SSPI 2022/021 Description Perfluoropolyether polymers Cross reference to related patent applications [0001] This patent application claims priority filed on 28 September 2022 in Europe with Nr 22198270.5, the whole content of this application being incorporated herein by reference for all purposes. Technical field [0002] The present invention relates to new copolymers comprising (per)fluoropolyether chains and functional groups. Background Art [0003] (Per)fluoropolyether polymers (in the following referred to as “PFPE polymers”) have been long known as base oils or as additives in several lubricant applications. [0004] Several syntheses of PFPE polymers have been disclosed in the art. The first synthesis of unspecified perfluorinated polyether mixtures was reported in 1953, when an oily product was obtained in the course of photoligomerization of hexafluoropropene. Since then, a number of different perfluorinated polyethers have been synthesised and described in literature. [0005] US 4500739 (in the name of Montedison) discloses the reaction of a peroxidic PFPE with - among the others - perfluoro butadiene (Group II of fluoroolefins). Example 4 discloses the reaction with perfluoro butadiene, with a large excess of perfluorinated bis-olefin, resulting in pendant unsaturated groups along the macromolecular chain such that the reaction can further proceed in the presence of hexamethylenediamine. [0006] US 8,258,090 (in the name of Solvay Solexis S.p.A.) discloses fluorinated lubricants of formula: (I) T-O-[A-B]z-[A’-B’]z’-A-T wherein T and T’ are C1-3 perfluoroalkyl or C1-6 alkyl, A and A are a perfluoropolyether chain, B derives from two different olefins, of which at least one homopolymerizable by radical route, of formula: (Ia) -[(CR ₁ R ₂ -CR ₃ R ₄ ) _j -(CR ₅ R ₆ -CR ₇ R ₈ ) _j’ ]- wherein j is from 1 to 5, j’ is from 0 to 4 and the sum of j+j’ is between 2 and 5; R ₁ to R ₈ are halogen, H, C _1-6 (per)haloalkyl, C _1-6 alkyl, C _1-6 oxy(per)fluoroalkyl; z is higher than or equal to 2, z’ is an integer and the sum of z and z’ is such that the number average molecular weight of the polymer of formula (I) is in the range 500-500000; B’ is (Ia) but at least one of R1 to R8 has a meaning different from that in B. [0007] This patent discloses block copolymers characterised by a linear backbone, without any branching. Indeed, no branching is obtained within B, notably comprising (per)fluoropolyether chains. [0008] PFPE polymers comprising functional groups along the backbone have been disclosed in the art, being useful as reactive intermediate compounds and as additives. SSPI 2022/021 [0009] Perfluoropolyether polymers obtained from the reaction of polyperoxidic perfluoropolyether and fluorinated olefin in the presence of U.V. radiation have been disclosed in US 4,500,739 (Montedison S.p.A., February 19, 1985). [0010] US 6,403,539 (Ausimont S.p.A., June 11, 2002) discloses perfluoro-polyether polymers containing sulphonyl fluoride groups pending along the backbone. This patent application discloses a process wherein the sulphonyl fluoride-containing monomer is contemporaneously fed with an O ₂ flow in a liquid reaction medium, thus obtaining perfluoropolyethers containing in the chain peroxidic groups. However, the presence of the peroxidic groups is not desired for safety concerns. Hence, this patent application discloses that to obtain non peroxidic products without chain scission, the peroxidic perfluoropolyethers are subjected to a thermal treatment at temperatures generally in the range from 150°C to 250°C or to a photochemical treatment, optionally in the presence of a solvent. The process herein disclosed – in which the functionalized monomer is added at the beginning of the polymerization - does not allow the synthesis of a polymer having segregated blocks from the functionalized monomer but rather it allows for the synthesis of a PFPE polymer having randomly distributed functional groups. [0011] Polyfunctional (per)fluoropolyether polymers have been further disclosed in US 5,719,259 (E.I. DuPont de Nemours and Company, February 17, 1998), US 4,853,097 (Ausimont S.r.l., August 1, 1989), US 5,104,911 (Ausimont S.r.l., April 14, 1992). [0012] US 2011/0230631 (Solvay Solexis S.p.A, September 22, 2011) discloses (per)fluoropolyethers comprising at least one (per)fluoropolyoxyalkylene chain comprising at least one recurring unit of formula -CF ₂ -CF(CF ₂ O-SO ₂ F)-O-, wherein fluorosulfate group in brackets is a pendant group, which is subsequently reacted with a nucleophilic agent to provide functional groups, such as notably carboxylic acid, acyl fluoride, amide and esters. [0013] CN 103724559 (ZHONGHAO CHENGUANG RES INST CHEMICAL IND, April 16, 2014) discloses a method comprising placing the perfluoropolyether peroxide prepared by a photo-oxidation method in an inert fluorine-containing solvent, introducing perfluoro-olefin under an ultraviolet irradiation condition, and reacting the perfluoro-olefin with the peroxide to form a stable perfluoropolyether compound. [0014] WO 2019/048394 (Solvay Specialty Polymers Italy S.p.A., March 14, 2019) discloses polyfunctional perfluoropolyether derivatives including a plurality of ionisable groups selected from the group consisting of -SO3Xa, -PO3Xa and – COOXa, wherein Xa is H, ammonium group or a monovalent metal. Summary of invention [0015] The Applicant developed new co-polymers comprising (per)fluoropolyether chains and (per)fluorinated co-monomers, whose properties - for example with respect to their viscosity and/or physical appearance - can be properly tuned based on their intended final use. [0016] More in particular, the Applicant faced the problem of preparing new co-polymers comprising (per)fluoropolyether chains characterised by increased viscosity (as measured by complex viscosity at 0.1 rad/s at 25°C). [0017] According to an embodiment, the new copolymers according to the present invention show a low glass transition temperature (T _g ) and are in the liquid state at room temperature. However, if desired, the new copolymers according to the present invention can be provided in a solid form, such as in particular as rubbers, or in a semi-solid form. [0018] Furthermore, the Applicant developed new copolymers comprising functional groups, which can be