In one embodiment, a method of making a crosslinked fluoropolymer is described. The method comprises applying a composition to a substrate, wherein the composition comprises fluoropolymer and a fluorinated solvent, one or more curing agents comprising an ethylenically unsaturated group and an electron donor group or precursor thereof. The method further comprises removing the solvent and curing the fluoropolymer with actinic (e.g. ultraviolet “UV”) radiation.

In another embodiment, a composition is described comprising a fluoropolymer dissolved in a fluorinated solvent, and one or more curing agents comprising an ethylenically unsaturated group and an electron donor group or precursor thereof. In each of these embodiments, the fluoropolymer comprises a sufficient amount (e.g. at least 90% by weight) of polymerized units derived from perfluorinated monomers such that the fluoropolymer dissolves in the fluorinated solvent. The fluoropolymer further comprises cure sites selected from iodine, bromine, and chlorine.

Also described are articles such as sheets or coated substrates comprising the crosslinked fluoropolymer composition described herein.

Detailed Description

Presently described are compositions comprising fluoropolymers dissolved in a fluorinated solvent, articles such as films and coated substrates, and methods of making a crosslinker fluoropolymer. The fluoropolymers described herein are copolymers that comprise predominantly, or exclusively, (e.g. repeating) polymerized units derived from two or more perfluorinated comonomers. Copolymer refers to a polymeric material resulting from the simultaneous polymerization of two or more monomers. In some embodiments, the comonomers include tetrafluoroethene (TFE) and one or more unsaturated perfluorinated (e.g. alkenyl, vinyl) alkyl ethers.

In some favored embodiments, the one or more unsaturated perfluorinated alkyl ethers are selected from the general formula:

R _f O-(CF ₂ ) _n -CF=CF ₂ wherein n is 1 (allyl ether) or 0 (vinyl ether) and R _f represents a perfluoroalkyl residue which may be interrupted once or more than once by an oxygen atom. R _f may contain up to 10 carbon atoms, e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 carbon atoms. Preferably R _f contains up to 8, more preferably up to 6 carbon atoms and most preferably 3 or 4 carbon atoms. In one embodiment R _f has 3 carbon atoms. In another embodiment R _f has 1 carbon atom. R _f may be linear or branched, and it may contain or not contain a cyclic unit. Specific examples of R _f include residues with one or more ether functions including but not limited to:

-(CF ₂ )-O-C ₃ F _7,

-(CF ₂ ) ₂ -O-C ₂ F _5,

-(CF ₂ ) _r3 -O-CF _3,

-(CF ₂ -O)-C ₃ F _7,

-(CF ₂ -O) ₂ -C ₂ F _5,

-(CF ₂ -O) ₃ -CF ₃ ,

-(CF ₂ CF ₂ -O)-C ₃ F _7,

-(CF ₂ CF ₂ -O) ₂ -C ₂ F _5,

-(CF ₂ CF ₂ -O) ₃ -CF _3,

Other specific examples for R _f include residues that do not contain an ether function and include but are not limited to -C ₄ F _9; -C ₃ F _7, -C ₂ F _5, -CF _3, wherein the C ₄ and C ₃ residues may be branched or linear, but preferably are linear.

Specific examples of suitable perfluorinated alkyl vinyl ethers (PAVE’s) and perfluorinated alkyl allyl ethers (PAAE’s) include but are not limited to perfluoro (methyl vinyl) ether (PMVE), perfluoro (ethyl vinyl) ether (PEVE), perfluoro (n-propyl vinyl) ether (PPVE-1), perfluoro-2-propoxypropylvinyl ether (PPVE-2), perfluoro-3-methoxy-n- propylvinyl ether, perfluoro-2-methoxy-ethylvinyl ether, CF ₂ =CF-O-CF ₂ -O-C ₂ F _5, CF ₂ =CF-O- CF ₂ -O-C ₃ F ₇ , CF ₃ -(CF ₂ ) ₂ -O-CF(CF ₃ )-CF ₂ -O-CF(CF ₃ )-CF ₂ -O-CF=CF ₂ and their allyl ether homologues. Specific examples of allyl ethers include CF ₂ =CF-CF ₂ -O-CF ₃ , CF ₂ =CF-CF ₂ -O- C ₃ F ₇ , CF ₂ =CF-CF ₂ -O-(CF ₃ ) ₃ -O-CF ₃ .

Further examples include but are not limited to the vinyl ether described in European patent application EP 1,997,795 Bl.

Perfluorinated ethers as described above are commercially available, for example from Anles Ltd., St. Petersburg, Russia and other companies or may be prepared according to methods described in U.S. Pat. No. 4,349,650 (Krespan) or European Patent 1,997,795, or by modifications thereof as known to a skilled person. In some embodiments, the one or more unsaturated perfluorinated alkyl ethers comprises unsaturated cyclic perfluorinated alkyl ethers, such as 2,2-bistrifluoromethyl-4,5- difluoro-1,3 dioxole. In other embodiments, the fluoropolymer is substantially free of unsaturated cyclic perfluorinated alkyl ethers, such as 2,2-bistrifluoromethyl-4,5-difluoro-1,3 dioxole. By substantially free it is meant that the amount is zero or sufficiently low such the fluoropolymer properties are about the same.

In some favored embodiments, the fluoropolymers are derived predominantly or exclusively from perfluorinated comonomers including tetrafluoroethene (TFE) and one or more of the unsaturated perfluorinated alkyl ethers described above. “Predominantly” as used herein means at least 90% by weight based on the total weight of the fluoropolymer, of the polymerized units of the fluoropolymer are derived from such perfluorinated comonomers such as tetrafluoroethene (TFE) and one or more unsaturated perfluorinated alkyl ethers. In some embodiments, the fluoropolymer comprises at least 91, 92, 93, 94, 95, 96, or 97% by weight or greater of such perfluorinated comonomers, based on the total weight of the fluoropolymer.

The fluoropolymers may contain at least 40, 45, or 50% by weight of polymerized units derived from TFE. In some embodiments, the maximum amount of polymerized units derived from TFE is no greater than 60% by weight.

The fluoropolymer typically comprises polymerized units derived from one or more of the unsaturated perfluorinated alkyl ethers (PAVE) (e.g. PMVE, PAAE or a combination thereof), in an amount of at least 10, 15, 20, 2.5, 30, 45, or 50% by weight, based on the total polymerized monomer units of the fluoropolymer. In some embodiments, the fluoropolymer comprises no greater than 50, 45, 40, or 35 % by weight of polymerized units derived from one or more of the unsaturated perfluorinated alkyl ethers (PMVE, PAAE or a combination thereof), based on the total polymerized monomer units of the fluoropolymer. The molar ratio of units derived from TFE to the perfluorinated alkly ethers described above may be, for example, from 1 : 1 to 5 : 1. In some embodiments, the molar ratio ranges from 1.5 : 1 to 3 : 1.

The fluoropolymers may be thermoplastic but, in a preferred embodiment, the fluoropolymer is amorphous. As used herein, amorphous fluoropolymers are materials that contain essentially no crystallinity or possess no significant melting point (peak maximum) as determined by differential scanning calorimetry in accordance with DIN EN ISO 11357- 3:2013-04 under nitrogen flow and a heating rate of 10°C/min. Typically, amorphous fluoropolymers have a glass transition temperature (Tg) of less than 26°C, less than 20°C, or less than 0°C, and for example from - 40°C to 20°C, or -50°C to 15°C, or -55°C to 10°C. The fluoropolymers may typically have a Mooney viscosity (ML 1+10 at 121 °C) of from about 2 to about 150, for example from 10 to 100, or from 20 to 70. For amorphous polymers containing cyclic perfluorinated alky ether units, the glass transition temperature is typically at least 70°C, 80°C, or 90°C, and may range up to 220°C, 250°C, 270°C, or 290°C. The MFI (297 °C/5 kg) is between 0.1 - 1000 g/10 min.

In other embodiments, the fluoropolymer may have a melt point of less than 150°C or

100°C.

The fluoropolymer is preferably a curable fluoropolymer that contains one or more cure sites. Cure sites are functional groups that react in the presence of a curing agent or a curing system to cross-link the polymers. The cure sites are typically introduced by copolymerizing cure -site monomers, which are functional comonomers already containing the cure sites or precursors thereof. One indication of crosslinking is that the dried and cured coating composition was not soluble in the fluorinated solvent of the coating.

The cure sites may be introduced into the polymer by using cure site monomers, i.e. functional monomers as will be described below, functional chain-transfer agents and starter molecules. The fluoroelastomers may contain cure sites that are reactive to more than one class of curing agents.

The curable fluoroelastomers may also contain cure sites in the backbone, as pendent groups, or cure sites at a terminal position. Cure sites within the fluoropolymer backbone can be introduced by using a suitable cure-site monomer. Cure site monomers are monomers containing one or more functional groups that can act as cure sites or contain a precursor that can be converted into a cure site.

In some embodiments, the cure sites comprise iodine or bromine atoms.

Iodine-containing cure site end groups can be introduced by using an iodine-containing chain transfer agent in the polymerization. Iodine-containing chain transfer agents will be described below in greater detail. Halogenated redox systems as described below may be used to introduce iodine end groups.

In addition to iodine cures sites, other cure sites may also be present, for example Br- containing cure sites or cure sites containing one or more nitrile groups. Br-containing cure sites may be introduced by Br-containing cure-site monomers.

Examples of cure-site comonomers include for instance:

(a) bromo- or iodo- (per)fluoroalkyl-(per)fluorovinylethers, for example including those having the formula:

ZRf-O-CX=CX ₂ wherein each X may be the same or different and represents H or F, Z is Br or I, Rf is a C1-C12 (per)fluoroalkylene, optionally containing chlorine and/or ether oxygen atoms. Suitable examples include ZCF ₂ -O-CF=CF ₂ , ZCF ₂ CF ₂ -O-CF=CF ₂ , ZCF ₂ CF ₂ CF ₂ -O-CF=CF ₂ , CF ₃ CFZCF ₂ -O-CF=CF ₂ or ZCF ₂ CF _2- 0-CF ₂ CF ₂ CF ₂ -O-CF=CF ₂ wherein Z represents Br of I; and

(b) bromo- or iodo perfluoroolefms such as those having the formula:

Z'-(Rf)r-CX=CX ₂ wherein each X independently represents H or F, Z' is Br or I, Rf is a C ₁ -C ₁₂ perfluoroalkylene, optionally containing chlorine atoms and r is 0 or 1; and

(c) non-fluorinated bromo and iodo-olefms such as vinyl bromide, vinyl iodide, 4-bromo- 1- butene and 4-iodo-l -butene.

