Abstract: In the emulsion obtained by forcedly emulsifying by applying a high shearing force on the water insoluble liquid in the presence of a small amount of emulsifying agent, at least one of fluorine-containing monomers being in the form of gas at ordinary temperature at atmospheric pressure is emulsion-polymerized stably and efficiently. An amount of the emulsifying agent is an amount which does not change the number of water insoluble liquid particles in the emulsion during the polymerization.

Abstract: A peroxide-curable fluorine-containing elastomer composition comprising 100 parts by weight of a fluorine-containing block polymer comprising at least one elastomeric polymer chain segment and at least one non-elastomeric polymer chain segment in which the content of said non-elastomeric polymer chain segment is less than 5% by weight, 0.05 to 10 parts by weight, preferably 0.3 to 5 parts by weight, more preferably 1 to 5 parts by weight, of an organic peroxide, and 0.1 to 10 parts by weight, preferably 0.5 to 8 parts by weight, more preferably 0.5 to 5 parts by weight, of a polyfunctional co-crosslinking agent. This composition has improved processing properties during curing and molding, while it has good tensile properties, heat resistance, oil resistance and high temperature sealing properties comparable to those of conventional peroxide-curable fluorine-containing elastomer compositions.

Abstract: The present invention provides the fluorine-containing elastic copolymer which is excellent in molding processability, particularly molding stability and further vulcanization properties, flowability at molding and compression set of a vulcanized rubber. The copolymer is prepared through emulsion polymerization of vinylidene fluoride and at least one of other monomers in two polymerization stages by using a water-soluble radical polymerization initiator in a very small amount of 0.001 to 0.03% by weight based on the total weight of copolymers prepared in the two stages and an oil-soluble radical polymerization initiator. The present invention also provides a process for preparation thereof and a vulcanizable composition containing the same.