A fluorine-containing elastomeric copolymer comprising 55 to 62 mole % of repeating units derived from tetrafluoroethylene and 38 to 45 mole % of repeating units derived from perfluoro(methyl vinyl ether) which is obtained by radically polymerizing the monomers in the presence of a diiodide compound of the formula: RI.sub.2 in which R is a saturated fluorohydrocarbon or chlorofluorohydrocarbon group having 1 to 16 carbon atoms, or a hydrocarbon group having 1 to 3 carbon atoms and which has a Mooney viscosity (ML.sub.1+10 100.degree. C.) in the range between 20 and 150. This copolymer has an excellent compression set at high temperature, which is an important property for sealing members.

Perfluoroelastomers characterized by low molecular weight and freedom form color-forming impurities can be prepared by pyrolysis techniques, and are useful in pellicle coatings and other optical applications.

A fluorine-containing elastomer capable of giving a primary vulcanization product with a good permanent set through peroxide vulcanization is produced by homopolymerization or copolymerization of a fluorine-containing olefin having 2 to 8 carbon atoms in the presence of an iodine and bromine-containing compound represented by the general formula RBrnIm, wherein R represents a fluorohydrocarbon group, a chlorofluorohydrocarbon group, a chlorohydrocarbon group or a hydrocarbon group, and n and m each are integers of 1 and 2, and a small amount of perfluoro(vinylether) compound having a general formula of CF.sub.2 .dbd.CFO[CF.sub.2 CF(CF.sub.3)O]m(CF.sub.2)nX, wherein X is a bromine atom or an iodine atom and m and n each are 1, 2 or 3.

A fluorine-containing elastomer capable of giving a primary vulcanization product with a good permanent set through peroxide vulcanization is produced by homopolymerization or copolymerization of a fluorine-containing olefin having 2 to 8 carbon atoms in the presence of an iodine and bromine-containing compound represented by the general formula RBrnIm, wherein R represents a fluorohydrocarbon group, a chlorofluorohydrocarbon group, a chlorohydrocarbon group or a hydrocarbon group, and n and m are integers of 1 and 2, and a small amount of perfluoro(unsaturated compound) which is iodotrifluoroethylene, perfluoro(bromoalkylvinylether) or perfluoro(iodoalkylvinylether).

A novel fluorine-containing copolymer elastomer having bromine groups as cross-linkable groups, which comprises about 45 to about 80% by mole of tetrafluoroethylene, about 50 to about 20% by mole of a perfluoro(vinylether) represented by the following general formula: where n is an integer of 1 to 5, and about 0.2 to about 5% by mole of a bromine-containing unsaturated monomer compound, sum total being 100% by mole, gives vulcanization products having distinguished resistances to chemicals, low temperature and heat.