Specific examples include but are not limited to compounds according to (b) wherein X is H, for example compounds with X being H and Rf being a C1 to C3 perfluoroalkylene. Particular examples include: bromo- or iodo-trifluoroethene, 4-bromo-perfluorobutene-1, 4- iodo-perfluorobutene-1, or bromo- or iodo-fluoroolefms such as 1-iodo,2,2-difluroroethene, 1- bromo-2,2-difluoroethene, 4-iodo-3,3,4,4,-tetrafluorobutene-1 and 4-bromo-3, 3,4,4- tetrafluorobutene-1; 6-iodo-3,3,4,4,5,5,6,6-octafluorohexene-1.

In some embodiments, the cure sites comprise chlorine atoms. Such cure-site monomers include those of the general formula: CX ₁ X ₂ =CY ₁ Y ₂ where X ₁ , X ₂ are independently H and F; Y ₁ is H, F, or Cl; and Y ₂ is Cl, a fluoroalkyl group (RF) with at least one Cl substiuent, a fluoroether group (ORF) with at least one Cl substituent, or -CF ₂ -ORF. The fluoroalkyl group (RF) is typically a partially or fully fluorinated C ₁ -C ₅ alkyl group. Examples of cure-site monomer with chlorine atoms include CF ₂ =CFC1, CF ₂ =CF-CF ₂ C1, CF ₂ =CF-O- (CF ₂ ) _n -Cl, n = 1-4; CH ₂ =CHCI, CH ₂ =CCI ₂ .

Typically, the amount of iodine or bromine or chlorine or their combination in the fluoropolymer is between 0.001 and 5%, preferably between 0.01 and 2.5%, or 0.1 to 1 % or 0.2 to 0.6% by weight with respect to the total weight of the fluoropolymer. In one embodiment the curable fluoropolymers contain between 0.001 and 5 %, preferably between 0.01 and 2.5 %, or 0.1 to 1 %, more preferably between 0.2 to 0.6 % by weight of iodine based on the total weight of the fluoropolymer. The composition may optionally further comprise a second fiuoropolymer that lacks halogen cure sites. The amount of fiuoropolymer lacking halogen cure sites is typically less than 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5 wt.% of the total fiuoropolymer. Thus, the composition has a sufficient amount of fiuoropolymer with halogen cure sites such that adequate crosslinking is achieved.

In one embodiments, the composition further comprises a second fiuoropolymer derived predominantly, or exclusively from two or more perfluorinated comonomers including tetrafluoroethene (TFE) and one or more unsaturated cyclic perfluorinated alkyl ethers, such as 2,2-bistrifluoromethyl-4,5-difluoro-1,3 dioxole. Such fluoropolymers are commercially available as “TEFLON™ AF”, “CYTOP™”, and “HYFLON™”.

In some embodiments, the second fiuoropolymer contains nitrile-containing cure sites. When a combination of fluoropolymers with different cure site is utilized the composition may be characterized as a dual curing, containing different cure sites that are reactive to different curing systems.

Fluoropolymers with nitrile-containing cure sites are known, such as described in U.S. Patent No. 6,720,360.

Nitrile-containing cure sites may be reactive to other cure systems for example, but not limited to, bisphenol curing systems, peroxide curing systems, triazine curing systems, and especially amine curing systems. Examples of nitrile containing cure site monomers correspond to the following formulae:

CF ₂ =CF-CF ₂ -O-Rf-CN;

CF ₂ =CFO(CF ₂ ) _r CN;

CF ₂ =CFO[CF ₂ CF(CF ₃ )O] _p (CF ₂ ) _v OCF(CF ₃ )CN;

CF ₂ =CF[OCF ₂ CF(CF ₃ )] _k O(CF ₂ ) _u CN; wherein, r represents an integer of 2 to 12; p represents an integer of 0 to 4; k represents 1 or 2; v represents an integer of 0 to 6; u represents an integer of 1 to 6, Rf is a perfluoroalkylene or a bivalent perfluoroether group. Specific examples of nitrile containing fluorinated monomers include but are not limited to perfluoro (8-cyano-5-methyl-3,6-dioxa-1-octene), CF ₂ =CFO(CF ₂ ) ₅ CN, and CF ₂ =CFO(CF ₂ ) ₃ OCF(CF ₃ )CN.

In some embodiments, the amount of nitrile-containing cure site comonomer is typically at least 0.5, 1, 1.5, 2, 2.5, 3. 3.5, 4, 4.5 or 5% by weight and typically no greater than 10% by weight; based on the total weight of the fluoropolymer. Suitable curing agents for nitrile cure sites are known in the art and include, but are not limited to amidines, amidoximes and others described in W02008/094758 Al, incorporated herein by reference.

In other embodiments, the composition is substantially free of fluoropolymer with nitrile-containing cure sites.

In other embodiments, halogenated chain transfer agents can be utilized to provide terminal cure sites. Chain transfer agents are compounds capable of reacting with the propagating polymer chain and terminating the chain propagation. Examples of chain transfer agents reported for the production of fluoroelastomers include those having the formula RI _X , wherein R is an x-valent fluoroalkyl or fluoroalkylene radical having from 1 to 12 carbon atoms, which, may be interrupted by one or more ether oxygens and may also contain chlorine and/or bromine atoms. R may be Rf and Rf may be an x-valent (per)fluoroalkyl or (per)fluoroalkylene radical that may be interrupted once or more than once by an ether oxygen. Examples include alpha-omega diiodo alkanes, alpha-omega diiodo fluoroalkanes, and alpha- omega diiodoperfluoroalkanes, which may contain one or more catenary ether oxygens. “Alpha-omega” denotes that the iodine atoms are at the terminal positions of the molecules. Such compounds may be represented by the general formula X-R-Y with X and Y being I and R being as described above. Specific examples include di-iodomethane, alpha-omega (or 1,4-) diiodobutane, alpha-omega (or 1,3-) diiodopropane, alpha-omega (or 1,5-) diiodopentane, alpha-omega (or 1,6-) diiodohexane and 1,2-diiodoperfluoroethane. Other examples include fluorinated di-iodo ether compounds of the following formula:

R _f -CF(I)- (CX ₂ )„-(CX ₂ CXR) _m -O-R”f-O _k -(CXR’CX ₂ ) _p -(CX ₂ ) _q -CF(I)-R' _f wherein X is independently selected from F, H, and Cl; R _f and R’ _f are independently selected from F and a monovalent perfluoroalkane having 1-3 carbons; R is F, or a partially fluorinated or perfluorinated alkane comprising 1-3 carbons; R” _f is a divalent fluoroalkylene having 1-5 carbons or a divalent fluorinated alkylene ether having 1-8 carbons and at least one ether linkage; k is 0 or 1; and n, m, and p are independently selected from an integer from 0-5, wherein, n plus m at least 1 and p plus q are at least 1.

The fluoropolymers may or may not contain units derived from at least one modifying monomer. The modifying monomers may introduce branching sites into the polymer architecture. Typically, the modifying monomers are bisolefms, bisolefmic ethers or polyethers. The bisolefms and bisolefmic (poly)ethers may be perfluorinated, partially fluorinated or non-fluorinated. Preferably they are perfluorinated. Suitable perfluorinated bisolefmic ethers include those represented by the general formula: CF ₂ =CF-(CF ₂ )n-O-(Rf)-O-(CF ₂ ) _m -CF=CF ₂ wherein n and m are independent from each other either 1 or 0 and wherein Rf represents a perfluorinated linear or branched, cyclic or acyclic aliphatic or aromatic hydrocarbon residue that may be interrupted by one or more oxygen atoms and comprising up to 30 carbon atoms. A particular suitable perfluorinated bisolefmic ether is a di-vinylether represented by the formula:

CF ₂ =CF-O-(CF ₂ )n-O-CF=CF ₂ wherein n is an integer between 1 and 10, preferably 2 to 6., e.g. n may be 1, 2, 3, 4, 5, 6 or 7. More preferably, n represents an uneven integer, for example 1, 3, 5 or 7.

Further specific examples include bisolefmic ethers according the general formula

CF ₂ =CF-(CF ₂ )„-O-(CF ₂ )p-O-(CF ₂ ) _m -CF=CF ₂ wherein n and m are independently either 1 or 0 and p is an integer from 1 to 10 or 2 to 6. For example, n may be selected to represent 1, 2, 3, 4, 5, 6 or 7, preferably, 1, 3, 5 or 7.

Further suitable perfluorinated bisolefmic ethers can be represented by the formula

CF ₂ =CF-(CF ₂ )p-O-(R _af O) _n (R _bf O) _m -(CF ₂ ) _q -CF=CF ₂ wherein R _af and R _bf are different linear or branched perfluoroalkylene groups of 1 - 10 carbon atoms, in particular, 2 to 6 carbon atoms, and which may or may not be interrupted by one or more oxygen atoms. R _af and/or R _bf may also be perfluorinated phenyl or substituted phenyl groups; n is an integer between 1 and 10 and m is an integer between 0 and 10, preferably m is 0. Further, p and q are independently 1 or 0.

In another embodiment, the perfluorinated bisolefmic ethers can be represented by the formula just described wherein m, n, and p are zero and q is 1-4.

Modifying monomers can be prepared by methods known in the art and are commercially available, for example, from Anles Ltd., St. Petersburg, Russia.

Preferably, the modifiers are not used or only used in low amounts. Typical amounts include from 0 to 5 %, or from 0 to 1.4 % by weight based on the total weight of the fluoropolymer. Modifiers may be present, for example, in amounts from about 0.1 % to about 1.2 % or from about 0.3 % to about 0.8 % by weight based on the total weight of fluoropolymer. Combinations of modifiers may also be used.

The fluoropolymers may contain partially fluorinated or non-fluorinated comonomers and combinations thereof, although this is not preferred. Typical partially fluorinated comonomers include but are not limited to 1,1-dif uoroethene (vinylidenefluoride, VDF) and vinyl fluoride (VF) or trifluorochloroethene or trichlorofluoroethene. Examples of non- fluorinated comonomers include but are not limited to ethene and propene. The amount of units derived from these comonomers include from 0 to 8% by weight based on the total weight of the fluoropolymer. In some embodiments, the concentration of such comonomer is no greater than 7, 6, 5, 4, 3, 2, or 1% by weight based on the total weight of the fluoropolymer.

In a preferred embodiment, the curable fluoropolymer is a perfluoroelastomer that comprises repeating units (exclusivel)y derived from the perfluorinated comonomers but may contain units derived from cure-site monomers, and modifying monomers if desired. The cure- site monomers and modifying monomers may be partially fluorinated, not fluorinated or perfluorinated, and preferably are perfluorinated. The perfluoroelastomers may contain from 69 to 73, 74, or 75% fluorine by weight (based on the total amount of perfluoroelastomer). The fluorine content may be achieved by selecting the comonomers and their amounts accordingly.

Such highly-fluorinated amorphous fluoropolymers typically do not dissolve to the extent of at least 1 wt. %, at room temperature and standard pressure, in a hydrogen-containing organic liquid (e.g., it does not dissolve in any of methyl ethyl ketone (“MEK”), tetrahydrofuran (“THF”), ethyl acetate or N-methyl pyrrolidinone (“NMP”)).