advantageously introduced as pendant groups along the main backbone of the PFPE copolymers to make them suitable for use as SSPI 2022/021 additives in different technical fields, including as anti-rust, anti-wear, to increase compatibility among base oils and thickeners and other ingredients dispersed in such base oils. Detailed description of the invention [0019] For the purpose of the present description and of the following claims: - the use of parentheses around symbols or numbers identifying the formulae, for example in expressions like “polymer (P)”, etc., has the mere purpose of better distinguishing the symbol or number from the rest of the text and, hence, said parenthesis can also be omitted; - the acronym “PFPE” stands for "perfluoropolyether” and, when used as substantive, is intended to mean either the singular or the plural form, depending on the context; - the term “functionality (F)” is intended to indicate the amount of functional groups in the copolymer according to the present invention as measured via NMR or titration. [0020] In a first aspect, the present invention relates to a block copolymer [copolymer (P)] comprising a first and a second perfluoropolyether chain [PFPE chain] each having two chain ends, wherein the first chain end of each one of said first and second PFPE chain is a chain end of copolymer (P) and each one comprises a group selected from a perfluorinated linear or branched alkyl chain comprising from 1 to 6 carbon atoms, -C(=O)F and -OC(=O)F, and the second chain ends of said first and second PFPE chain are bonded to each other via: – at least one first block [block (1)] complying with formula (I): -[CR ₁₀₀ R ₁₀₁ -CR ₁₀₂ R ₁₀₃ ] _L^ -(D) _L - (I) wherein L^ is 0 or an integer from 1 to 250; R ₁₀₀ , R ₁₀₁ , R ₁₀₂ and R ₁₀₃ are each independently selected from halogen atom, more preferably fluorine or chlorine atom; linear or branched alkyl chain comprising from 1 to 6 carbon atoms; -OR ₂₀₀ wherein R ₂₀₀ is a linear or branched perfluorinated chain comprising from 1 to 6 carbon atoms or a group of formula - CF2OR201 in which R201 is a perfluorinated alkyl chain comprising from 1 to 6 carbon atoms, optionally interrupted by one or more oxygen ether atoms; or one of R100 and R101 and one of R102 and R103 are a fluorine atom and the other of R100 and R101 and the other of R102 and R103 together form a perhalogenated cyclic ring having from 4 to 6 members, optionally comprising heteroatoms, such as oxygen atoms; L is 0 or an integer from 1 to 250, and D is a group of formula -(CR _100* R _101* -CR _102* R _103* )- wherein at least one of R _100* , R101* R102* and R103* is different from R100, R101, R102, and R103, such that (D) is different from -[CR100R101-CR102R103]L^-; with the proviso that, when L^ and L are both different from 0, the recurring units are statistically distributed; – at least one second block [block (2)] complying with formula (II): wherein m is 0 or an integer from 1 to 5; SSPI 2022/021 R ₅ to R ₈ , each independently, is selected in the group comprising, preferably consisting of, -F, perfluorinated linear or branched alkyl chain having from 1 to 6 carbon atoms, and group of formula (III): (III) -R20-(X)y wherein R ₂₀ is a sigma bond, or linear or branched perfluoroalkyl chain comprising from 1 to 12 carbon atoms, preferably comprising and/or interrupted by at least one oxygen atom, X is a functional group, preferably selected from: -SO ₂ F, -SO ₃ H, -COOH, -COF, - CN, -Br and -CONH ₂ ; and y is an integer equal to 1 or 2; with the proviso that in formula (II), at least one, preferably one, of R ₅ to R ₈ is group of formula (III); – at least one third block [block (3)] complying with formula (IV): (IV) wherein n is an integer from 1 to 3; R1 to R4, each independently, is selected in the group comprising, preferably consisting of, fluorine atom, perfluorinated linear or branched alkyl group having from 1 to 6 carbon atoms, group of formula (V): (V) -(R10)t[C(R11)(R12)-C(R13)(R14)(R15)]z wherein R10 is an oxygen atom, or a bi-/tri-/tetravalent perfluorinated alkyl chain comprising from 1 to 24 carbon atoms and being optionally interrupted by at least one oxygen atom, t is zero or 1, z is an integer from 1 to 3, R ₁₁ to R ₁₅ , each independently, is selected in the group comprising, preferably consisting of: fluorine atom, perfluorinated linear or branched alkyl group having from 1 to 6 carbon atoms and group of formula (VI): -[(A) _a -(B) _b -(E)-(F) _f ] _u -(A)-T (VI) wherein u is zero or an integer from 1 to 50; T is a perfluorinated alkyl group; a is zero or 1, each A is a PFPE chain; b is zero or an integer from 1 to 3, B is a block of formula (IV*): -[C(R _1^ )(R _2^ )-C(R _3^ )(R _4^ )]- (IV*) wherein R1^ to R4^ each independently has the meaning defined above for each of R1 to R ₄ , respectively; E is a block of formula (I*) -[CR100^R101^-CR102^R103^]e^-(D*)e*- (I*) wherein e^ has the same meaning provided above for L^, each of R100^ R101^ ,R102^ and R103^ has the same meaning provided above for R ₁₀₀ , R ₁₀₁ , R ₁₀₂ and R ₁₀₃ , respectively, SSPI 2022/021 e* has the same meaning provided above for L, and D* has the same meaning provided above for D, with the proviso that, when e^ and e* are both different from 0, the recurring units are statistically distributed; f is 0 or an integer from 1 to 5, preferably from 1 to 2; F is a block of formula (II*): -[C(R _5^ )(R _6^ )-C(R _7^ )(R _8^ )]- wherein R _5^ to R _8^ , each independently, has the meaning provided above for each of R ₅ to R ₈ , respectively; with the proviso that : - in said formula (IV), at least one of R ₁ to R ₄ is a group of formula (V), - in said formula (IV*), at least one of R1^ to R4^ is a group of formula (V) - in said formula (V), one of R11 or R12 and one of R13 to R15, is a group of formula (VI), - in said formula (VI), the recurring units (A), (B), (E) and (F) are statistically distributed; and – optionally, at least one fourth block [block (4)] comprising a PFPE chain; with the proviso that, in copolymer (P): - the sum of (L+L^+e^+e*) is at least 1, preferably from 1 to 500, more preferably from 2 to 500, more preferably from 2 to 300; - the sum of (m+f) is at least 1, preferably from 1 to 100; - the sum of (n+b) is at least 1, preferably from 1 to 15, more preferably from 1 to 