be formed, and a crosslinked rubber article.

The fluorinated copolymer composition of the present invention comprises a fluorinated copolymer having nitrile groups, a phosphorus compound having a melting point of 60° C. or lower and a crosslinking agent.