The fluoropolymers can be prepared by methods known in the art, such as bulk, suspension, solution or aqueous emulsion polymerization. For example, the polymerisation process can be carried out by free radical polymerization of the monomers alone or as solutions, emulsions, or dispersions in an organic solvent or water. Seeded polymerizations may or may not be used. Curable fluoroelastomers that can be used also include commercially available fluoroelastomers, in particular perfluoroelastomers.

The fluoropolymers may have a monomodal or bi-modal or multi-modal weight distribution. The fluoropolymers may or may not have a core-shell structure. Core-shell polymers are polymers where towards the end of the polymerization, typically after at least 50 % by mole of the comonomers are consumed, the comonomer composition or the ratio of the comonomers or the reaction speed is altered to create a shell of different composition.

The fluoropolymer compositions described herein contain one or more ethylenically unsaturated curing agents. The ethylenically unsaturated curing agents are typically present in an amount of at least 1, 1.5, or 2 wt.% based on the total weight of the fluoropolymer. For compositions having a lower amount of crosslinking, the ethylenically unsaturated curing agents may be present at a lower amount such as at least 0.005, 0.1, 0.2, 0.3, 0.5 wt.%. The maximum amount of ethylenically unsaturated curing agents is typically no greater than 10, 9,

8, 7, 6, or 5 wt.% based on the total weight of the fluoropolymer.

The ethylenically unsaturated group(s) of the curing agent are typically (meth)acryl including (meth)acrylate RCH=CHCOO- and (meth)acrylamide RCH=CHCONH-, wherein R is methyl of hydrogen; alkenyl including vinyl (CH ₂ =CH-); or alkynyl.

Useful multi- (meth)acrylate curing agents include

(a) di(meth)acryl containing monomers such as 1,3 -butylene glycol diacrylate, 1,4- butanediol diacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol monoacrylate monomethacrylate, ethylene glycol diacrylate, alkoxylated aliphatic diacrylate, alkoxylated cyclohexane dimethanol diacrylate, alkoxylated hexanediol diacrylate, alkoxylated neopentyl glycol diacrylate, caprolactone modified neopentylglycol hydroxypivalate diacrylate, caprolactone modified neopentylglycol hydroxypivalate diacrylate, cyclohexanedimethanol diacrylate, diethylene glycol diacrylate, dipropylene glycol diacrylate, ethoxylated bisphenol A diacrylate, hydroxypivalaldehyde modified trimethylolpropane diacrylate, neopentyl glycol diacrylate, polyethylene glycol diacrylate, propoxylated neopentyl glycol diacrylate, tetraethylene glycol diacrylate, tricyclodecanedimethanol diacrylate, triethylene glycol diacrylate, tripropylene glycol diacrylate;

(b) tri(meth)acryl containing monomers such as glycerol triacrylate, trimethylolpropane triacrylate, ethoxylated triacrylates (e.g., ethoxylated trimethylolpropane triacrylate), propoxylated triacrylates (e.g., propoxylated glyceryl triacrylate, propoxylated trimethylolpropane triacrylate), trimethylolpropane triacrylate, tris(2- hydroxyethyl)isocyanurate triacrylate;

(c) higher functionality (meth)acryl containin monomer such as ditrimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate, pentaerythritol triacrylate, ethoxylated pentaerythritol tetraacrylate, and caprolactone modified dipentaerythritol hexaacrylate.

In some embodiments, the ethylenically unsaturated curing agent comprises at least two or three ethylenically unsaturated groups. The maximum number of ethylenically unsaturated groups is typically 3, 4, 5, or 6. In this embodiment, the ethylenically unsaturated groups are preferably alkenyl groups. Thus, the composition in some embodiments, the composition is substantially free of (meth)acrylate groups.

The ethylenically unsaturated curing agent may be linear, branched, or comprise a cyclic group. The ethylenically unsaturated curing agent may be aliphatic or aromatic. Examples of useful ethylenically unsaturated curing agents include triallyl cyanurate; triallyl isocyanurate; triallyl trimellitate; tri(methylallyl)isocyanurate; tris(diallylamine)-s- triazine; triallyl phosphite; (N,N’)-diallyl acrylamide; hexaallyl phosphoramide; (N,N,N,N)- tetraalkyl tetraphthalamide; (N,N,N',N-tetraallylmalonamide; trivinyl isocyanurate; N,N'-m- phenylenebismaleimide; diallyl-phthalate andtri(5-norbomene-2-methylene)cyanurate. In some embodiments, the ethylenically unsaturated curing agent is heterocyclic such as in the case of triallyl isocyanurate (TAIC).

In some embodiments, the ethylenically unsaturated curing agent comprises a silicone- containing moiety such as silane or siloxane. When the curing agent includes silicone- containing moiety, the curing agent can also promote adhesion of the fluoropolymer to a substrate.

Suitable ethylenically unsaturated curing agent that comprise silicone-containing moieties include for example diallydimethylsilane; and 1,3-divinyltetramethyl disiloxane.

In some embodiment, the ethylenically unsaturated curing agent comprises at least one ethylenically unsaturated group and at least one alkoxy silane group. Suitable curing agents include for example (meth)acryloy alkoxy silanes such as 3-

(methacryloxy)propyltrimethoxysilane, 3-(methacryloxy)propylmethyldimethoxysilane, 3- (acryloyloxypropyl)methyl dimethoxy silane, 3-

(methacryloyloxy)propyldimethylmethoxysilane, and 3 -(acryloxypropyl) dimethylmethoxy silane. In some embodiments, the amount of (meth)acryloy alkoxy silanes is at least 2, 3, 4, or 5 wt.% to achieve a highly crosslinked fluoropolymer.

Suitable alkenyl alkoxy silanes include vinyldimethylethoxysilane, vinylmethyldiacetoxysilane, vinylmethyldiethoxysilane, vinyltriacetoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinyltrimethoxysilane, vinyltriphenoxy silane, vinyltri-t-butoxysilane, vinyltris-isobutoxysilane, vinyltriisopropenoxysilane, vinyltris(2- methoxyethoxy)silane, and allyltriethoxysilane.

In some embodiments, the ethylenically unsaturated curing agent may have the general formula

X ¹ -L ¹ -SiR _m (OR ¹ ) _3-m ; wherein X ¹ is an ethylenically unsaturated group, such as (meth)acryl or vinyl;

L ¹ is an organic divalent linking group having 1 to 12 carbon atoms;

R is independently C ₁ -C ₄ alkyl and most typically methyl or ethyl;

R ¹ is independently H or C ₁ -C ₄ alkyl and most typically methyl or ethyl; and m ranges from 0 to 2. In typical embodiments, L ¹ is an alkylene group. In some embodiments, L ¹ is an alkylene group having 1, 2 or 3 carbon atoms. In other embodiments, L ¹ comprises or consists of an aromatic group such as phenyl or (e.g. C ₁ -C ₄ ) alkyl phenyl.

The composition may comprise a single ethylenically unsaturated curing agent as just described or combinations of ethylenically unsaturated curing agents.

The composition described herein further comprises an electron donor group or precursor thereof. The electron donor group may be present on the same compound such as in the case of an aminoalkene or vinylaniline or the electron donor group may be present as a separate compound.

The fluoropolymer and/or the curing agent(s) comprise a chromophore, i.e. an atom or group that absorbs light at a specified frequency. In some embodiments, the fluororpolymer and/or curing agent may not have sufficient absorbance independently, but have sufficient absorbance in combination with each other.

In some embodiments, the fluoropolymer, curing agent(s), or combination, thereof have an absorbance of at least 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1.0 at wavelength ranging from 190 nm to 400 nm. In some embodiments, such absorbance is at wavlength of at least 200 nm, 210 nm, 220 nm, 230 nm or 240 nm. In some embodiments, such absorbance is at wavlength of no greater than 350, 340, 330, 320, 310 nm, or 290 nm. In other embodiments, the fluoropolymer, curing agent(s), or combination, thereof have an absorbance of at least 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1.0 at wavelength ranging from 150 nm to 200 nm.

Without intending to be bound by theory, it is surmised that upon exposure to suitable wavelengths and intensities of actinic (e.g. UV) radiation the halogen atoms of the cure sites of the fluoropolymer become excited and ionize. The ionized halogen atoms react with the electron donor group rendering protonated cure sites in place of the former halogen atoms.

Such protonated cure site covalently bond with the ethylenically unsaturated group(s) of the curing agent.

Although other electon donor groups could be utilized, the compound comprising an electron donor group is typically an amine, or precursor thereof. Suitable amines include primary amine, secondary amines, teritiary amines, and combinations thereof. The amine may be aliphatic or aromatic.

Illustrative amine compounds include diamino hexane, N,N,N’,N’-tetramethyl-l,4- diamino butane (TMDAB); N,N-dimethyl aniline; triethylenetetramine; and diethylenetriamine. In some embodiments, the amine groups are spaced apart by an alkylene group having at least 3, 4, 5, or 6 (e.g. carbons) atoms. Typically, the number of (e.g. carbon) atoms is no greater than 12. When the amine compound has an insufficient chain length, it can be a less effective electon donor group. The alkylene group can optionally comprise subsituents, such as siloxane, provided the compound is an electron donor or precursor thereof.

In some embodiments, the electron donor compound may be characterized as an electron donor precursor meaning that when the compound is initially combined with the fluoropolymer it is not an electron donor. However, the precursor compound decomposes or otherwise reacts to form an (e.g. amine) electron donor prior to or during curing.

Electron donor precursors include nitrogen-containing nucleophilic compounds such as heterocyclic secondary amines; guanidines; compounds which decompose in-situ at a temperature between 40°C and 330°C to produce a guanidine; compounds which decompose in-situ at a temperature between 40°C and 330°C to produce a primary or secondary amine; nucleophilic compounds of the formula R ₁ -NH-R _2, wherein R ₁ is H-, a C ₁ -C ₁₀ aliphatic hydrocarbon group, or an and group having hydrogen atoms in the alpha positions, R ₂ is a C _1- C ₁₀ aliphatic hydrocarbon group, an aryl group having hydrogen atoms in the alpha positions, - CONHR ₃ , -NHCO ₂ R ₃ , or -OH ', and R ₃ is a C ₁ -C ₁₀ aliphatic hydrocarbon group; and substituted amidines of the formula HN=CR ₄ NR ₅ R _6, whereinR ₄ , R ₅ , R ₆ are independently H-, alkyl or aryl groups and wherein at least one of R ₄ , R ₅ and R ₆ is not H-.

As used herein, "heterocyclic secondary amine" refers to aromatic or aliphatic cyclic compound having at least one secondary amine nitrogen contained within the ring. Such compounds include, for example, pyrrole, imidazole, pyrazole, 3-pyrroline, and pyrrolidine.