11, even more preferably from 1 to 9; and - said at least one block (1), said at least one block (2), said at least one block (3) and, when present, said at least one block (4) are statistically distributed. [0021] Advantageously, copolymer (P) according to the invention can be provided in liquid form or in semi-solid form. However, when required by the final use, copolymer (P) can also be provided in the form of solid, such as a rubber. [0022] Advantageously, copolymer (P) is characterised by a complex viscosity, measured at 0.1 rad/s and at 25°C, varying in a large range, such as from 10 Pa*s to more than 2000 Pa*s. [0023] It will be understood by those skilled in the art that said first chain end of said first and second PFPE chain correspond to the two chain ends of copolymer (P). [0024] Preferably, in copolymer (P), each of said PFPE chain is a fully fluorinated chain [chain (Rf)] comprising, preferably consists of, repeating units R°, said repeating units being independently selected from the group consisting of: (i) -CFXO-, wherein X is -F or -CF3; (ii) -CFXCFXO-, wherein X, equal or different at each occurrence, is -F or -CF3, with the proviso that at least one of X is -F; (iii) -CF2CF2CF2O-; (iv) -CF ₂ CF ₂ CF ₂ CF ₂ O-; (v) -(CF ₂ ) _j -CFZ-O- wherein j is an integer from 0 to 3 and Z is a group of general formula -O-R(f-a)-T, wherein R(f-a) is a fluoropolyoxyalkene chain comprising a number of repeating units from 0 to 10, said recurring units being chosen among the following : -CFXO- , -CF ₂ CFXO-, -CF ₂ CF ₂ CF ₂ O-, -CF ₂ CF ₂ CF ₂ CF ₂ O-, with each of X being independently -F or -CF3 and T being a C1-C3 perfluoroalkyl alkyl chain. [0025] Preferably, chain (Rf) complies with the following formula: (Rf-I) -[(CFX ¹ O) _g1 (CFX ² CFX ³ O) _g2 (CF ₂ CF ₂ CF ₂ O) _g3 (CF ₂ CF ₂ CF ₂ CF ₂ O) _g4 ]- wherein - X ¹ is independently selected from -F and -CF3, SSPI 2022/021 - X ² , X ³ , equal or different from each other and at each occurrence, are independently -F, -CF3, with the proviso that at least one of X is -F; - g1, g2 , g3, and g4, equal or different from each other, are independently integers ≥0, such that g1+g2+g3+g4 is in the range from 2 to 300, preferably from 2 to 100; should at least two of g1, g2, g3 and g4 be different from zero, the different recurring units are generally statistically distributed along the chain. [0026] More preferably, chain (R _f ) is selected from chains of formula: (Rf-IIA) -[(CF2CF2O)a1(CF2O)a2]- wherein: - a1 and a2 are independently integers ≥ 0 such that the number average molecular weight is between 400 and 100,000 as determined via NMR, preferably between 400 and 50,000; both a1 and a2 are preferably different from zero, with the ratio a1/a2 being preferably comprised between 0.1 and 10; (Rf-IIB) -[(CF2CF2O)b1(CF2O)b2(CF(CF3)O)b3(CF2CF(CF3)O)b4]- wherein: b1, b2, b3, b4, are independently integers ≥ 0 such that the number average molecular weight is between 400 and 100,000 as determined via NMR, preferably between 400 and 50,000; preferably each of b1, b2, b3, b4 are > 0; (Rf-IIC) -[(CF2CF2O)c1(CF2O)c2(CF2(CF2)cwCF2O)c3]- wherein: cw = 1 or 2; c1, c2, and c3 are independently integers ≥ 0 chosen so that the number average molecular weight is between 400 and 100,000 as determined via NMR, preferably between 400 and 50,000; preferably c1, c2 and c3 are all > 0, with the ratio c3/(c1+c2) being generally lower than 0.2. [0027] Still more preferably, chain (R _f ) complies with formula (R _f -III) here below: (R _f -III) -[(CF ₂ CF ₂ O) _a1 (CF ₂ O) _a2 ]- wherein: - a1, and a2 are integers > 0 such that the number average molecular weight is between 400 and 100,000 as determined via NMR, preferably between 400 and 50,000, with the ratio a1/a2 being generally between 0.1 and 10, more preferably between 0.2 and 5. [0028] Preferably, in block (1), at least one of L^ and L is different from 0. [0029] Preferably, in block (1), both L^ and L are different from 0. [0030] Preferably, R ₁₀₀ , R ₁₀₁ , R ₁₀₂ and R ₁₀₃ , each independently, is a halogen atom, such as fluorine atom or chlorine atom. [0031] Preferably, in block (2), m is 0 or an integer from 1 to 2. [0032] Preferably, in block (2), one of R ₅ to R ₈ is a group of formula (V). [0033] Preferably, in block (2), R20 is a sigma bond or a group selected from those of formula (R20-i) to (R20-iv) as defined hereinafter: (R ₂₀ -i) -(CF2)s1-O-(CF2)s2- wherein each of s1 and s2 is independently an integer from 1 to 6, preferably from 1 to 3; (R20-ii) -O-(CF ₂ ) _s3 - wherein s3 is an integer from 1 to 6, preferably from 1 to 5; (R20-iii) -O-R ₄₀₀ -O-R ₄₀₁ - wherein R400 is a linear or branched perfluorinated alkyl chain comprising from 1 to 6, preferably from 1 to 3, carbon atoms, and more preferably complying with formula -CF2-, -CF2CF2-, -CF2CF2CF2-, -CF2CF(CF3)-; and R401 is a linear or branched perfluorinated alkyl chain comprising from 1 to 3 SSPI 2022/021 carbon atoms, more preferably complying with formula -CF ₂ -, -CF ₂ CF ₂ -, - CF(CF2)-; (R20-iv) wherein R500 is a linear perfluorinated alkyl chain comprising from 1 to 6 carbon atoms, preferably from 1 to 3 carbon atoms and optionally interrupted by at least one oxygen atom; R501 is a chain of formula -OR503 wherein R503 is a linear perfluorinated alkyl chain comprising from 1 to 3 carbon atoms; R ₅₀₂ is a linear perfluorinated alkyl chain comprising from 1 to 4 carbon atoms and optionally interrupted by at least one oxygen atom; each of R501 and R502 bonding a group X as defined above. [0034] Preferably, in block (3) and formula (V), R ₁₀ complies with one of the following formulae: (R10-i) -(CF2)d(O)e(CF2O)fRCF(O)e*(CF2)d*(CF2O)f* wherein each of d, d*, e, e*, f and f* is independently zero or 1 and R _CF is either a perfluoroalkyl chain comprising from 1 to 12, preferably from 1 to 8 carbon atoms, optionally interrupted by one or more oxygen atoms (R10-ii) -O-(C3F6O)h–(CF2)i-(C3F6O)j-O- wherein h = j and h + j is from 2 to 6, and i is from 2 to 6. [0035] In a second aspect, the present invention relates to a process [process (P)] for the manufacture of copolymer (P) as defined above. The process according to the present invention can be easily scaled up from laboratory scale to pilot and industrial scale. [0036] Advantageously, copolymer (P) of the present invention