A method for producing a perfluoroelastomer, which includes carrying out polymerization of a perfluoromonomer in an aqueous medium in the presence of a polymer (1) having a number average molecular weight of 0.310.sup.4 or more to provide a perfluoroelastomer, the polymer (1) containing a polymerized unit (1) derived from a monomer represented by the following general formula (1):
CX.sub.2CY(CZ.sub.2ORf-A)(1)
wherein X, Y, Z, Rf and A are as defined herein, with the proviso that at least one of X, Y, and Z contains a fluorine atom.

A method for producing a perfluoroelastomer, which includes carrying out polymerization of a perfluoromonomer in an aqueous medium in the presence of a polymer (1) having a number average molecular weight of 0.310.sup.4 or more to provide a perfluoroelastomer, the polymer (1) containing a polymerized unit (1) derived from a monomer represented by the following general formula (1):
CX.sub.2CY(CZ.sub.2ORf-A)(1)
wherein X, Y, Z, Rf and A are as defined herein, with the proviso that at least one of X, Y, and Z contains a fluorine atom.

A surfactant for polymerization including at least one selected from a surfactant represented by R.sup.1aCOR.sup.2aCOR.sup.3aOSO.sub.3X.sup.a and a surfactant represented by R.sup.1bCO(CR.sup.2b.sub.2).sub.n(OR.sup.3b).sub.p(CR.sup.4b.sub.2).sub.q-L-OSO.sub.3X.sup.b, wherein R.sup.1a, R.sup.2a, R.sup.3a, X.sup.a, R.sup.1b, R.sup.2b, R.sup.3b, R.sup.4b, L and X.sup.b are as defined herein. Also disclosed is a composition containing a fluoropolymer and the at least one surfactant, a composition containing a fluoropolymer and a compound represented by (H(CF.sub.2).sub.8SO.sub.3).sub.qM.sup.2, where M.sup.2 is as defined herein, and a molded article made from the composition containing a fluoropolymer and the compound represented by (H(CF.sub.2).sub.8SO.sub.3).sub.qM.sup.2.

A surfactant for polymerization including at least one selected from a surfactant represented by R.sup.1aCOR.sup.2aCOR.sup.3aOSO.sub.3X.sup.a and a surfactant represented by R.sup.1bCO(CR.sup.2b.sub.2).sub.n(OR.sup.3b).sub.p(CR.sup.4b.sub.2).sub.q-L-OSO.sub.3X.sup.b, wherein R.sup.1a, R.sup.2a, R.sup.3a, X.sup.a, R.sup.1b, R.sup.2b, R.sup.3b, R.sup.4b, L and X.sup.b are as defined herein. Also disclosed is a composition containing a fluoropolymer and the at least one surfactant, a composition containing a fluoropolymer and a compound represented by (H(CF.sub.2).sub.8SO.sub.3).sub.qM.sup.2, where M.sup.2 is as defined herein, and a molded article made from the composition containing a fluoropolymer and the compound represented by (H(CF.sub.2).sub.8SO.sub.3).sub.qM.sup.2.

A method for producing a fluoropolymer aqueous dispersion, the method comprising: polymerizing a fluoromonomer in the presence of a fluorine-containing surfactant, a polymerization initiator, and an aqueous medium, thereby preparing an aqueous dispersion containing a fluoropolymer; and bubbling a gas containing oxygen into the aqueous dispersion, or bringing the aqueous dispersion into contact with an oxidizing agent, or bringing the aqueous dispersion into contact with an alcohol, thereby obtaining a fluoropolymer aqueous dispersion.

Objects of the present invention are to provide a rubber composition with low haze, a method for producing a rubber composition and a crosslinked rubber article. The rubber composition of the present invention contains a crosslinked product of a fluorinated copolymer, wherein the ratio E2/E1 of a storage modulus E2 of the rubber composition as measured by dynamic mechanical analysis at a measurement temperature of 150 C. and a measurement frequency of 1 Hz, to a storage modulus E1 of the rubber composition as measured by dynamic mechanical analysis at a measurement temperature of 100 C. and a measurement frequency of 1 Hz, is 1.40 or higher.

Objects of the present invention are to provide a rubber composition with low haze, a method for producing a rubber composition and a crosslinked rubber article. The rubber composition of the present invention contains a crosslinked product of a fluorinated copolymer, wherein the ratio E2/E1 of a storage modulus E2 of the rubber composition as measured by dynamic mechanical analysis at a measurement temperature of 150 C. and a measurement frequency of 1 Hz, to a storage modulus E1 of the rubber composition as measured by dynamic mechanical analysis at a measurement temperature of 100 C. and a measurement frequency of 1 Hz, is 1.40 or higher.

A method for producing a fluoropolymer, which includes: polymerizing a monomer (I) represented by the general formula (I) below in an aqueous medium substantially in the absence of a fluorine-containing surfactant (except for the monomer (I) represented by the general formula (I)) to obtain a crude composition containing a polymer of the monomer (I); removing a dimer and a trimer of the monomer (I) contained in the crude composition from the crude composition to obtain a polymer (I) in which the content of the dimer and trimer of the monomer (I) is 1.0% by mass or less based on the polymer (I); and polymerizing a fluoromonomer in an aqueous medium in the presence of the polymer (I) to obtain a fluoropolymer:
CX.sup.1X.sup.3CX.sup.2R(CZ.sup.1Z.sup.2-A.sup.0).sub.m(I)
wherein X.sup.1 and X.sup.3, X.sup.2, A.sup.0, R, Z.sup.1 and Z.sup.2 are as defined herein.

An apparatus suitable for extruding curable polymers for forming elastomer articles using additive manufacturing, and curable fluorine-containing polymer compositions suitable for use in such an apparatus are disclosed along with an additive manufacturing method for forming a fluorine-containing elastomer article including providing a filament formed of a curable fluoropolymer composition; providing an additive manufacturing printer having a drive mechanism and a printer nozzle; feeding the filament into an additive manufacturing printer through the drive mechanism and through a longitudinal passage defined by an interior wall of a support tube, wherein the support tube extends from a first end to a second end, and wherein the second end of the support tube is positioned near an inlet to a printer nozzle; applying heat to the filament; and printing successive layers of the heated filament exiting an outlet of the nozzle onto a substrate using the additive manufacturing printer to form the fluorine-containing elastomer article.

An apparatus suitable for extruding curable polymers for forming elastomer articles using additive manufacturing, and curable fluorine-containing polymer compositions suitable for use in such an apparatus are disclosed along with an additive manufacturing method for forming a fluorine-containing elastomer article including providing a filament formed of a curable fluoropolymer composition; providing an additive manufacturing printer having a drive mechanism and a printer nozzle; feeding the filament into an additive manufacturing printer through the drive mechanism and through a longitudinal passage defined by an interior wall of a support tube, wherein the support tube extends from a first end to a second end, and wherein the second end of the support tube is positioned near an inlet to a printer nozzle; applying heat to the filament; and printing successive layers of the heated filament exiting an outlet of the nozzle onto a substrate using the additive manufacturing printer to form the fluorine-containing elastomer article.