Guanidines are compounds derived from guanidine, i.e. compounds which contain the radical, -NHCNHNH-, such as, but not limited to, diphenylguanidine, diphenylguanidine acetate, aminobutylguanidine, biguanidine, isopentylguanidine, di-o-tolylguanidine, o- tolylbiguanide, and triphenylguanidine.

Other compounds that decompose in-situ at a temperature between 40°C and 330°C to produce either a primary or secondary amine include, but are not limited to, di- or poly- substituted ureas (e.g. 1, 3-dimethyl urea); N-alkyl or -dialkyl carbamates (e.g. N-(tert- butyloxycarbonyl)propylamine); di- or poly-substituted thioureas (e.g. 1,3-dimethyl-thiourea); aldehyde-amine condensation products (e.g. 1,3,5-trimethylhexahydro-1,3,5-triazine); Ν,Ν'- dialkyl phthalamide derivatives (e.g. Ν,Ν'-dimethylphthalamide); and amino acids.

When thermally activated electron donor precursor compounds are utilized as just described, the composition is typically heated prior to and/or during curing.

Other types of amine electron donor include bis(aminophenols) and bis(aminothiophenols) of the formulas

and tetraamines of the formula where A is SO ₂ , O, CO, alkyl of 1-6 carbon atoms, perfluoroalkyi of 1-10 carbon atoms, or a carbon-carbon bond linking the two aromatic rings. The amino and hydroxyl groups in the above formulas are interchangeably in the meta and para positions with respect to group A.

In some embodiments, the amine electron donor compound is an aziridine compound.

In some embodiments, the aziridine compound comprises at least two aziridine groups. The aziridine compound may comprise 3, 4, 5, 6, or greater than 6 aziridine groups. The aziridine compound may be represented by the following structure: wherein R is a core moiety having a valency of Y;

L is a bond, divalent atom, or divalent linking group; R ₁ , R ₂ , R ₃ , and R ₄ are independently hydrogen or a C ₁ -C ₄ alkyl (e.g. methyl); and Y is typically 2, 3, or greater.

In some embodiments, R is -SO ₂ -. In some embodiments, R-L is a residue of a multi(meth)acrylate compound. In some embodiments L is a C ₁ -C ₄ alkylene, optionally substituted with one or more (e.g. contiguous or pendant) oxygen atoms thereby forming ether or ester linkages. In typical embodiments, R ₁ is methyl and R ₂ , R ₃ , and R ₄ are hydrogen.

Representative aziridine compounds include trimethylolpropane tri-[beta-(N- aziridinyl)-propionate, 2,2-bishydroxymethyl butanoltris [3 -(1 -aziridine) propionate]; 1- (aziridin-2-yl)-2-oxabut-3-ene; and 4-(aziridin-2-yl)-but-1-ene; and 5-(aziridin-2-yl)-pent-1- ene.

In some embodiments, a polyaziridine compound can be prepared by reacting divinyl sulfone with alkylene (e.g. ethylene) imine, such as described in US 3,235,544 (Christena). On representative compound is di(2-propyleniminoethyl)sulfone, as depicted as follows:

The above described polyaziridine compounds comprise at least two aziridine groups at the time the compound is added to the coating composition. In other embodiments, the polyaziridine compound does not comprise two aziridine groups at the time the compound is added to the composition, yet forms a polyaziridine in-situ. For example, compounds comprising a single aziridine group and a single (meth)acrylate group can form a dimer or oligomerize by reaction of the (meth)acrylate groups thereby forming a polyazirdine (i.e. diaziridine) compound.

In some embodiments, the composition comprises an electron donor compound comprising at least one (e.g. primary, secondary tertiary) amine group and at least one organosilane (e.g. alkoxy silane) group. Such compounds can improve bonding an independently crosslink the fluoroelastomers described herein, thereby providing a second fluoropolymer crosslinking mechanism. By use of ethylenically unsaturated curing agents in combination with amino-substituted organosilanes, highly crosslinked fluoropolymers can be provided utilizing lower concentrations of curing agents and electron donor compounds.

In some embodiments, the amine may be characterized as an amino-substituted organosilane ester or ester equivalent that bear on the silicon atom at least one, and preferably 2 or 3 ester or ester equivalent groups. Ester equivalents are known to those skilled in the art and include compounds such as silane amides (RNR'Si), silane alkanoates (RC(O)OSi), Si-O-Si, SiN(R)-Si, SiSR and RCONR'Si compounds that are thermally and/or catalytically displaceable by R”OH. R and R are independently chosen and can include hydrogen, alkyl, arylalkyl, alkenyl, alkynyl, cycloalkyl, and substituted analogs such as alkoxyalkyl, aminoalkyl, and alkylaminoalkyl. R" may be the same as R and R, except it may not be H. These ester equivalents may also be cyclic such as those derived from ethylene glycol, ethanolamine, ethylenediamine (e.g. N-[3-(trimethoxylsilyl)propyl] ethylenediamine) and their amides.

Another such cyclic example of an ester equivalent is

In this cyclic example R' is as defined in the preceding sentence, except that it may not be aryl. 3-aminopropyl alkoxysilanes are well known to cyclize upon heating, and these RNHSi compounds would be useful in this invention. Preferably the amino-substituted organosilane ester or ester equivalent has ester groups such as methoxy that are easily volatilized as methanol. The amino-substituted organosilane must have at least one ester equivalent; for example, it may be a trialkoxy silane.

For example, the amino-substituted organosilane may have the formula

(Z ₂ N-L-SiX'X"X'"), wherein

Z is hydrogen, alkyl, or substituted aryl or alkyl including amino-substituted alkyl; and L is a divalent straight chain C1-12 alkylene or may comprise a C3-8 cycloalkylene, 3-8 membered ring heterocycloalkylene, C2-12 alkenylene, C4-8 cycloalkenylene, 3-8 membered ring heterocycloalkenylene or heteroarylene unit; and each of X', X" and X'" is a C1-18 alkyl, halogen, C1-8 alkoxy, C1-8 alkylcarbonyloxy, or amino group, with the proviso that at least one of X', X", and X'" is a labile group. Further, any two or all of X', X" and X'" may be joined through a covalent bond. The amino group may be an alkylamino group.

L may be divalent aromatic or may be interrupted by one or more divalent aromatic groups or heteroatomic groups. The aromatic group may include a heteroaromatic. The heteroatom is preferably nitrogen, sulfur or oxygen. L is optionally substituted with C1-4 alkyl, C2-4 alkenyl, C2-4 alkynyl, C1-4 alkoxy, amino, C3-6 cycloalkyl, 3-6 membered heterocycloalkyl, monocyclic aryl, 5-6 membered ring heteroaryl, C1-4 alkylcarbonyloxy, C1-4 alkyloxycarbonyl, C1-4 alkylcarbonyl, formyl, C1-4 alkylcarbonylamino, or C1-4 aminocarbonyl. L is further optionally interrupted by -O-, -S-, -N(Rc)-, -N(Rc)-C(O)-, -N(Rc)- C(O)-O-, -O-C(O)-N(Rc)-, -N(Rc)-C(O)-N(Rd)-, -O-C(O)-, -C(O)-O-, or -O-C(O)-O-. Each of Rc and Rd, independently, is hydrogen, alkyl, alkenyl, alkynyl, alkoxyalkyl, aminoalkyl (primary, secondary or tertiary), or haloalkyl.

Examples of amino-substituted organosilanes include 3 -aminopropyltrimethoxy silane (SILQUEST A-1110), 3 -aminopropyltriethoxy silane (SILQUEST A-1100), bis(3- trimethoxysilylpropy)amine, bis(3-triethoxysilylpropy)amine, bis(3-trimethoxysilylpropy)n- methylamine, 3-(2-aminoethyl)aminopropyltrimethoxysilane (SILQUEST A-1120),

SILQUEST A-1130, (aminoethylaminomethyl)phenethyltrimethoxysilane, (aminoethylaminomethyl)- phenethyltriethoxysilane, N-(2-aminoethyl)-3- aminopropylmethyldimethoxysilane (SILQUEST A-2120), bis-(.gamma.- triethoxysilylpropyl)amine (SILQUEST A-1170), N-(2-aminoethyl)-3- aminopropyltributoxy silane, 6-(aminohexylaminopropyl)trimethoxysilane, 4- aminobutyltrimethoxysilane, 4-aminobutyltriethoxysilane, p-(2- aminoethyl)phenyltrimethoxysilane, 3-aminopropyltris(methoxyethoxyethoxy)silane, 3- aminopropylmethyldiethoxy- silane, oligomeric aminosilanes such as DYNASYLAN 1146, 3- (N-methylamino)propyltrimethoxy silane, N-(2-aminoethyl)-3- aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3- aminopropyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, 3- aminopropylmethyldimethoxy silane, 3 -aminopropyldimethylmethoxy silane , 3 - aminopropyldimethylethoxy silane, and the following cyclic compounds: A bis-silyl urea [RO) ₃ Si(CH ₂ )NR] ₂ C=O is another example of an amino-substituted organosilane ester or ester equivalent.

In some embodiments, the curing agent may comprise an amino group having latent functionality. One example of such curing agent is a blocked amine group, such as

R ³ — N=C(R ¹ )(R ² ) wherein R ¹ and R ² are independently selected from a linear or branched alkyl group comprising 1 to 6 carbon atoms. In typical embodiments R1 is methyl, and R ² a linear or branched alkyl group comprising at least 2, 3, 4, 5, or 6 carbon atoms. R ³ is typically an organic group (e.g. having a molecular weight less than 500, 450, 400, 350, 300, or 250 g/mole).

The blocked amine can be activated by moisture provided by water adsorbed on the surface of the substrate being coated or from humidity. Deblocking begins in minutes and is generally complete within a few (e.g. two) hours. During deblocking the — N=C(R ¹ )(R ² ) group is converted to -NH ₂ that can then react with the (e.g. nitrile cure sites) of the fluoropolymer.

In some embodiments, the curing agent comprises a blocked amine group and an alkoxy silane group. Such blocked amine curing agent can be characterized by the following general formula:

(R ⁴ O) _3— Si— (CH ₂ ) _m— N=C(R1)(R2) wherein R ¹ and R ² are independently selected from a linear or branched alkyl group comprising 1 to 6 carbon atoms as previously described

R ¹ is independently selected from a linear or branched alkyl group comprising 1 to 6 carbon atoms, m is an integer from 1 to 4, and each R ⁴ is independently a C1 or C2 alkyl group.

One illustrative curing agent comprising a blocked amine group and an alkoxy silane group is N-(1,3-dimethylbutylidene)aminopropyl-triethoxysilane, depicted as follows: Such curing agent is available from Gelest and from 3M as “3M™ Dynamer™ Rubber Curative RC5125”. Blocked amines are additional examples of electron donor precursors.