is prepared via process (P) comprising at least the following steps : (a) contacting: - at least one perfluoropolyether polymer comprising at least one peroxidic group [PFPE peroxy]; - at least one compound [compound (O)] selected in the group comprising, preferably consisting of: (i) fully halogenated olefin comprising from 2 to 15 carbon atoms; (ii) CF2=CFORf, wherein R _f is a C ₁ -C ₆ (per)fluoroalkyl group, preferably -CF ₃ , -C ₂ F ₅ , -C ₃ F ₇ ; a group C ₁ -C ₁₂ [(per)fluoro]-oxyalkyl comprising catenary oxygen atoms, preferably perfluoro-2- propoxypropyl group; (iii) CF ₂ =CFOCF ₂ OR _f2 wherein R _f2 is selected from the group consisting of C ₁ -C ₆ perfluoro-alkyls; C ₅ -C ₆ cyclic perfluoro-alkyls, and C2-C6 perfluoro-oxy-alkyls, comprising at least one catenary oxygen atom, preferably Rf2 is -CF2CF3, -CF2CF2OCF3, or -CF3; (iv) CF ₂ =CFCF ₂ OR _f7 wherein Rf7 is selected from the group consisting of C1-C6 perfluoro-alkyls, C5-C6 cyclic perfluoro-alkyls, and C ₂ -C ₆ perfluoro-oxy-alkyls, comprising at least one catenary oxygen atom; (v) perfluorodioxoles having formula : SSPI 2022/021 wherein each of Rf3, Rf4, Rf5, Rf6, equal to or different from each other, is independently selected from the group consisting of fluorine atom and C ₁ -C ₆ perfluoroalkyl groups, optionally comprising one or more than one oxygen atom, such as notably -CF3, -C2F5, -C3F7, -OCF3, -OCF2CF2OCF3; - at least one perfluorinated compound of formula (X-p): (X-p) wherein each of R ₂₁ to R ₂₃ is independently -F or perfluorinated linear or branched alkyl chain having from 1 to 6 carbon atoms, R20, X and y are as defined above for formula (III); - at least one perfluorinated compound of formula (XX-p): (XX-p) wherein each of R21 to R23 are as defined above in formula (X-p), each of R ₃₁ to R ₃₃ is independently -F or perfluorinated alkyl group having from 1 to 6 carbon atoms, R10 is an oxygen atom, a perfluorinated alkyl chain comprising from 1 to 24 carbon atoms, optionally interrupted by at least one oxygen atom, t is zero or 1; each of z* and z** is independently 1 or 2; and (b) reacting said PFPE peroxy, said at least one compound of formula (X-p), said at least one compound of formula (XX-p) and at least one compound (O) in the presence of UV radiation or under heating. [0037] An advantage of the process for the manufacture of copolymer (P) according to the present invention is that the amounts of the reactants providing each of block (1), block (2) and block (3) can be tuned and selected a priori based on the desired properties of the final copolymer (P). This is advantageous as selecting a priori the amount of the reactants allows to tune the number of each block (1), block (2) and block (3) in copolymer (P). [0038] In step (a), the order in which the reactants are added is not limited. Accordingly, the PFPE peroxy, the compound of formula (X-p), the compound of formula (XX- p) and the compound (O) can be supplied to the reaction environment in any order. SSPI 2022/021 [0039] Before step (a), the PFPE peroxy can be subjected to partial reduction of the peroxide bonds, for example by chemical reduction or UV treatment or thermal treatment. [0040] Preferably, said PFPE peroxy is a peroxidic perfluoropolyether polymer having two chain ends, each comprising a group selected from a linear or branched perfluorinated alkyl chain comprising from 1 to 6 carbon atoms or -C(=O)F, said two chain ends being bonded to opposite sides of a perfluoropolyether chain [chain (Rf)] comprising, preferably consisting of, repeating units (R°) being independently selected from the group consisting of formulae (i) to (v) as above defined and having a peroxidic content (PO), defined as grams of active oxygen (Mw = 16) in 100 g of PFPE peroxy between 0.1 and 4, preferably between 0.1 and 3.5. [0041] Preferably, in said PFPE peroxy, chain (Rf) complies with formulae (Rf-I), or (Rf- IIA), (Rf-IIB), (Rf-IIC) or (Rf-III) as defined above. [0042] According to a preferred embodiment, step (a) of the process of the present invention is performed with at least one compound (O). [0043] Preferably, said at least one compound (O) is selected in the group comprising, preferably consisting of: (i) fully halogenated olefin comprising from 2 to 10 carbon atoms, preferably from 2 to 8 carbon atoms. More preferably, it is selected in the group comprising: tetrafluoroethylene (TFE), hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE). TFE and HFP being particularly preferred. [0044] When two or more compounds (O) are used, preferably, the first compound (O) is selected from those defined in (i) above and a second compound (O) is selected in the group comprising, more preferably consisting of: (ii) CF ₂ =CFOR _f , wherein Rf is a C1-C6 (per)fluoroalkyl group, preferably -CF3, -C2F5, -C3F7 ; a group C1-C12 [(per)fluoro]-oxyalkyl comprising catenary oxygen atoms, preferably perfluoro-2- propoxypropyl group; (iii) CF2=CFOCF2ORf2 wherein Rf2 is selected from the group consisting of C1-C6 perfluoro-alkyls; C5-C6 cyclic perfluoro-alkyls, and C2-C6 perfluoro-oxy-alkyls, comprising at least one catenary oxygen atom, preferably R _f2 is -CF ₂ CF ₃ , -CF ₂ CF ₂ OCF ₃ , or -CF ₃ ; (iv) CF2=CFCF2ORf7 wherein R _f7 is selected from the group consisting of C ₁ -C ₆ perfluoro-alkyls, C ₅ -C ₆ cyclic perfluoro-alkyls, and C2-C6 perfluoro-oxy-alkyls, comprising at least one catenary oxygen atom; (v) perfluorodioxoles having formula : wherein each of R _f3 , R _f4 , R _f5 , R _f6 , equal to or different from each other, is independently selected from the group consisting of fluorine atom and C ₁ -C ₆ perfluoroalkyl groups, optionally comprising one or more than one oxygen atom, such as notably -CF ₃ , -C ₂ F ₅ , -C ₃ F ₇ , -OCF ₃ , -OCF ₂ CF ₂ OCF ₃ . [0045] Preferably, in said at least one compound of formula (X-p), each of R21, R22 and R23 is -F. SSPI 2022/021 [0046] Preferably, in said compound (X-p), R ₂₀ is a sigma bond or a group selected from those of formula (R20-i) to (R20-iv) as defined hereinafter: (R20-i) -(CF2)s1-O-(CF2)s2- wherein each of s1 and s2 is independently an integer from 1 to 6, preferably from 1 to 3; (R ₂₀ -ii) -O-(CF2)s3- wherein s3 is an integer from 1 to 6, preferably from 1 to 5; (R ₂₀ -iii) -O-R400-O-R401- wherein R400 is a linear or branched