SEM1-FLUORINATED THERMOPLASTIC RESINS WITH LOW GEL CONTENT

Technical mM

The present description reiates to tetrafluoroethene-based polymers with low ge! content. The polymers are suitable for making extrusion products. The description also relates to extrusion products containing the tetrafiuoroeihene-based polymers and to methods for making and extruding the ieirafluoroethene-based polymers. Background

Fluoropo!ymers have been used in a variety of applications because of several desirable properties such as heat resistance, chemical resistance, weatherability, and UV~ stability.

Fluoropoiymers include, for example, homo and co-polymers of a gaseous fluorinated olefin such as tetrafluoroethene (TFE), chiorotrifiuoroethene (CTFE) and/or vinylidene fluoride (VDF) with one or more gaseous or liquid co nonomers such as he afiuoropropene (HFP) or

perfiuorovinyi ethers (PVE) or pefluoroallyl ethers (PAVE) or non- fiuorinated olefins such as ethene (E) and propane (P).

Homopo!ymers of tetraffu roethene (PTFE) are highly resistant materials with a very high servic temperature. However, PTFE is not melt processable by standard melt extrusion equipment because of its extremely high melt viscosity. Therefore, various TFE copolymers have been developed that are thermoplastic and have a reduced melt viscosity making them meSt-processab!e by ordinary melt-processing equipment. Examples of such fluoropoiymers include the fluoropoiymer classes PFA (copolymers comprising TFE and perfiuorinated vinyl ethers), FEP (copolymers comprising TFE and HFP), THV (copolymers comprising TFE, HFP and VDF), HTE (copolymers comprising TFE, HFP and E), TFE-E (copolymers of TFE and E), TFE-P (copolymers of TFE and P), PVDF (homopoiymers of VDF).

elt-processab!e thermoplastic fluoropoiymers have been used in the preparation of extruded articles like sheets, layers, tubes etc. or in extrusion coatings like for example in the cable and wire industry. Thermoplastic fluoropoiymers typically are meit-extrudab!e. Melt- extrudab!e polymers have a melting point, which means they are substantially crystalline materials. During melt-processing of thermoplastic fluoropoiymers various melt defects can occur. For example, in extrusion processes the rate of extrusion of a fluorothermoplasi is limited to the speed (known as critical shear rate) at which the polymer melt undergoes melt fracture. Melt fracture leads to an undesired rough surface of the extruded article (also referred to in the art as "shark skin"). Therefore, the critical shear rate of thermoplasts is typically determined and indicated in the supplier's data sheets. These defects typically occur only on the surface of the polymer and may be predominantly or exclusively caused by the melt-processing equipment or the condition at which the melt-processing is carried out. Various means are available to increase the critical shear rate of a thermopiast to a! low for faster meii -processing rates, which is economically advantageous. One exampie is the use of additives {processing aids), Other attempts have relied on broadening the molecular weight distribution of the polymers or on using bimoda! or multimodal polymer compositions, i.e. polymer compositions with distinct populations of po!ymers having distinctively different molecular weights. Alternatively, modifying the polymer architecture may also improve the melt-processing of the respective

fiuorothermoplast. For example, in WO2009/009361 , the introduction of iong chain branches to substantially linear polymers has been described to lead to improved melt processing and meit processed products, for example films and tubes having more homogeneous surfaces,

Other defects may be present in extruded products that are not (oniy) surface defects.

Such Internal" defects may be caused by polymer fractions within the poiymer composition that are believed to form geis during melt processing rather than melt. Such fractions are believed to be polymer coagulates created during the polymerization reaction. Typically these defects appear as substantially spherical, circular or oval inhomogeneities in the extruded product and are referred to in the art as "bubbles" or "fish eyes" or simply as "gel content". Polymers with high get content will lead to extrusion products of poor visual appearance, either caused by defects in the extruded poiymer or by leading to inhomogeneous distribution of adjuvants likes pigments or filters in the extrusion product.

Thermoplastic TFE -based fluoropo!ymers are believed to be prone to have an increased "gel content" with increasing melting points. However, higher melting fluoropoplymers are desired in many applications as they allow for higher service temperatures and greater processing windows. For exampie. high processing temperatures may be required in lamination processes of fiuoropolymer sheets to form multi-layer articles or during encapsulation processes using high melting encapsulants to form sealed fiuoropolymer products as are often required, fo example, in the manufacture of so!ar modules.