In some embodiments, the amine curing agent comprises an aziridine group and an alkoxy silane group. Such compounds are known for examples from US 3,243,429; incorporated herein by reference. Aziridine alkoxy silane compounds may have the general structure: wherein R” is hydrogen or a C ₁ -C ₄ alkyl (e.g. methyl);

X is a bond, a divalent atom, or a divalent linking group; n is 0, 1 or 2; m is 1, 2, or 3; and and the sum or n + m is 3.

One representative compound is 3-(2-methylaziridinyl) ethylcarboxylpropyltriethoxysilane.

Various other suitable aziridine crosslinkers are known, such as described in WO2014/075246; published May 22, 2014, incorporated herein by reference; and “NEW GENERATION OF MULTIFUNCTIONAL CROSSLINKERS,” (See https ://www.pstc .org/fdes/public/MilkerOO .pdf) .

The composition comprises a single (e.g. amine) electron donor compound or a combination of amine electron donor compounds may be present.

The amount of (e.g. amine) electron donor compound is typically at least 0.01 , 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, or 0.5% by weight solids (i.e. excluding the solvent of the coating composition), in some embodiments, the amount of (e.g. amine) electron donor compound is no greater than 5, 4.5, 4. 3.5, or 3% by weight solids.

In some embodiments, the fluoropolymer composition further comprises an alkoxy silane compound that lacks amine functionality. In some embodiments, such alkoxy silanes may be characterized as “non-functional” having the chemical formula:

R ² Si(OR ¹ ) _m wherein R ¹ is independently alkyl as previously described;

R ² is independently hydrogen, alkyl, aryl, alkaryl, or OR ¹ ; and m ranges from 1 to 3, and is typically 2 or 3 as previously described.

Suitable alkoxy silanes of the formula R ² Si(OR ¹ ) _m include, but are not limited to tetra-, tri-or dialkoxy silanes, and any combinations or mixtures thereof. Representative alkoxy silanes include propyltrimethoxysilane, propyltriethoxysilane, butyltrimethoxy silane, butyltriethoxysilane, pentyltrimethoxysilane, pentyltriethoxy silane, heptyltrimethoxy silane, heptyltriethoxy silane, octyltrimethoxysilane, octyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, hexadecyltrimethoxy silane, hexadecyltriethoxysilane, octadecyltrimethoxysilane, octadecyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxy silane dimethyldimethoxy silane and dimethyldiethoxy silane.

Preferably, the alkyl group(s) of the alkoxy silanes comprises from 1 to 6, more preferably 1 to 4 carbon atoms. Preferred alkoxysilanes for use herein are selected from the group consisting of tetra methoxysilane, tetra ethoxysilane, methyl triethoxysilane, dimethyldiethoxysilane, and any mixtures thereof. A preferred alkoxysilane for use herein comprises tetraethoxysilane (TEOS). The alkoxy silane lacking organofunctional groups utilized in the method of making the coating composition may be partially hydrolyzed, such as in the case of partially hydrolyzed tetramethoxysilane (TMOS) available from Mitsuibishi Chemical Company under the trade designation “MS-51”.

When present, the amount of alkoxy silane compound that lacks (amine/electron donor) functionality (e.g. TESO) is typically at least 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, or 0.5 % by weight solids (i.e. excluding the solvent of the coating composition). In some embodiments, the amount of alkoxy silane compound that lacks functionality is no greater than 5, 4.5, 4. 3.5, or 3 % by weight solids.

In typical embodiments, the composition described herein comprise a curing system comprising an ethylenically unsaturated compound in combination with an electron donor compound, such as an amine, in the absence of an organic peroxide. Organic peroxides are electron acceptors and thus would compete with the ionized halogen atom, thereby reducing crosslinking of the fluoropolymer. In some embodiments, the composition is also substantially free of other electron acceptors that would reduce crosslinking.

The fluoropolymer (coating solution) compositions comprises at least one solvent. The solvent is capable of dissolving the fluoropolymer. The solvent is typically present in an amount of at least 25% by weight based on the total weight of the coating solution composition. In some embodiments, the solvent is present in an amount of at least 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95% or greater based on the total weight of the coating solution composition.

The fluoropolymer (coating solution) composition typically comprises at least 0.01, 0.02, 0.03, 0.03, 0.04, 0.04, 0.05, 0.06, 0.7, 0.8. 0.9 or 1% by weight of fluoropolymer, based on the weight of the total coating solution composition. In some embodiments, the fluoropolymer coating solution composition comprises at least 2, 3, 4, or 5 % by weight of fluoropolymer. In some embodiments, the fluoropolymer coating solution composition comprises at least 6, 7, 8, 9 or 10 % by weight of fluoropolymer. The fluoropolymer coating solution composition typically comprises no greater than 50, 45, 40, 35, 30, 25, or 20% by weight of fluoropolymer, based on the weight of the total coating solution composition.

Optimum amounts of solvent and fluoropolymers may depend on the final application and may vary. For example, to provide thin coatings, very dilute solutions of fluoropolymer in the solvent may be desired, for example amounts of from 0.01 % by weight to 5 % by weight of fluoropolymer. Also for application by spray coating composition of low viscosity may be preferred over solutions with high viscosity. The concentration of fluoropolymer in the solution affects the viscosity and may be adjusted accordingly. An advantage of the present disclosure is that also solutions with high concentrations of fluoropolymer can be prepared that still provide clear liquid composition of low viscosity.

In some embodiments, the fluoropolymer coating solution compositions may be liquids. The liquids may have, for example, a viscosity of less than 2,000 mPas at room temperature (20 °C +/- 2 °C). In other embodiments, the fluoropolymer coating solution compositions are pastes. The pastes may have, for example, a viscosity of from 2,000 to 100.000 mPas at room temperature (20 °C +/- 2 °C).

The solvent is a liquid at ambient conditions and typically has a boiling point of greater than 50°C. Preferably, the solvent has a boiling point below 200°C so that it can be easily removed. In some embodiments, the solvent has a boiling point below 190, 180, 170, 160, 150, 140, 130, 120, 110, or 100°C.

The solvent is partially fluorinated or perfluorinated. Various partially fluorinated or perfluorinated solvents are known including perfluorocarbons (PFCs), hydrochlorofluorocarbons (HCFCs), perfluoropolyethers (PFPEs), and hydrofluorocarbons (HFCs), as well as fluorinated ketones and fluorinated alkyl amines.

In some embodiments, the solvent has a global warming potential (GWP, 100 year ITH) of less than 1000, 900, 800, 700, 600, 500, 400, 300, 200 or 100. The GWP is typically greater than 0 and may be at least 10, 20, 30, 40, 50, 60, 70, or 80. As used herein, GWP is a relative measure of the global warming potential of a compound based on the structure of the compound. The GWP of a compound, as defined by the Intergovernmental Panel on Climate Change (IPCC) in 1990 and updated in subsequent reports, is calculated as the warming due to the release of 1 kilogram of a compound relative to the warming due to the release of 1 kilogram of CO ₂ over a specified integration time horizon (ITH). where F is the radiative forcing per unit mass of a compound (the change in the flux of radiation through the atmosphere due to the IR absorbance of that compound), C _o is the atmospheric concentration of a compound at initial time, t is the atmospheric lifetime of a compound, t is time, and x is the compound of interest.

In some embodiments, the solvent comprises a partially fluorinated ether or a partially fluorinated polyether. The partially fluorinated ether or polyether may be linear, cyclic or branched. Preferably, it is branched. Preferably it comprises a non-fluorinated alkyl group and a perfluorinated alkyl group and more preferably, the perfluorinated alkyl group is branched.

In one embodiment, the partially fluorinated ether or polyether solvent corresponds to the formula:

Rf-O-R wherein Rf is a perfluorinated or partially fluorinated alkyl or (poly)ether group and R is a non- fluorinated or partially fluorinated alkyl group. Typically, Rf may have from 1 to 12 carbon atoms. Rf may be a primary, secondary or tertiary fluorinated or perfluorinated alkyl residue. This means, when Rf is a primary alkyl residue the carbon atom linked to the ether atoms contains two fluorine atoms and is bonded to another carbon atom of the fluorinated or perfluorinated alkyl chain. In such case Rf would correspond to R _f ¹ -CF ₂ - and the polyether can be described by the general formula: R _f ¹ -CF ₂ -O-R. When Rf is a secondary alkyl residue, the carbon atom linked to the ether atom is also linked to one fluorine atoms and to two carbon atoms of partially and/or perfluorinated alkyl chains and Rf corresponds to (R _f ² R _f ³ )CF-. The polyether would correspond to (R _f ² R _f ³ )CF-O-R.

When Rf is a tertiary alkyl residue the carbon atom linked to the ether atom is also linked to three carbon atoms of three partially and/or perfluorinated alkyl chains and Rf corresponds to (R _f ⁴ R _f ⁵ R _f ⁶ )-C-. The polyether then corresponds to (R _f ⁴ R _f ⁵ R _f ⁶ )-C-OR. R _f ¹ ; R _f ² ;

R _f ³ ; R _f ⁴ ; R _f ⁵ ; R _f ⁶ correspond to the definition of Rf and are a perfluorinated or partially fluorinated alkyl group that may be interrupted once or more than once by an ether oxygen. They may be linear or branched or cyclic. Also a combination of polyethers may be used and also a combination of primary, secondary and/or tertiary alkyl residues may be used.

An example of a solvent comprising a partially fluorinated alkyl group includes C ₃ F7OCHFCF ₃ (CAS No. 3330-15-2).

An example of a solvent wherein Rf comprises a perfluorinated (poly)ether is C3F ₇ OCF(CF ₃ )CF ₂ OCHFCF ₃ (CAS No. 3330-14-1).

In some embodiments, the partially fluorinated ether solvent corresponds to the formula:

CpF2p+1 -O-CqH2q+ 1 wherein q is an integer from 1 to and 5, for example 1, 2, 3, 4 or 5, and p is an integer from 5 to 11, for example 5, 6, 7, 8, 9, 10 or 11. Preferably, C _P F _2P+1 is branched. Preferably, C _P F _2p+1 is branched and q is 1, 2 or 3.

Representative solvents include for example 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy- 4-(trifluoromethyl)pentane and 3-ethoxy-1,1,1,2,3,4,4,5,5,6,6,6-dodecafluroro-2- (trifluoromethyl)hexane. Such solvents are commercially available, for example, under the trade designation NOVEC from 3M Company, St. Paul, MN.

The fluorinated (e.g. ethers and polyethers) solvents may be used alone or in combination with other solvents, which may be fluorochemical solvents or non-fluorochemical solvents. When a non-fluorochemical solvent is combined with a fluorinated solvent, the concentration non-fluorochemical solvent is typically less than 30, 25, 20, 15, 10 or 5 wt-% with respect to the total amount of solvent. Representative non-fluorochemical solvents include ketones such as acetone, MEK, methyl isobutyl ketone, methyl amyl ketone and NMP; ethers such as tetrahydrofuran, 2-methyl tetrahydrofuran and methyl tetrahydrofurfuryl ether; esters such as methyl acetate, ethyl acetate and butyl acetate; cyclic esters such as delta-valerolactone and gamma- valerolactone. In some embodiments, the composition further comprises crystalline fluoropolymer particles.

