Amorphous perfluorinated copolymers

Amorphous perfluorinated copolymers, comprising cyclic perfluorinated units deriving from at least two different perfluorinated comonomers, optionally with units deriving from a non cyclic perfluorinated monomer, or which does not cyclize during the polymerization, containing at least one olefinic unsaturation (perfluoroolefin), or comprising cyclic perfluorinated units and units deriving from a non cyclic perfluorinated monomer, or which does not cyclize during the polymerization, containing at least one olefinic unsaturation, said perfluorinated copolymers having the following combination of properties:

• substantial absence of unstable polar end groups, in particular end groups as COF, COOH or their amidic derivatives, esters or salts;
• said end groups being not detectable in the copolymer, i.e. present in an amount lower than 0.05 mmoles/kg polymer when they are determined by Fourier transform IR spectroscopy by Nicolet® Nexus FT-IR equipment (256 scannings, resolution 2 cm−1), wherein:
• on a sintered polymer powder pellet having 5 mm diameter and thickness from 50 to 300 micron (corresponding to a weight of 1.75 and 10.5 mg of polymer, respectively) a scanning between 4,000 cm−1 and 400 cm−1 is initially carried out, the pellet being then kept for 12 hours in an environment saturated with ammonia vapours;
• the IR spectrum is finally recorded under the same conditions of the initial IR spectrum;
• the two spectra are elaborated by subtracting from the signals of the spectrum relating to the untreated sample (initial spectrum) those corresponding to the specimen spectrum after exposure to ammonia vapours;
• the “difference” spectrum is obtained, which is normalized by the following equation:
• 3 `` ⁢ Difference ⁢ ⁢ spectrum ″ [ pellet ⁢ ⁢ weight ⁢ ⁢ ( g ) / pellet ⁢ ⁢ area ⁢ ⁢ ( cm 2 ⁢ ) ]
• the optical densities related to the end groups which have reacted with the ammonia vapours are measured, which give rise to detectable peaks in the IR spectrum, said end groups being the COOH and COF groups;
• the optical densities are converted in mmoles/kg polymer using the extinction coefficients shown in Table 1, page 73 of the paper by M. Pianca et Al. “End groups in fluoropolymers”, J. Fluorine Chem. 95 (1999), 71-84 (herein incorporated by reference);
• the so found values give the concentrations of the residual polar end groups as mmoles of polar end groups/kg polymer:
• in the spectrum of the amorphous (per)fluorinated polymers after fluorination bands related to COOH groups (3,600-3,500, 1,820-1,770 cm−1) and/or COF groups (1,900-1,830 cm−1) are not detectable, the method detectability limit being 0.05 mmoles/Kg polymer;
• polymer Tg higher than 120° C., preferably 125° C.;
• narrow distribution of the monomeric composition of the amorphous perfluorinated copolymer measured according to the following test:
• the polymer is dissolved at a concentration of 5% w/w in perfluoroheptane solvent, after filtration on PTFE filter having a maximum pore diameter of 0.2 micron, no polymer residue remains on the filter whereby the filter weight before and after filtration remains unchanged.