perfluorinated alkyl chain comprising from 1 to 6, preferably from 1 to 3, carbon atoms, and more preferably complying with formula -CF ₂ -, -CF ₂ CF ₂ -, -CF ₂ CF ₂ CF ₂ -, -CF ₂ CF(CF ₃ )-; and R401 is a linear or branched perfluorinated alkyl chain comprising from 1 to 3 carbon atoms, more preferably complying with formula -CF2-, -CF2CF2-, - CF(CF ₂ )-; (R20-iv) wherein R ₅₀₀ is a linear perfluorinated alkyl chain comprising from 1 to 6 carbon atoms, preferably from 1 to 3 carbon atoms and optionally interrupted by at least one oxygen atom; R ₅₀₁ is a chain of formula -OR ₅₀₃ wherein R ₅₀₃ is a linear perfluorinated alkyl chain comprising from 1 to 3 carbon atoms; R502 is a linear perfluorinated alkyl chain comprising from 1 to 4 carbon atoms and optionally interrupted by at least one oxygen atom; each of R501 and R502 bonding a group X as defined above. [0047] Preferably, said at least one compound of formula (X-p) is selected in the group comprising, more preferably consisting of : CF2=CFCF2OCF2CF2COOH CF2=CFOCF2COOH CF ₂ =CFO(CF ₂ ) ₅ COOH CF2=CFOCF2CF2OCF2COOH CF ₂ =CFOCF ₂ CF ₂ COOH CF ₂ =CFCF ₂ OCF ₂ CF ₂ COF CF2=CFOCF2COF CF ₂ =CFO(CF ₂ ) ₃ OCF(CF ₃ )COF CF ₂ =CFO(CF ₂ ) ₅ COF CF2=CFOCF2CF(CF3)OCF2CF2CN CF ₂ =CFOCF ₂ CN CF2=CFO(CF2)5CN CF2=CFO(CF2)3OCF(CF3)CN CF ₂ =CFCF ₂ OCF ₂ CF ₂ CN CF2=CFOCF2CF2Br CF2=CFCF2OCF2CF2Br CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ CF ₂ Br CF2=CFCF2OCF2CF2CONH2 SSPI 2022/021 CF ₂ =CFOCF ₂ CONH ₂ CF2=CFOCF2CF2CONH2 CF2=CFOCF2CF2SO2F CF2=CFSO2F CF2=CFOCF2CF(SO2F)2 CF ₂ =CFOCF ₂ CF(CF ₂ OCF2CF2SO ₂ F)(OCF ₂ CF ₂ SO ₂ F) CF ₂ =CFOCF ₂ CF(CF ₂ CF ₂ SO ₂ F)(OCF ₂ CF ₂ SO ₂ F) CF2=CFOCF2OCF2CF(CF2OCF2CF2SO2F)(SO2F). [0048] Some exemplary compounds of formula (X-p) and the preparation thereof are provided in WO 03/106515 (in the name of Daikin Ind.), JP 2017-025242 (in the name of ASAHI GLASS CO., LTD.) and in US 2008/138685 (in the name of AGC Inc.). [0049] Preferably, in said compound of formula (XX-p), when t is 1, the one, two, three or four unsaturated moieties are bonded to the same or different atoms, preferably carbon atoms, belonging to R ₁₀ . [0050] Preferably, said at least one compound of formula (XX-p) complies with the following formula: CF ₂ =CF(R ₁₀ ) _t CF=CF ₂ wherein t is zero or 1, and R10 complies with one of the following formulae: (R ₁₀ -i) -(CF ₂ ) _d (O) _e (CF ₂ O) _f R _CF (O) _e* (CF ₂ ) _d* (CF2O) _f* wherein each of d, d*, e, e*, f and f* is independently zero or 1 and R _CF is either a perfluoroalkyl chain comprising from 1 to 12, preferably from 1 to 8 carbon atoms, optionally interrupted by one or more oxygen atoms (R ₁₀ -ii) -O-(C ₃ F ₆ O) _h –(CF ₂ ) _i -(C ₃ F ₆ O) _j -O- wherein h = j and h + j is from 2 to 6, and i is from 2 to 6. [0051] According to a particularly preferred embodiment, said at least one compound of formula (XX-p) complies with the following formula: CF ₂ =CF(R ₁₀ ) _t CF=CF ₂ wherein t is 1 and R ₁₀ complies with formula: (R10-i) -(CF2)d(O)e(CF2O)fRCF(O)e*(CF2)d*(CF2O)f* wherein d, f, d* and f* are zero, e and e* are 1, and RCF is a linear perfluoroalkyl chain comprising from 1 to 10, preferably from 1 to 8 carbon atoms. [0052] Preferably, said compound of formula (XX-p) is selected from the group comprising, more preferably consisting of: CF ₂ =CFCF=CF ₂ CF2=CFOCF=CF2 CF ₂ =CFCF ₂ OCF ₂ CF=CF ₂ CF ₂ =CFO-(CF ₂ ) ₃ CF=CF ₂ CF2=CFCF2O(CF2)3OCF2-CF=CF2 CF ₂ =CFCF ₂ CF=CF ₂ CF ₂ =CF(CF ₂ ) ₂ CF=CF ₂ CF2=CF(CF2)3CF=CF2 CF ₂ =CF(CF ₂ ) ₄ CF=CF ₂ CF2=CFOCF2OCF=CF2 CF2=CFO(CF2)2OCF=CF2 CF ₂ =CFO(CF ₂ ) ₃ OCF=CF ₂ CF2=CFO(CF2)4OCF=CF2 CF2=CF(CF2)2OCF=CF2 SSPI 2022/021 wherein h and j are the same and their sum is from 2 to 6 and i is from 2 to 6. [0053] The amount of each of said at least one compound (X-p), compound (XX-p) and compound (O) is not limited. As explained above, the amount of each of the above mentioned compounds can advantageously be selected based on both the amount of the PFPE peroxy, as well as its peroxidic content, and the properties desired in the final copolymer (P). [0054] For example, the equivalents of double bonds of said compound (X-p) to the equivalents of peroxidic groups preferably range from 1:100 to 5000:100. Also, the equivalents of double bonds of said compound (XX-p) to the equivalents of peroxidic groups preferably range from 1:100 to 100:100. [0055] Step (a) of process (P) can be advantageously performed by contacting said PFPE peroxy with one compound of formula (X-p). [0056] Alternatively, said step (a) can be performed by contacting said PFPE peroxy with two or more compounds of formula (X-p). [0057] Step (a) of process (P) can be advantageously performed by contacting said PFPE peroxy with one compound of formula (XX-p). [0058] Alternatively, said step (a) can be performed by contacting said PFPE peroxy with two or more compounds of formula (XX-p). [0059] Step (a) and step (b) can be performed in the presence of a fluorinated solvent. [0060] Preferably said fluorinated solvent is selected in the group comprising: perfluorocarbons, hydrofluorocarbons, perfluoropolyethers, hydrofluoro- polyethers. [0061] Preferably, step (b) is performed in the presence of UV radiation for a time from 2 to 150 hours, more preferably from 5 to 100 hours. [0062] Preferably, step (b) is performed in the presence of UV radiation at a temperature from -60°C to +150°C, more preferably from -20°C to +100°C and even more preferably from 0°C to 60°C. [0063] As an alternative, step (b) can be performed under thermal treatment, preferably by heating at a temperature from 150 °C to 250 °C. [0064] Preferably, said step (b) is performed in an inert atmosphere. [0065] In a third aspect, the present invention relates to copolymer (P) obtained via process (P) as described above. [0066] Advantageously, the functional groups introduced as pendant groups in block (3) of copolymer (P), such as notably -SO2F, -SO3H, -COOH, -COF, -CN, -Br and - CONH ₂ , as well as the functional groups at the chain ends of copolymer (P), such as notably -COF and -OC(O)F, can be properly reacted to obtain other different functional groups. [0067] The expression “can be reacted” is intended to indicate that such functional groups can for example be salified, hydrolyzed, reduced, oxidised, or undergo a SSPI 2022/021 different chemical reaction to