In one embodiment, such coating composition is prepared by blending a latex containing crystalline fluoropolymer particles with a latex containing amorphous fluoropolymer particles. The fluoropolymer particles typically have a small average particle diameter, for example less than 400 nm, but may be larger if especially when the applied coating will be rubbed after cure. For example, the fluoropolymer particle size range may be about 50 to about 1000 nm, or about 50 to about 400 nm, or about 50 to about 200 nm.

The latexes can be combined by any suitable manner such as by vortex mixing for 1-2 minutes. The method further comprises coagulating the mixture of latex particles. Coagulation may be carried out, for example, by chilling (e.g., freezing) the blended latexes or by adding a suitable salt (e.g., magnesium chloride). Chilling is especially desirable for coatings that will be used in semiconductor manufacturing and other applications where the introduction of salts may be undesirable. The method further comprising optionally washing the coagulated mixture of amorphous fluoropolymer particles and crystalline fluoropolymer particles. The washing step may substantially remove emulsifiers or other surfactants from the mixture and can assist in obtaining a well-mixed blend of substantially unagglomerated dry particles. In some embodiments, the surfactant level of the resulting dry particle mixture may, for example, be less than 0.1% by weight, less than 0.05 % by weight or less than 0.01 % by weight. The method further comprises drying the coagulated latex mixture. The coagulated latex mixture can be dried by any suitable means such as air drying or oven drying. In one embodiment, the coagulated latex mixture can be dried at 100°C for 1-2 hours.

The dried coagulated latex mixture can be dissolved in a solvent suitable for dissolving the amorphous fluoropolymer particles to form a stable coating composition containing a homogeneous dispersion of the crystalline fluoropolymer particles in a solution of the amorphous fluoropolymer.

The coating solution can be utilized to provide a coating on a substrate by applying a layer of the coating composition to a surface of a substrates and drying (i.e. removing the fluorinated solvent by evaporation) the coating composition.

In some embodiments, the method further comprises rubbing (e.g. buffing, polishing) the dried layer thereby forming an amorphous fluoropolymer binder layer containing crystalline submicron fluoropolymer particles.

The submicron crystalline fluoropolymer particles at the coating surface forms a thin, continuous or nearly continuous fluoropolymer surface layer disposed on the underlying coating comprised of the amorphous fluoropolymer. In preferred embodiments the thin crystalline fluoropolymer layer is relatively uniformly smeared over the underlying coating and appears to be thinner and more uniform than might be the case if the fluoropolymer particles had merely undergone fibrillation (e.g., due to orientation or other stretching).

Average roughness (Ra) of the surface is the arithmetic average of the absolute values of the surface height deviation measured from the mean planeln some embodiments, Ra is at least 40 or 50 nm, ranging up to 100 nm before rubbing. In some embodiments, the surface after rubbing is at least 10, 20, 30, 40, 50 or 60% smoother. In some embodiments, Ra is less than 35, 30, 25, or 20 nm after rubbing.

A variety of rubbing techniques can be employed at the time of coating formation or later when the coated article is used or about to be used. Simply wiping or buffing the coating a few times using a cheesecloth or other suitable woven, nonwoven or knit fabric will often suffice to form the desired thin layer. Those skilled in the art will appreciate that many other rubbing techniques may be employed. Rubbing can also reduce haze in the cured coating.

A variety of crystalline fluoropolymer particles may be employed including mixtures of different crystalline fluoropolymer particles. The crystalline fluoropolymer particles typically have high crystallinity and therefore a significant melting point (peak maximum) as determined by differential scanning calorimetry in accordance with DIN EN ISO 11357-3:2013-04 under nitrogen flow and a heating rate of 10°C/min.

For example, the crystalline fluoropolymer particles may include particles of fluoropolymers having a Tm of at least 100, 110, 120, or 130°C. In some embodiments, the crystalline fluoropolymer particles may include particles of fluoropolymers having a Tm no greater than 350, 340, 330, 320, 310 or 300°C.

The crystalline fluoropolymer particles typically have a fluorine content greater than about 50 weight percent. Also, the fluoropolymer particles may include particles of fluoropolymers having a fluorine content between about 50 and about 76 weight percent, between about 60 and about 76 weight percent, or between about 65 and about 76 weight percent.

Representative crystalline fluoropolymers include, for example, perfluorinated fluoropolymers such as 3M™ Dyneon™ PTFE Dispersions TF 5032Z, TF 5033Z, TF 5035Z, TF 5050Z, TF 5135GZ, and TF 5070GZ; and 3M™ Dyneon™ Fluorothermoplastic Dispersions PFA 6900GZ, PFA 6910GZ, FEP 6300GZ, and THV 340Z.

Other suitable fluoropolymer particles are available from suppliers such as Asahi Glass, Solvay Solexis, and Daikin Industries and will be familiar to those skilled in the art.

Commercial aqueous dispersion usually contain non-ionic and/or ionic surfactants at concentration up to 5 to 10 wt.%. These surfactants are substantially removed by washing the coagulated blends. A residual surfactant concentration of less than 1, 0.05, or 0.01 wt.% may be present. Quite often it is more convenient to use the “as polymerized” aqueous fluoropolymer-latexes as they do not contain such higher contents of non-ionic/ionic surfactants.

As previously described, the crystalline fluoropolymers have a melt point that can be determined by DSC. Crystallinity depends on the selection and concentration of polymerized monomers of the fluoropolymer. For example, PTFE homopolymers (containing 100 % TFE- units) have a melting point (Tm) above 340°C. The addition of comonomers, such as the unsaturated (per)fluorinated alkyl ethers, reduces the Tm. For example, when the fluoropolymer contains about 3-5 wt.% of polymerized units of such comonomer, the Tm is about 310 °C. As yet another example, when the fluoropolymer contains about 15-20 wt.% of polymerized units of HFP, the Tm is about 260-270°C. As yet another example, when the fluoropolymer contains 30 wt.% of polymerized units of (per)fluorinated alkyl ethers (e.g. PMVE) or other comonomer(s) that reduce the crystallinity the fluoropolymer no longer has a detectable melting point via DSC, and thus is characterized as being amorphous.

In some embodiments, the crystalline fluoropolymer particles contain at least 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or about 100 wt.% of polymerized units of TFE. Further, the crystalline fluoropolymer particles typically comprise a lower concentration of unsaturated (per)fluorinated alkyl ethers (e.g. PMVE) than the amorphous flurorpolymer. In typical embodiments, the crystalline fluoropolymer particles contain less than 30, 25, 20, 15, 10, or 5 wt.% of polymerized units of (per)fluorinated alkyl ethers (e.g. PMVE).

In some embodiments, the crystalline fluororpolymers are copolymers formed from the constituent monomers known as tetrafluoroethylene (“TFE”), hexafluoropropylene (“HFP”), and vinylidene fluoride (“VDF,” “VF2,”). The monomer structures for these constituents are shown below:

TFE: CF ₂ =CF ₂ (1)

VDF: CH ₂ =CF ₂ (2)

HFP: CF ₂ =CF-CF ₃ (3)

In some embodiments, the crystalline fluoropolymer consists of at least two of the constituent monomers (HFP and VDF), and in some embodiments all three of the constituents monomers in varying amounts. The Tm depends on the amounts of TFE, HFP, and VDF. For example, a fluoropolymer comprising about 45 wt.% of polymerized units of TFE, about 18 wt.% of polymerized units of HFP, and about 37 wt.% of polymerized units of VDF has a Tm of about 120°C. As yet another example, a fluoropolymer comprising about 76 wt.% of polymerized units of TFE, about 11 wt.% of polymerized units of HFP, and about 13 wt.% of polymerized units of VDF has a Tm of about 240°C. By Increasing the polymerized units of HFP/VDF, while reducing the polymerized units of TFE, the fluoropolymer becomes amorphous. An overview of crystalline and amorphous Fluoropolymers is given in: Ullmann’s Encyclopedia of Industrial Chemistry (7 ^th Edition, 2013 Wiley-VCH Verlag. 10. 1002/14356007.al 1 393 pub 2) Chapter: Fluoropolymers, Organic.

The crystalline fluoropolymer particles and amorphous fluoropolymer particles may be combined in a variety of ratios. For example, the coating composition contains about 5 to about 95 weight percent crystalline fluoropolymer particles and about 95 to about 5 weight percent amorphous fluoropolymer, based on the total weight percent of solids (i.e. excluding the solvent). In some embodiments, the coating composition contains about 10 to about 75 weight percent crystalline fluoropolymer particles and about 90 to about 25 weight amorphous fluoropolymer.

In some embodiments, the coating composition contains about 10 to about 50 weight percent crystalline fluoropolymer particles and about 90 to about 50 weight percent amorphous fluoropolymer. In some embodiments, the coating composition contains about 10 to about 30 weight percent crystalline fluoropolymer particles and about 90 to about 70 weight percent amorphous fluoropolymer.

Compositions containing curable fluoroelastomers may further contain additives as known in the art. Examples include acid acceptors. Such acid acceptors can be inorganic or blends of inorganic and organic acid acceptors. Examples of inorganic acceptors include magnesium oxide, lead oxide, calcium oxide, calcium hydroxide, dibasic lead phosphate, zinc oxide, barium carbonate, strontium hydroxide, calcium carbonate, hydrotalcite, etc. Organic acceptors include epoxies, sodium stearate, and magnesium oxalate. Particularly suitable acid acceptors include magnesium oxide and zinc oxide. Blends of acid acceptors may be used as well. The amount of acid acceptor will generally depend on the nature of the acid acceptor used. Typically, the amount of acid acceptor used is between 0.5 and 5 parts per 100 parts of fluorinated polymer.

The fluoropolymer composition may contain further additives, such as stabilizers, surfactants, ultraviolet (“UV”) absorbers, antioxidants, plasticizers, lubricants, fdlers, and processing aids typically utilized in fluoropolymer processing or compounding, provided they have adequate stability for the intended service conditions. A particular example of additives includes carbon particles, like carbon black, graphite, soot. Further additives include but are not limited to pigments, for example iron oxides, titanium dioxides. Other additives include but are not limited to clay, silicon dioxide, barium sulphate, silica, glass fibers, or other additives known and used in the art.

The fluoropolymer compositions may be prepared by mixing the polymer, the curing agent(s) including at least one ethylenically unsaturated curing agent, at least one compound with an electron donor group, optional additives and the fluorinated solvent. In some embodiments, the fluoropolymer is first dissolved in the fluorinated solvent and the other additives, including the curing agent(s) and electron donor compound are added thereafter.

