Process for preparing elastomeric copolymers of vinylidene fluoride and the elastomeric copolymers obtained thereby

Claim 1

A process for preparing elastomeric vinylidene fluoride/tetrafluorethylene/1-hydropentafluoroethylene terpolymers containing between about 68% and about 80% in moles of vinylidene fluoride, by polymerizing the three comonomers in solution, emulsion or suspension, or in the absence of solvents and or dispersants (mass or bulk), in the presence of radical initiators, at a temperature of from -30° C. to +200° C. and under a pressure from the autogenous pressure to 300 atms., said process being characterized in that the feeding of the monomeric mixture to the zone in which the terpolymerization is effected is interrupted intermittently, the monomeric mixture is left to polymerize in said zone until the pressure reaches a value comprised between 1/100 and 9/10 of the pre-fixed, normal polymerization pressure, vinylidene fluoride is then fed into said zone until a pressure value comprised between 11/10 and 19/10 of the pre-fixed normal pressure is reached, the monomers mixture thus obtained is left to polymerize in said zone until the normal pressure is reached, and thereafter feeding of the monomers mixture is resumed, the ratio between the vinylidene fluoride fed to the reaction zone alone, as separate monomer, to the vinylidene fluoride fed in the mixture with tetrafluoroethylene and 1-hydropentafluoroethylene being comprised between 0.1 and 1.5.