provide functional group(s) endowed with the desired reactivity, taking into consideration the final use of copolymer (P). [0068] Advantageously, copolymer (PF) according to the present invention is obtained from process (P) as described above, which further comprises after said step (b) , at least one step (c) comprising at least one of salification, hydrolyzation, oxidation, reduction or another chemical reaction capable of providing functional group(s) of interest. [0069] The present invention further encompasses copolymer (PF) obtained at the end of step (c) of process (P). [0070] Hence, the present invention encompasses a block copolymer [copolymer (P _F )] comprising a first and a second perfluoropolyether chain [PFPE chain] each having two chain ends, wherein the first chain end of each one of said first and second PFPE chain is a chain end of copolymer (P) and each one comprises a group selected from a perfluorinated linear or branched alkyl chain comprising from 1 to 6 carbon atoms, -COOH and salts thereof with an organic cation, preferably onium cation, more preferably ammonium, or an inorganic cation, preferably an alkaline metal, more preferably Na ⁺ , K ⁺ ; -COOR wherein R is a linear or branched alkyl chain comprising from 1 to 6 carbon atoms, preferably from 1 to 3 carbon atoms, more preferably 1 carbon atoms; -COF; -CONH2; - CON(R300)(R301) wherein each of R300 and R301 have the same meanings defined for R; -(R) _c OH with c being 0 or 1 and R being as defined above; -C(O)-O-C(O)R with R being as defined above; with the proviso that (i) at least one chain end of said first and second PFPE chain comprises a group different from a perfluorinated linear or branched alkyl chain having from 1 to 6 carbon atoms and (ii) when one chain end comprises group -COF, the other chain end does not comprises a perfluorinated linear or branched alkyl chain having from 1 to 6 carbon atoms or -COF; and the second chain ends of said first and second PFPE chain are bonded to each other via: – at least one first block [block (1)] complying with formula (I): -[CR100R101-CR102R103]L^-(D)L- (I) wherein L^, L, D, R100, R101, R102 and R103 have the meanings defined above; – at least one second block [block (2)] complying with formula (II): wherein m, R ₅ to R ₈ , have the meanings defined above; – at least one third block [block (3)] complying with formula (IV): (IV) wherein n, R ₁ to R ₄ , have the meanings defined above; SSPI 2022/021 and – optionally, at least one fourth block [block (4)] comprising a PFPE chain; with the proviso that, in copolymer (PF): - the sum of (L+L^+e^+e*) is at least 1, preferably from 1 to 500, more preferably from 2 to 500, more preferably from 2 to 300; - the sum of (m+f) is at least 1, preferably from 1 to 100; - the sum of (n+b) is at least 1, preferably from 1 to 15, more preferably from 1 to 11, even more preferably from 1 to 9; and - said at least one block (1), said at least one block (2), said at least one block (3) and, when present, said at least one block (4) are statistically distributed. [0071] In another aspect, the present invention relates to a mixture [mixture (PF)] comprising two or more copolymers (P _F ) as defined above. [0072] While purification steps can be performed after any of step (b) and/or step (c) of said process (P), mixtures of copolymers (P) or copolymers (PF) according to the present invention are typically obtained. [0073] Thus, in a further aspect, the present invention relates to a mixture [mixture (P)] comprising two or more copolymers (P) as defined above. [0074] It will be clear to those skilled in the art that mixture (P) is obtained via process (P) as described above. [0075] Advantageously, said mixture (P) can be subjected to one or more purification steps (also referred to as “fractionation” steps), thus obtaining separate copolymers (P) characterised by different viscosities and/or number average molecular weights as measured by ¹⁹ F-NMR and/or functionality (F), preferably from 3 to 102. [0076] Said mixtures can further contain the PFPE peroxy used as starting material and/or mixtures of copolymers (P) containing peroxy groups [copolymer (P _O-O )] and/or mixtures of copolymers (P _F ) containing peroxy groups [copolymers (P _F-O-O )] can be obtained. [0077] In another aspect, the present invention related to a mixture [mixture (M1)] comprising at least one copolymer (P) as defined above, and at least one of said PFPE peroxy used as starting material and/or one or more of copolymers (PO-O). [0078] In another aspect, the present invention relates to a mixture [mixture (M2)] comprising at least one copolymer (PF) as defined above, and at least one of at least one of copolymer (P) as defined above, said PFPE peroxy used as starting material, said one or more copolymers (P _O-O ), and/or said one or more copolymers (PF-O-O). [0079] Advantageously, copolymer (PO-O) and/or copolymer (PF-O-O) can be isolated and used as intermediate in other processes. [0080] While the amount of peroxy groups that can be present in the mixture containing copolymer (P) or copolymer (PF) of the present invention can be up to 99% based on the amount of the starting peroxy groups in the PFPE peroxy, depending on the final application the amount of said peroxy groups can be properly adjusted for example up to 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5%. [0081] More preferably, the amount of said peroxy groups is up to 1, even more preferably up to 0.5 % and still more preferably up to 0.1%. [0082] In another aspect, the present invention relates to a block copolymer [copolymer (PO-O)] comprising a first and a second perfluoropolyether chain [PFPE chain], wherein each of said first and second PFPE chain is a chain (Rf) as defined above or is a chain (RfO-O) wherein (RfO-O) is a repeating units complying with any one of formulae (i) to (v) as defined above for (R°) and having a peroxidic content (PO), defined as grams of active oxygen (Mw = 16) in 100 g of PFPE peroxy between 0.1 and 4, preferably between 0.1 and 3.5, each of said first and second PFPE chain having two chain ends, wherein the first chain end of each one of SSPI 2022/021 said first and second PFPE chain is a chain end of copolymer (P) and each one comprises a group selected from a perfluorinated