The coating composition described herein including fluorinated solvent is “stable, meaning that the coating composition remains homogeneous when stored for at least 24 hours at room temperature in a sealed container. In some embodiments, the coating composition is stable for one week or more. “Homogeneous” refers to a coating composition that does not exhibit a visibly separate precipitate or visibly separate layer when freshly shaken, placed in a 100 ml glass container and allowed to stand at room temperature for at least 4 hours.

In some embodiments, the fluoropolymer is first combined with other solid ingredients and in particular with the electron donor (e.g. amine) compounds and ethylenically unsaturated curing agent described herein. The fluoropolymer and amine compounds can be combined in conventional rubber processing equipment to provide a solid mixture, i.e. a solid polymer containing the additional ingredients, also referred to in the art as a "compound". Typical equipment includes rubber mills, internal mixers, such as Banbury mixers, and mixing extruders. During mixing the components and additives are distributed uniformly throughout the resulting fluorinated polymer "compound" or polymer sheets. The compound is then preferably comminuted, for example by cutting it into smaller pieces and is then dissolved in the solvent.

The fluoropolymer coating solution compositions provided herein are suitable for coating substrates. The fluoropolymer coating solution compositions may be formulated to have different viscosities depending on solvent and fluoropolymer content and the presence or absence of optional additives. The fluoropolymer coating solution compositions typically contain or are solutions of fluoropolymers and may be in the form of liquids or pastes. Nevertheless, the compositions may contain dispersed or suspended materials but these materials preferably are additives and not fluoropolymers of the type as described herein. Preferably, the compositions are liquids and more preferably they are solutions containing one or more fluoropolymer as described herein dissolved in a solvent as described herein. The fluoropolymer compositions provided herein are suitable for coating substrates and may be adjusted (by the solvent content) to a viscosity to allow application by different coating methods, including, but not limited to spray coating or printing (for example but not limited to ink-printing, 3D-printing, screen printing), painting, impregnating, roller coating, bar coating, dip coating and solvent casting.

Coated substrates and articles may be prepared by applying the fluoropolymer compositions to a substrate and removing the solvent. The curing may occur to, during, or after removing the solvent. The solvent may be reduced or completely removed, for example for evaporation, drying or by boiling it off. After removal of the solvent the composition may be characterized as “dried”.

Methods of making a crosslinked fluoropolymer described herein comprise curing the fluoropolymer with (e.g. UV or e-beam) actinic irradiation. The fluoropolymer composition, substrate, or both are transmissive to the curing radiation. In some embodiments, a combination of UV curing and thermal (e.g. post) curing is utilized. The curing is carried out at an effective temperature and effective time to create a cured fluoroelastomer. Optimum conditions can be tested by examining the fluoroelastomer for its mechanical and physical properties. Curing may be carried out under pressure or without pressure in an oven. A post curing cycle at increased temperatures and or pressure may be applied to ensure the curing process is fully completed. The curing conditions depend on the curing system used.

In some embodiments, the composition is cured by UV-curing. The fluoropolymers of the compositions described here comprise little or no polymerized units of vinylidene fluoride (VDF) (i.e. CH ₂ =CF ₂ ) or VDF coupled to hexafluoropropylene (HFP). Polymerized units of VDF can undergo dehydrofluorination (i.e. an HF elimination reaction) as described in US2006/0147723. The reaction is limited by the number of polymerized VDF groups coupled to an HFP group contained in the fluoropolymer. The double bonds created as a result of dehydrofluorination can then react (via Michael addition) with an amino alkoxy silane thereby grafting fluorinated pendent alkoxy silane groups onto the fluoropolymer backbone. When irradiated with UV light, such pendent groups can free-radically copolymerize with multifunctional (meth)acrylate compounds.

However, since the fluoropolymers of the compositions described here comprise little or no polymerized units of VDF (i.e. CH ₂ =CF ₂ ) coupled to an HFP group, the fluoropolymers are not susceptible to the reaction schemes just described. As evident by the forthcoming examples, the amine compound alone can initiate UV-curing in the absence of free-radical photoinitiators. The inclusion of free-radical photoinitiator typically does not increase the crosslinking of the fluoropolymer. This result suggests that the fluoropolymer is not crosslinked via a free-radical mechanism.

Although, conventional free-radical initiators are not required, the composition can optionally further comprise a photoinitiator. In other embodiments, the composition is substantially free of free -radical initiators including such free -radical photoinitiators.

In some embodiments, the UV radiation may have sufficient intensity at a wavelength of at least 190 nm, 200 nm, 210 nm, 220 nm, 230 nm or 240 nm. In some embodiments, the UV radiation may have sufficient intensity at a wavelength no greater than 350 nm, 340 nm,

330 nm, 320 nm, 310 nm, or 290 nm. In some embodiments, the (e.g. UV) actinic radiation has sufficient intensity at a wavelength ranging from 270-290 nm such that in the presence of an (e.g. amine) electron donor a wavelength-induced single electron transfer reaction may occur between C-I bonds. In some embodiments, the UV radiation may have sufficient intensity at a wavelength ranging below 240 nm (e.g. 150-200 nm) such that in the presence of an (e.g. amine) electron donor a wavelength-induced single electron transfer reaction may occur between C-Cl or C-Br bonds.

UV light sources can be of various types. Uow light intensity sources, such as blacklights, generally provide intensities ranging from 0.1 or 0.5 mW/cm ² (millwatts per square centimeter) to 10 mW/cm ² (as measured in accordance with procedures approved by the United States National Institute of Standards and Technology as, for example, with a UVIMAP UM 365 U-S radiometer manufactured by Electronic Instrumentation & Technology, Inc., in Sterling, VA). High light intensity sources generally provide intensities greater than 10, 15, or 20 mW/cm ² ranging up to 450 mW/cm ² or greater. In some embodiments, high intensity light sources provide intensities up to 500, 600, 700, 800, 900 or 1000 mW/cm ² . UV light to polymerize the ethylenically unsaturated monomer(s) can be provided by various light sources such as light emitting diodes (UEDs), fluorescent blacklights, arc-lamps such as xenon-acre lamps and medium and low pressure mercury lamps (including germicidal lamps), microwave- driven lamps, lasers etc. or a combination thereof. The composition can also be polymerized with higher intensity light sources as available from Fusion UV Systems Inc. Lamps that emit ultraviolet or blue light are typically preferred. The UV exposure time for polymerization and curing can vary depending on the intensity of the light source(s) used. For example, complete curing with a low intensity light course can be accomplished with an exposure time ranging from about 30 to 300 seconds; whereas complete curing with a high intensity light source can be accomplished with shorter exposure time ranging from about 5 to 20 seconds. Partial curing with a high intensity light source can typically be accomplished with exposure times ranging from about 2 seconds to about 5 or 10 seconds. In some embodiments, post curing may be carried out at a temperature between 170°C and 250°C for a period of 0.1 to 24 hours.

In some embodiments, post curing of the fluoropolymer may optionally be carried out at lower temperatures. Post curing at lower temperatures is amenable for coating heat sensitive substrates. In some embodiments, the post curing occurs at a temperature ranging from 100,

110, 120, 130, 135 or 140°C up to 170°C for a period of 5-10 minutes to 24 hours. In some embodiments, the temperature is no greaterthan 169, 168, 167, 166, 165, 164, 163, 162, 161, or 160°C. In some embodiments, the temperature is no greaterthan 135, 130, 125, or 120°C. In favored embodiments, after curing the fluoropolymer is sufficiently crosslinked such that at least 80, 85, 90, 95 or 100 wt.% or greater cannot be dissolved (within 12 hours at 25°C) in fluorinated solvent (e.g. 3-ethoxy perfluorinated 2-methyl hexane) at a weight ratio of 5 grams of fluoropolymer in 95% by weight of fluorinated solvent.

The compositions may be used for impregnating substrates, printing on substrates (for example screen printing), or coating substrates, for example but not limited to spray coating, painting dip coating, roller coating, bar coating, solvent casting, paste coating. The substrate may be organic, inorganic, or a combination thereof. Suitable substrates may include any solid surface and may include substrate selected from glass, plastics (e.g. polycarbonate), composites, metals (stainless steel, aluminum, carbon steel), metal alloys, wood, paper among others. The coating may be coloured in case the compositions contains pigments, for example titanium dioxides or black fillers like graphite or soot, or it may be colorless in case pigments or black fillers are absent.

Bonding agents and primers may be used to pretreat the surface of the substrate before coating. For example, bonding of the coating to metal surfaces may be improved by applying a bonding agent or primer. Examples include commercial primers or bonding agents, for example those commercially available under the trade designation CHEMLOK. Articles containing a coating from the compositions provided herein include but are not limited to impregnated textiles, for example protective clothing. Textiles may include woven or non-woven fabrics. Other articles include articles exposed to corrosive environments, for example seals and components of seals and valves used in chemical processing, for example but not limited to components or linings of chemical reactors, molds, chemical processing equipment for example for etching, or valves, pumps and tubings, in particular for corrosive substances or hydrocarbon fuels or solvents; combustion engines, electrodes, fuel transportation, containers for acids and bases and transportation systems for acids and bases, electrical cells, fuel cells, electrolysis cells and articles used in or for etching. An advantage of the coating compositions described herein is that the coating compositions can be used to prepare coatings or fluuoroplymer sheets of high or low thickness. In some embodiments, the dried and cured fluoropolymer has a thickness of 0.1 microns to 1 or 2 mils. In some embodiments, the dried and cured fluoropolymer thickness is at least 0.2, 0.3, 0.4, 0.5, or 0.6 microns. In some embodiments, the dried and cured fluoropolymer thickness is at least 1, 2, 3, 4, 5, or 6 microns.

In typical embodiments, the dried and cured (i.e. crosslinked) composition has a low dielectric constant (Dk), typically less than 2.75, 2.70, 2.65, 2.60, 2.55, 2.50, 2.45, 2.40, 2.35, 2.30, 2.25, 2.20, 2.15, 2.20, 2.15. In some embodiments, the dielectric constant is at least 2.02, 2.03, 2.04, 2.05. The dried and cured (i.e. crosslinked) composition has a low dielectric loss, typically less than 0.01, 0.009, 0.008, 0.007, 0.006, 0.005, 0.004, 0.003, 0.002, 0.001, 0.0009, 0.0008, 0.0007, 0.0006, 0.0005, 0.0004, 0.0003. In some embodiments, the dielectric loss is at least 0.00022, 0.00023, 0.00024, 0.00025.

The dried and cured coating can exhibit good adhesion to various substrates (e.g. glass, polycarbonate,), as evidence by the coating exhibiting a 2, and preferably a 3 or 4 according to the Boiling Water Test described in the examples. In favored embodiments, the dried and cured coating is durable as evidence by the coating exhibiting a 2, and preferably a 3 or 4 according to the Abrasion Test described in PCT/US2019/036460; incorporated herein by reference. In some embodiments, the coating is durable, according to the Abrasion Test after being subjected to the Boiling Water Test.

