New perfluoropolyethers comprising repeating units chosen from among ##STR1## statistically distributed along the chain, having a controlled molecular weight and brominated end groups, prepared starting from the product of the photochemical oxidation of C.sub.2 F.sub.4, and/or C.sub.3 F.sub.6, containing peroxidic oxygen, and subsequent treatment in liquid phase with bromine, at temperatures ranging from -40.degree. to 130.degree. C. in the presence of ultraviolet radiations, said new perfluoropolyethers derivatives being useful as additives in rubber mixes vulcanizable with peroxides, in amounts of 0.01 to 5 parts by w per 100 parts by weight of elastomer, optionally in combination with non brominated perfluoropolyethers, to improve the processability in the extrusion and the detachability of the vulcanized articles from the molding.
This is a divisional of application Ser. No. 07/251,356 filed Sep. 30, 1988 which in turn is a combination of application Ser. No. 832,735, filed Feb. 25, 1986 and Ser. No. 917,550 filed Oct. 10, 1986.
Priority Data
Feb 26, 1985 [IT] 19653 A/85 Oct 16, 1985 [IT] 22517 A/85 Oct 17, 1985 [IT] 22532 A/85
Process for preparing perfluoropolyethers with bromo- or iodo- containing end groups, respectively, by subjecting a peroxidic perfluoropolyether to thermal treatment, in the absence of UV radiation, at temperatures from 120.degree. C. to 280.degree. C. in the presence of bromo- or iodo-containing compounds having, respectively, the following general formulas: wherein T, T', T" equal to or different from each other are selected from Br, F, H or R'.sub.f, wherein R'.sub.f is a perfluoroalkylic chain from 1 to 8 carbon atoms; wherein R, R', R", equal to or different from each other can be I (iodine), H, F, or R'.sub.f, wherein R'.sub.f has the meaning indicated above.
A fluoroelastomer comprising 2 to 8% by mole of tetrafluoroethylene, 14 to 25% by mole of perfluoro(alkyl vinyl ether) and 70 to 85% by mole of vinylidene fluoride, sum total being 100% by mole, obtained by copolymerization in the presence of a bromine-containing monomer compound and an iodine and bromine-containing compound, has distinguished low temperature characteristics, solvent resistance and chemical resistance by itself.
