To provide a liquid composition with which a catalyst layer and a polymer electrolyte membrane will hardly be broken at the time of their formation and a method for producing the liquid composition; and a method for producing a membrane/electrode assembly by which a catalyst layer and a polymer electrolyte membrane will hardly be broken at the time of their formation. A liquid composition comprising a polymer having ion exchange groups, water and an organic solvent, wherein the average secondary particle size of the polymer having ion exchange groups is from 100 to 3,000 nm, and the primary particle size parameter represented by the product of the average primary particle size (nm) and the ion exchange capacity (meq/g dry resin) of the polymer having ion exchange groups, is from 12 to 20.

To provide a liquid composition with which a catalyst layer and a polymer electrolyte membrane will hardly be broken at the time of their formation and a method for producing the liquid composition; and a method for producing a membrane/electrode assembly by which a catalyst layer and a polymer electrolyte membrane will hardly be broken at the time of their formation. A liquid composition comprising a polymer having ion exchange groups, water and an organic solvent, wherein the average secondary particle size of the polymer having ion exchange groups is from 100 to 3,000 nm, and the primary particle size parameter represented by the product of the average primary particle size (nm) and the ion exchange capacity (meq/g dry resin) of the polymer having ion exchange groups, is from 12 to 20.

A compound represented by the formula (I): ##STR00001##

A compound represented by the formula (I): ##STR00001##

A method for producing a fluoropolymer which includes polymerizing a fluoromonomer in an aqueous medium in the presence of a surfactant to provide a fluoropolymer, the surfactant being represented by the general formula (1): CR.sup.1R.sup.2R.sup.4—CR.sup.3R.sup.5—X-A, wherein R.sup.1 to R.sup.5 are each H or a monovalent substituent, with the proviso that at least one of R.sup.1 and R.sup.3 represents a group represented by the general formula: —Y—R.sup.6 and at least one of R.sup.2 and R.sup.5 represents a group represented by the general formula: —X-A or a group represented by the general formula: —Y—R.sup.6; and A is the same or different at each occurrence and is —COOM, —SO.sub.3M, or —OSO.sub.3M. Also disclosed is a surfactant for polymerization represented by the general formula (1), a method for producing a fluoropolymer using the surfactant and a composition including a fluoropolymer and the surfactant.

A method for producing a fluoropolymer which includes polymerizing a fluoromonomer in an aqueous medium in the presence of a surfactant to provide a fluoropolymer, the surfactant being represented by the general formula (1): CR.sup.1R.sup.2R.sup.4—CR.sup.3R.sup.5—X-A, wherein R.sup.1 to R.sup.5 are each H or a monovalent substituent, with the proviso that at least one of R.sup.1 and R.sup.3 represents a group represented by the general formula: —Y—R.sup.6 and at least one of R.sup.2 and R.sup.5 represents a group represented by the general formula: —X-A or a group represented by the general formula: —Y—R.sup.6; and A is the same or different at each occurrence and is —COOM, —SO.sub.3M, or —OSO.sub.3M. Also disclosed is a surfactant for polymerization represented by the general formula (1), a method for producing a fluoropolymer using the surfactant and a composition including a fluoropolymer and the surfactant.

A variation in the performance value of a polymer being manufactured can be reduced. A prediction device (10A) that, in manufacturing of a polymer, predicts a performance value indicating performance of the polymer in a polymerization tank after a raw material is fed, and may include: an acquisition unit (111) that acquires, as a prediction observation value, an observation value observed, in current manufacturing of the polymer, as a value related to the manufacturing of the polymer; and a prediction unit (112) that predicts the performance value of the polymer being currently manufactured at a predetermined timing, from the prediction observation value acquired by the acquisition unit, by using a relation between an observation value acquired in past manufacturing of the same type of polymer as the polymer, and a performance value of the polymer at the predetermined timing in the past manufacturing.

A variation in the performance value of a polymer being manufactured can be reduced. A prediction device (10A) that, in manufacturing of a polymer, predicts a performance value indicating performance of the polymer in a polymerization tank after a raw material is fed, and may include: an acquisition unit (111) that acquires, as a prediction observation value, an observation value observed, in current manufacturing of the polymer, as a value related to the manufacturing of the polymer; and a prediction unit (112) that predicts the performance value of the polymer being currently manufactured at a predetermined timing, from the prediction observation value acquired by the acquisition unit, by using a relation between an observation value acquired in past manufacturing of the same type of polymer as the polymer, and a performance value of the polymer at the predetermined timing in the past manufacturing.

A variation in the performance value of a polymer being manufactured can be reduced. A prediction device (10A) that, in manufacturing of a polymer, predicts a performance value indicating performance of the polymer in a polymerization tank after a raw material is fed, and may include: an acquisition unit (111) that acquires, as a prediction observation value, an observation value observed, in current manufacturing of the polymer, as a value related to the manufacturing of the polymer; and a prediction unit (112) that predicts the performance value of the polymer being currently manufactured at a predetermined timing, from the prediction observation value acquired by the acquisition unit, by using a relation between an observation value acquired in past manufacturing of the same type of polymer as the polymer, and a performance value of the polymer at the predetermined timing in the past manufacturing.

A process is provided for the polymerization of fluoromonomer to an dispersion of fluoropolymer particles in an aqueous medium in a polymerization reactor, by (a) providing the aqueous medium in the reactor, (b) adding the fluoromonomer to the reactor, (c) adding initiator to the aqueous medium, the combination of steps (b) and (c) being carried out essentially free of hydrocarbon-containing surfactant and resulting in the kickoff of the polymerization of the fluoromonomer, and (d) metering hydrocarbon-containing surfactant into the aqueous medium after the kickoff of polymerization, e.g. after the concentration of the fluoropolymer in the aqueous medium is at least 0.6 wt %, the metering being at a rate reducing the telogenic activity of said surfactant while maintaining surface activity.