linear or branched alkyl chain comprising from 1 to 6 carbon atoms, -C(=O)F and -OC(=O)F; and the second chain ends of said first and second PFPE chain are bonded to each other via: – at least one first block [block (1)] complying with formula (I) as defined above; – at least one second block [block (2)] complying with formula (II) as defined above; – at least one third block [block (3)] complying with formula (IV) as defined above; and/or – optionally, at least one fourth block [block (4)] comprising a PFPE chain as defined above; with the proviso that * in copolymer (PO-O) – said block (1), said block (2), said block (3) and, when present, said at least one block (4) are statistically distributed, – the sum of (n+b) is at least 1, preferably from 1 to 15, more preferably from 1 to 11, even more preferably from 1 to 9; – the sum of (L+L^+e^+e*) is at least 1, preferably from 1 to 500, more preferably from 2 to 500, more preferably from 2 to 300; – the sum of (m+f) is at least 1, preferably from 1 to 100. [0083] In a still another embodiment, the present invention relates to a block copolymer [copolymer (PF-O-O)] comprising comprising a first and a second perfluoropolyether chain [PFPE chain], wherein each of said first and second PFPE chain is a chain (Rf) as defined above or is a chain (Rf _O-O ) wherein (Rf _O-O ) is a repeating units complying with any one of formulae (i) to (v) as defined above for (R°) and having a peroxidic content (PO), defined as grams of active oxygen (Mw = 16) in 100 g of PFPE peroxy between 0.1 and 4, preferably between 0.1 and 3.5, each of said first and second PFPE chain having two chain ends, wherein the first chain end of each one of said first and second PFPE chain is a chain end of copolymer (P) and each one comprises a group selected from a perfluorinated linear or branched alkyl chain comprising from 1 to 6 carbon atoms, -COOH and salts thereof with an organic cation, preferably onium cation, more preferably ammonium, or an inorganic cation, preferably an alkaline metal, more preferably Na ⁺ , K ⁺ ; -COOR with R being as defined above; -COF; -CON(R300)(R301) wherein each of R ₃₀₀ and R ₃₀₁ are a hydrogen atom or have the same meanings defined for R; -(R)cOH with c being 0 or 1 and R being as defined above; -C(O)-O-C(O)R with R being as defined above; -Br; -CN2; and the second chain ends of said first and second PFPE chain are bonded to each other via: – at least one first block [block (1)] complying with formula (I) as defined above; – at least one second block [block (2)] complying with formula (II) as defined above; – at least one third block [block (3)] complying with formula (IV) as defined above; and/or – optionally, at least one fourth block [block (4)] comprising a PFPE chain as defined above; with the proviso that * in copolymer (P _F-O-O ) – said block (1), said block (2), said block (3) and, when present, said at least one block (4) are statistically distributed, – the sum of (n+b) is at least 1, preferably from 1 to 15, more preferably from 1 to 11, even more preferably from 1 to 9; – the sum of (L+L^+e^+e*) is at least 1, preferably from 1 to 500, more preferably from 2 to 500, more preferably from 2 to 300; – the sum of (m+f) is at least 1, preferably from 1 to 100. SSPI 2022/021 [0084] Copolymer (P) and/or copolymer (P _F ) according to the present invention can be used for different applications in several industries, wherein outstanding resistance and durability at high temperature and harsh environments is required. For example, copolymer (P) and/or copolymer (PF) can be used as base oils as lubricants. Alternatively, copolymer (P) and/or copolymer (PF) can be used as additives in halogenated oils and/or greases. [0085] To this aim and advantageously, the copolymers according to the present invention as well as the mixtures described herein, are in the liquid state at room temperature, or even at temperatures lower than room temperature, with advantages in handling and storage of the copolymers. [0086] Hence, advantageously, copolymer (P) is in the liquid state at room temperature. [0087] Also, advantageously, copolymer (P _F ) is in the liquid state at room temperature. [0088] In addition, each of copolymer (PO-O) and copolymer (PF-O-O) as well as each of mixture (M1) and mixture (M2) is in the liquid state at room temperature. [0089] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence. [0090] The invention will be hereinafter illustrated in greater detail by means of the Examples contained in the following Experimental Section; the Examples are merely illustrative and are by no means to be interpreted as limiting the scope of the invention. Experimental section [0091] Materials [0092] Peroxidic perfluoropolyether oil was obtained by Solvay Specialty Polymers Italy S.p.A., complying with formula XO-(CF ₂ CF ₂ O) _a1 (CF ₂ O) _a2 (O) _h -X’ wherein X and X’ were -CF ₃ , -CF ₂ COF, -COF and having the following properties: Mn = 31990 g/mol; P.O.= 1.61%; a1/a2 = 1.0 [0093] The following were purchased by Anles LTD and used as such: (8CNVE) CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ CF ₂ CN (PBVE) CF2=CFOCF2CF2CF2OCF=CF2 [0094] Perfluorinated solvents Galden(R) HT200 and Galden(R) D100, as well as tetrafluoroethylene (TFE) and perfluoro-methylvinyl-ether (PMVE), and perfluorinated sulfonyl vinyl ether (VEFS) CF2=CFOCF2CF2SO2F were obtained by Solvay Specialty Polymers Italy S.p.A.. [0095] Methods: [0096] ¹⁹ F-NMR-Varian Mercury 300 MHz spectrometer working for the ¹⁹ F nucleus was used to obtain the structure, molecular weight, chain end composition of the perfluoropolyether oils. The ¹⁹ F-NMR spectrum was obtained on pure samples using CFCl ₃ as internal reference. [0097] The peroxidic content (PO) was expressed as grams of peroxidic oxygen per 100 g of polymer. The analysis of the peroxide content was carried out by iodometric titration using a Mettler DL40 device equipped with platinum electrode. The sensitivity limit for the PO determination was 0.0002%. [0098] GPC analyses were performed on a Waters GPC equipped with an RI detector and operating at 35°C. All average molecular weight results are reported compared to perfluoropolyethers linear neutral internal standards. [0099] The complex viscosity was measured by means of frequency sweep