In some emboidments, the dried and cured coating has good hydrophobic and oleiphobic properties according to the Black Permanent Marker Resistance Test described in previousyl cited PCT/US2019/036460, i.e. the marker fluid beads and is easy to remove with a paper towel or cloth.

In some embodiments, the dried and cured coating has good hydrophobic and oleiphobic properties, as determined by Contact Angle Measurements (as determined according to the test method described in the examples). In some embodiments, the advancing and/or receding contact angle with water can be at least 100, 105, 110, 115, 120, 125 or 130 degrees.

In some embodiments, the advancing and/or receding contact angle with hexadecane can be at least 60, 65, 70, or 75 degrees. In some embodiments, the coating exhibits such contact angles, after being subjected to the Boiling Water Test or after being subject the Boiling Water Test and the Abrasion Test (as determined according to the test method described in previously cited PCT/US2019/036460). In some embodiments, the dried and cured coating exhibits good corrision resistance (i.e. not corroded) according to the Acid/Base Corrison Test described in previousyl cited PCT/US2019/036460.

As used herein the term “partially fluorinated alkyl” means an alkyl group of which some but not all hydrogens bonded to the carbon chain have been replaced by fluorine. For example, an F ₂ HC-, or an FH ₂ C- group is a partially fluorinated methyl group. Alkyl groups where the remaining hydrogen atoms have been partially or completely replaced by other atoms, for example other halogen atoms like chlorine, iodine and/or bromine are also encompassed by the term “partially fluorinated alkyl” as long as at least one hydrogen has been replaced by a fluorine. For example, residues of the formula F ₂ CIC- or FHCIC- are also partially fluorinated alkyl residues.

A “partially fluorinated ether” is an ether containing at least one partially fluorinated group, or an ether that contains one or more perfluorinated groups and at least one non- fluorinated or at least one partially fluorinated group. For example, F ₂ HC-O-CH ₃ , F ₃ C-O-CH ₃ , F ₂ HC-O-CFH ₂ , and F ₂ HC-O-CF ₃ are examples of partially fluorinated ethers. Ethers groups where the remaining hydrogen atoms have been partially or completely replaced by other atoms, for example other halogen atoms like chlorine, iodine and/or bromine are also encompassed by the term “partially fluorinated alkyl” as long as at least one hydrogen has been replaced by a fluorine. For example, ethers of the formula F ₂ CIC-O-CF ₃ or FHCIC-O-CF ₃ are also partially fluorinated ethers.

The term “perfluorinated alkyl” or “perfluoro alkyl” is used herein to describe an alkyl group where all hydrogen atoms bonded to the alkyl chain have been replaced by fluorine atoms. For example, F ₃ C- represents a perfluoromethyl group.

A “perfluorinated ether” is an ether of which all hydrogen atoms have been replaced by fluorine atoms. An example of a perfluorinated ether is F ₃ C-O-CF ₃ .

The following examples are provided to further illustrate the present disclosure without any intention to limit the disclosure to the specific examples and embodiments provided.

EXAMPLES

Unless otherwise noted or readily apparent from the context, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight. Table 1. Materials:

Preparation of Fluorinated Ether Diene

A fluorinated ether diol, HO-CH ₂ -CF ₂ -O-(CF ₂ CF ₂ )CF ₂ -CH ₂ -OH (0.16 mol), having an average molecular weight of 1500, and an average hydroxyl functionality of 1.8 as described in US5384374 was allowed to react with sodium methoxide (0.34 mol) and subsequently to react with allyl bromide (40g, 0.36 mol) in a 250 mL 3-necked flask with a condenser at 60°C overnight. After reaction, the reaction mixture was washed with water and a pale-yellow liquid was dried over CaCI ₂ before rotavapor to remove any residue of ally bromide.

General procedure - Perfluoroelastomer PFE coating solution preparation with multifunctional alkene/aminosilane ester photocrosslinkers:

Perfluoroelastomer PFE 40, 60 or 90 solutions were prepared by cutting PFE 40, 60, 90 gums separately into small pieces and adding them into HFE solvent (FIFE-7300 or FIFE-7500) to make a 10 wt.% PFE in HFE solution (10 g PFE and 90 g HFE). The containers were sealed with PTFE tape and paraffin film. The solution was subject to vigorous shaking overnight (~ 12 hours) to become completely homogenous.

All the aminosilanes, initiators were dissolved or dispersed in HFE to form 1 wt.% or 5 wt.% solutions or suspensions (e.g. 0.5 g TAIC was added to 9.5 g HFE to form a 5 wt.% suspension in a vial). To the PFE solution was added an amine (e.g. aminosilane), an alkene and, optionally, a photo-initiator. For example, sample (5% TAIC, 1% APES, 2% TMOS) was prepared by adding 0.3157 g TAIC suspension (5 wt.% in HFE), 0.0606 g APES suspension (5 wt.% in HFE), and 0.1224 g TMOS solution (5 wt.% in 7500) to 3 g PFE 40 solution (10 wt.% in PFE 40). Many silanes form suspensions, rather than solutions in HFE. Such suspensions were homogenized using a vortex shaker at 1000 rpm for 10 seconds to form well dispersed slurry before being added to the PFE-HFE solution. Also, the percentage in the formula (e.g., 5%, 3%, 1%) was the mass fraction based on the solid content of PFE (e.g. PFE 40 + 5% APES + 2% 1173 means: the solid content of PFE40 /APES = 95: 5 and the solid content of PFE40 /1173 = 98: 2) General procedure - Perfluoroelastomer PFE coating solution preparation with fluorinated alkene/aminosilane ester photo-crosslinkers:

In a similar fashion as described above, perfluoroelastomer PFE 40, 60 or 90 solutions were prepared by cutting PFE 40, 60, 90 gums separately into small pieces and placing them into HFE solvent to obtain 10 wt.% solutions of PFE in HFE in a glass jar. The glass jar was sealed with Teflon tape and paraffin film. The solution was subjected to vigorous shaking overnight (~ 12 hours) until completely homogenous. Most alkenes were dissolved or dispersed in HFE to form 1 wt.% or 5 wt.% solution or suspension. Alkenes were dissolved in methanol or methoxy propanol instead when there was rapid phase separations between the alkenes and HFE solution and when the alkene sample was solid at room temperature and could not be completely dispersed in HFE7500. These alkenes include 4,4'-bis((1,2,2- trifluorovinyl)oxy)-1,1'-biphenyl (dissolved in methanol), Chloro-1,2-phenylene diacrylate (dissolved in methanol), Perchloro-1,2-phenylene diacrylate (dissolved in methoxy propanol), 2,4,6-tribromobenzene-1,3,5-triyl triacrylate (dissolved in methoxy propanol)). In addition to alkenes, all the silanes and photoinitiators were dissolved or dispersed in HFE to form lwt.% or 5 wt.% solutions or suspensions. To PFE was added an alkene or a multifunctional alkene and other chemicals including silanes and initiators as indicated in Tables.

Table 2. Crosslinking Yield of Cured Fluoropolymers

For the crosslinking yield studies, samples were prepared by depositing a 3g solution onto PET film. The coated film was dried at ambient temperature for 2 hours and at 50°C for 20 min. After the samples were completely dried, the PET film samples were placed on a wooden or a stainless steel board and cured under a single 500 watt H-bulb or 500 watt D-bulb UV lamp for 5-10 runs with a speed of 30 ft per minute (as indicated in the tables). After UV curing, many samples were also thermally cured at 120°C for 5 min in an oven (as indicated in tables). Some of the same samples were also subjected to thermal curing conditions without UV curing.

The UV cured samples (1-2 mils in thickness) were peeled off from the PET film, weighed, and then dissolved with HFE in a vial. The mass ratio of cured PFE sample/HFE solvent was 5/95. The vial was subjected to vigorous shaking overnight (~ 12 hours) before any observation was recorded as described in the following table. The precipitated samples (i.e. crosslinked PFE) in the HFE solutions were collected, dried and weighed. In some instances, the gel (i.e. less crosslinked PFE) was collected, dried, and weighed.

Table 3. Effect of an aminosilane ester on photochemically crosslinking PFE-1 with TAIC

Table 4. Effect of an organic amine on photochemically crosslinking PFE-1 with TAIC Table 5. Effect of alkenes on photochemically crosslinking PFE-1 with TAIC Table 6. Influence of wavelength (H-Bulb and D-Bulb) and the number of UV cure runs on UV crosslinking of PFE-1 + TAIC + APES Table 7. Influence of wavelength (H-Bulb and D-Bulb) on UV crosslinking of PFE-1 + Alkene + Amine

Table 8. Effect of an aminosilane ester on photochemically crosslinking PFE-2 with alkenes Table 9. Influence of wavelength (H-Bulb and D-Bulb) on UV crosslinking of PFE-2 + TAIC

Table 10. Photochemically crosslinked PFE-1 (UV cure only or UV + thermal cure) at 120 °C for 5 minutes

Preparation of PFE 40 Coated Dispersed Crystalline Fluoropolymer Particles:

Perfluoroelastomer latex PFE-1 was mixed with crystalline fluoropolymer latexes PFA, PTFE, or with THV respectively at the weight ratios described in the Table 11. The solutions were vortex mixing for 1-2 minutes. Subsequently, the well-mixed solutions were froze at -20 °C temperature for 4 hours, and then taken out and thawed in warm water. After thawing, the precipitates were filtered and washed with deionized (DI) water. The obtained solids were dried in an oven at 100 °C for 1-2 hours. The dried coagulated solids were mixed with HFE to form a 10 wt.% solution in HFE. TAIC and APS was also added to the HFE composition as indicated in Table 11. Each composition was placed in a shaker for 3-4 hours obtaining a stable and well-dispersed homogeneous composition.

Samples were prepared by depositing a 3g solution onto PET film. The coated film was dried at ambient temperature for 2 hours and at 50 °C for 20 min. After the samples were completely dried, the PET film samples were placed on a wooden or a stainless steel board and cured under a single 500 watt H-bulb for 5-10 runs with a speed of 30 ft per minute (as indicated in the tables). After UV curing, some samples were also thermally cured at 120 °C for 5 min in an oven (as indicated in Table 11).

The UV cured samples (1-2 mils in thickness) were peeled off from the PET film, weighed, and then dissolved with HFE in a vial. The mass ratio of cured PFE sample/HFE solvent was 5/95. The vial was subjected to vigorous shaking overnight (~ 12 hours) before any observation was recorded as described in the following table. The precipitated samples (i.e. crosslinked PFE) in the HFE solutions were collected, dried and weighed.

Table 11. Crystalline Fluoropolymer Particles Coated with Photochemically Crosslinked PFE-1