A polytetrafluoroethylene tube is provided and has a thickness of 0.1 mm or less, a tensile elongation at break of 350% or more, and a melting energy of 0.6 J/g or more which is calculated from an endothermic peak at 370° C.±5° C. in a procedure of increasing a temperature in differential scanning calorimetry (DSC).

Provided is a method for producing a purified fluoropolymer containing less fluoridable end groups. The production method includes: (a) melting a fluoropolymer to give a molten fluoropolymer; (b) reducing a reaction inhibitor in the molten fluoropolymer; (c) bringing the molten fluoropolymer into contact with an active substance after the step (b); and (d) removing a volatile matter from the molten fluoropolymer after the step (c).

Provided is a method for producing a purified fluoropolymer containing less fluoridable end groups. The production method includes: (a) melting a fluoropolymer to give a molten fluoropolymer; (b) reducing a reaction inhibitor in the molten fluoropolymer; (c) bringing the molten fluoropolymer into contact with an active substance after the step (b); and (d) removing a volatile matter from the molten fluoropolymer after the step (c).

The invention pertains to a method for making a fluoropolymer comprising an aqueous emulsion polymerization of one or more fluorinated monomers wherein said aqueous emulsion polymerization is carried out in the presence of at least one cyclic fluorocompound of the following formula (I): ##STR00001##
wherein X.sub.1, X.sub.2, X.sub.3, equal or different from each other are independently selected among H, F, and C.sub.1-6 (per)fluoroalkyl groups, optionally comprising one or more catenary or non-catenary oxygen atoms; L represents a bond or a divalent group; R.sub.F is a divalent fluorinated C.sub.1-3 bridging group; Y is a hydrophilic function selected among anionic functionalities, cationic functionalities and non-ionic functionalities.

The invention pertains to a method for making a fluoropolymer comprising an aqueous emulsion polymerization of one or more fluorinated monomers wherein said aqueous emulsion polymerization is carried out in the presence of at least one cyclic fluorocompound of the following formula (I): ##STR00001##
wherein X.sub.1, X.sub.2, X.sub.3, equal or different from each other are independently selected among H, F, and C.sub.1-6 (per)fluoroalkyl groups, optionally comprising one or more catenary or non-catenary oxygen atoms; L represents a bond or a divalent group; R.sub.F is a divalent fluorinated C.sub.1-3 bridging group; Y is a hydrophilic function selected among anionic functionalities, cationic functionalities and non-ionic functionalities.

A method for producing a fluoropolymer by solution polymerization or dispersion polymerization, the method including: in the presence of an initiator, a chain transfer agent, and a solvent, (i) homopolymerizing tetrafluoroethylene; or (ii) randomly copolymerizing tetrafluoroethylene and at least one of a monomer represented by the following formula (1) or a monomer represented by the following formula (2). The chain transfer agent includes at least one selected from dithioester compounds, dithiocarbamate compounds, trithiocarbonate compounds and xanthate compounds. The fluoropolymer contains 50 to 100 mol % of a polymerized unit based on the tetrafluoroethylene. The formula (1): CF.sub.2═CR.sup.1R.sup.2 wherein R.sup.1 and R.sup.2 are as defined herein, the formula (2): CH.sub.2═CR.sup.3R.sup.4 wherein R.sup.3 and R.sup.4 are as defined herein.

A method for producing a fluoropolymer by solution polymerization or dispersion polymerization, the method including: in the presence of an initiator, a chain transfer agent, and a solvent, (i) homopolymerizing tetrafluoroethylene; or (ii) randomly copolymerizing tetrafluoroethylene and at least one of a monomer represented by the following formula (1) or a monomer represented by the following formula (2). The chain transfer agent includes at least one selected from dithioester compounds, dithiocarbamate compounds, trithiocarbonate compounds and xanthate compounds. The fluoropolymer contains 50 to 100 mol % of a polymerized unit based on the tetrafluoroethylene. The formula (1): CF.sub.2═CR.sup.1R.sup.2 wherein R.sup.1 and R.sup.2 are as defined herein, the formula (2): CH.sub.2═CR.sup.3R.sup.4 wherein R.sup.3 and R.sup.4 are as defined herein.

A multi-acid polymer disclosed herein has the formula

##STR00001##

wherein R is one or more units of a non-SOF.sub.2 or non-SO.sub.2Cl portion of a polymer precursor in sulfonyl fluoride or sulfonyl chloride form, X is a non-sulfonyl halide group of a multi-sulfonyl halide compound having a minimum of two acid giving groups, and Y is remaining sulfonyl halide groups of the multi-sulfonyl halide compound.

A multi-acid polymer disclosed herein has the formula

##STR00001##

wherein R is one or more units of a non-SOF.sub.2 or non-SO.sub.2Cl portion of a polymer precursor in sulfonyl fluoride or sulfonyl chloride form, X is a non-sulfonyl halide group of a multi-sulfonyl halide compound having a minimum of two acid giving groups, and Y is remaining sulfonyl halide groups of the multi-sulfonyl halide compound.

A composition comprising a mixture of fluoropolyether acids or salts having a number average value of about 800 to about 2500 g/mol. The amount of fluoropolyether acids or salt in the mixture having a molecular weight of not more than 500 g/mol is not more than 50 ppm by weight of the total amount of fluoropolyether acids or salts in the mixture. The amount of fluoropolyether acids or salts in the mixture having a molecular weight of 2500 g/mol or greater is not more than 40% by weight of the total amount of fluoropolyether acids or salts in the mixture. Preferably the fluoropolyether acids or salts comprise an anionic group selected from the group consisting of carboxylate, sulfonate, sulfonamide anion and phosphonate. Also disclosed is an aqueous dispersion polymerization process for fluoropolymer manufacture employing polymerization agent comprising the specified mixture of fluoropolyether acids or salts.