tests, using an MCR502 Anton-Paar rheometer with parallel plate geometry (25mm diameter). SSPI 2022/021 The viscosity was measured in this way at 25°C and 100°C and its value at 0.1 rad/s of oscillation is reported. [00100] Example 1 - PFPE copolymer with VEFS, TFE, PMVE and PBVE [00101] 250.3 g of the peroxidic perfluoropolyether oil described above were charged in a 1500 mL stirred cylindrical photochemical reactor equipped with a high pressure mercury lamp model HANAU TQ150, a thermocouple, a condenser and a mechanical stirrer. [00102] The oil was diluted with 1876 g of Galden(R) HT200 and then 23.0 g of VEFS and 1.1 g of PBVE were added to the reactor. [00103] The mixture was then purged with nitrogen under stirring, after which two fluorinated olefins, PMVE and TFE, were introduced into the reactor, at a rate of 14.6 and 8.0 g/h, respectively. After the flow started, the UV lamp was switched on and the reaction was conducted at 20°C for 7h. After this time the olefin flows were interrupted, the UV lamp was switched off. [00104] The obtained solution was distilled at 240°C for 4h in a round bottom flask equipped with a magnetic stirrer in order to remove the solvent and unreacted monomer traces. The distillation was conducted first at atmospheric pressure, then under reduced pressure (0.1 mbar) until complete removal of the solvent. [00105] 298.0 g of copolymer in the form of a clear viscous oil were obtained as residue, which was analysed by iodometric titration to confirm the complete removal of the peroxide units. [00106] ¹⁹ F-NMR analysis confirmed the absence of residual peroxide units. [00107] The incorporation of VEFS, TFE and MVE in the copolymer was at a concentration respectively of 5.3, 13.9 and 9.8 weight %. [00108] The copolymer had a1/a2 = 0.9 and X and X’= -CF3, -CF2COF and -OCOF. [00109] Example 2 – PFPE copolymers with 8CNVE, PBVE, TFE and PMVE [00110] 251.8 g of the peroxidic perfluoropolyether oil described above were charged in the same reactor as Example 1. The oil was diluted with 1873 g of Galden(R) D100. Next, 29.2 g of 8CNVE and 2.5 g of PBVE were added to the reactor. [00111] The mixture was then purged with nitrogen under stirring, after which two fluorinated olefins, PMVE and TFE, were introduced into the reactor, at a rate of 17.1 and 9.3 g/h, respectively. After the flow started, the UV lamp was switched on and the reaction was conducted at 20°C for 6h. After this time the olefin flows were interrupted and the UV lamp was kept on for further 35 hours at 20°C. [00112] After a total of 35 hours of UV irradiation, the lamp was switched off and the reaction mixture was transferred into a 2-L round bottom flask. The mixture was stripped at 120°C for 6h under reduced pressure (0.1 mbar) until complete removal of the solvent and unreacted monomer traces. [00113] 271.4 g of copolymer in the form of a clear viscous oil were obtained as residue. [00114] ¹⁹ F-NMR analysis confirmed the incorporation of 8CNVE, TFE and MVE in the copolymer at a concentration respectively of 7.0, 14.2 and 9.6 weight %. [00115] The copolymer had a1/a2 = 0.9 and X and X’= -CF ₃ , -CF ₂ COF and -OCOF. [00116] The introduction of the -CN functional groups was also confirmed by FT-IR spectroscopy measurements, confirming the presence of the peak at 2269 cm ^-1 . [00117] Comparative Example 1 - PFPE copolymers with VEFS, TFE and PMVE [00118] 251 g of the peroxidic perfluoropolyether oil described above were charged in a the same reactor as Example 1. The oil was diluted with 1876 g of a SSPI 2022/021 perfluorinated solvent, Galden(R) HT200, and 14.0 g of VEFS were added to the reactor. [00119] The mixture was then purged with nitrogen under stirring, after which two fluorinated olefins, PMVE and TFE, were introduced into the reactor, at a rate of 14.6 and 8.0 g/h, respectively. After the flow started, the UV lamp was switched on and the reaction was conducted at 20°C for 7h. After this time, the olefin flows were interrupted, the UV lamp was switched off [00120] The obtained solution was distilled at 240°C for 4h in a round bottom flask equipped with a magnetic stirrer in order to remove the solvent and unreacted monomer traces. The distillation was conducted first at atmospheric pressure, then under reduced pressure (0.1 mbar) until complete removal of the solvent. [00121] 275.1 g of copolymer in the form of a clear viscous oil were obtained as residue, which was analysed by iodometric titration to confirm the complete removal of the peroxide units. [00122] ¹⁹ F-NMR analysis confirmed the incorporation of VEFS, TFE and PMVE in the copolymer at a concentration respectively of 3.8, 13.4 and 9.6 weight % . [00123] The copolymer had Mn = 35600 g/mol, a1/a2 = 0.9 and X and X’= -CF ₃ , -CF ₂ COF and -OCOF. [00124] Comparative Example 2 - PFPE copolymers with 8CNVE, TFE and PMVE [00125] 250 g of the peroxidic perfluoropolyether oil described above were charged in the same reactor as Example 1. The oil was diluted with 1875 g of a perfluorinated solvent, Galden(R) D100, and 29.2 g of 8CNVE were added to the reactor. [00126] The mixture was then purged with nitrogen under stirring, after which two fluorinated olefins, PMVE and TFE, were introduced into the reactor, at a rate of 17.1 and 9.3 g/h, respectively. After the flow started, the UV lamp was switched on and the reaction was conducted at 20°C for 6h. After this time the olefin flows were interrupted and the UV lamp was kept on for further 35 hours at 20°C. [00127] After a total of 35 hours of UV irradiation, the lamp was switched off and the reaction mixture was transferred into a 2-L round bottom flask. The mixture was stripped at 120°C for 6h under reduced pressure (0.1 mbar) until complete removal of the solvent and unreacted monomer traces. [00128] 265 g of copolymer in the form of a clear viscous oil were obtained as residue. [00129] ¹⁹ F-NMR analysis of the product confirmed the incorporation of 8CNVE, TFE and PMVE in the copolymer at a concentration respectively of 7.3, 12.0 and 11.4 weight %. [00130] The copolymer had: Mn = 35000 g/mol, a1/a2 = 0.9, and X and X’= -CF3 , - CF2COF and -OCOF. [00131] The properties of the copolymers according to the invention and of comparison are summarised in Table 1 below. Table 1 SSPI 2022/021 (*) comparative n/p = not performed