The present invention concerns a radical polymerization method for preparing halogenated polymers, using one or more ethylenically unsaturated monomers whereof at least one is selected among halogenated monomers, molecular iodine and one or more radical generating agents selected among diazo-compounds, peroxides and dialkyldiphenylalkanes. The present invention also concerns a method for radical polymerization, starting with halogenated polymers prepared by the above method, of block copolymers whereof at least one block is a halogenated polymer block. The invention further concerns halogenated polymers having a number average molecular weight Mn greater than 1.0*10<4> and a Mz/Mw ratio less than 1.65. The invention also concerns block copolymers whereof at least one is a halogenated polymer block identical to said halogenated polymers above. Finally, the invention concerns block copolymers comprising at least one halogenated polymer block having a number average molecular weight Mn greater than 1.5*10<4> and polydispersity index Mw/Mn less than 1.60.