Therefore, there is a need for thermoplastic fluaropoiymers, and in particular melt- processed fluoropolymers, having high melting points, for example melting points of at least 170°C that can be conveniently melt-processed, e.g. melt-extruded, and that can be extruded into films having an increased visual appearance, for example by having a reduced gel content,

Summary

In one aspect of the present disclosure ther is provided a tetrafluoroethene-hased fiuoropolymer, having an MFI {265/5} of from about 13 to about 30 g/10 min, a melting point of from about 170°C to about 230 ^a C, wherein the tetrafluoroethene- ased fiuoropolymer is a copolymer comprising more than 52 % by weight based on the weight of the polymer of units derived from tetrafluoroethene and is selected from copolymers comprising interpolymerized units of tetrafluoroethene and ethene or interpolymerized units of tetrafluoroethene and hexafluoropropene, wherein the tetrafluoroethene-based fiuoropolymer is obtainable by a radical aqueous emulsion polymerization in the presence of one or more fiuorinated emulsifiers of the general formula

R _f O-L-CCV X ^* (!) wherein Rf is selected from a partially or fully fiuorinated aikyi group that may optionally be interrupted with one or more oxygen atoms; L is selected from a partially or fully fiuorinated linear or branched alkylene group thai is optionally interrupted with one or more oxygen atoms, and X ^* represents a cation or H ⁺ ,

and one or more fiuorinated liquids selected from saturated partially or perfluorinated hydrocarbons which may contain one or more catenary heteroatoms selected from oxygen and/or nitrogen and have a boiling point of greater than 50°C,

In another aspect there is provided a tetrafluoroethene-based f!uoropo!ymer, having an !vlFI (265/5) of from about 13 g/10 min to about 30 g/10 min and a melting point beiween 17Q°C an 230 ^C C, wherein the tetrafluoroethene-based polymer is a copolymer selected from copolymers comprising interpolymerized units of tetrafiuoroethene and ethene or

interpolymerized units of tetrafiuoroethene and hexafluoropropene, wherein the copolymer comprises more than 52 % by weight based on the weight of the copolymer of units derived from tetrafiuoroethene and wherein the fluoropoiymer has a gel content of less than 3,000 / m ² . in yet another aspect there is provided an extrusion product comprising a

tetrafluoroethene-based fluoropoiymer, having an FI (285/5) of from about 13 g/ 0 min to about 30 g/10 min and a melting point between 170 ^* 0 an 230°C, wherein the tetrafiuoroethene- based polymer is a copolymer selected from copolymers comprising interpolymerized units of tetrafiuoroethene and ethene or interpolymerized units of tetrafiuoroethene and

hexafluoropropene, wherein the fluoropoiymer comprises more than 52 % by weight based on the weight of the polymer of units derived from tetrafiuoroethene and has a gel content of less than 3,000 / m*.

In a further aspect there is provided a multi-layer article comprising an extruded sheet comprising a tetrafluoroethene-based fluoropoiymer, having an MFS (265/5) of from about 13 g/10 min to about 30 g/10 min and a melting point between 170 ^C C an 23Q ^<: C, wherein the tetrafluoroethene-based fluoropoiymer is a copolymer comprising more than 52 % by weight based on the weight of the polymer of units derived from tetrafiuoroethene and is selected from copolymers comprising interpolymerized units of tetrafiuoroethene and ethene or

interpolymerized units of tetrafiuoroethene, and hexafluoropropene and wherein the

fluoropoiymer has a gel content of less than 3,000 m ^¾ .

In yet another aspect there is provided a process of making an extruded article comprising providing

(i) a composition comprising a tetrafluoroethene-based fluoropoiymer, having an IVSFI (265/5) of from about 13 to about 30 g/10 min, a melting point of from about 170°C to about 230 ^: C, wherein the tetraf!uoroethene-based fiuoropolymer is a copo!ymer comprising more than 52 % by weight based on the weight of the polymer of units derived from tetrafluoroethene ands selected from copolymers comprising interpoiymerized units of tetrafluoroethene and ethene or interpoiymerized units of tetrafluoroethene and hexafiuoropropene. wherein the

ietrafluoroethene-based fiuoropolymer is obtainabie by a radical aqueous emulsion

polymerization in the presence of one or more fluorinaied emu!sifiers of the general formula wherein Rf is selected from a partially or fully fluorinated aikyi group that may optionally be interrupted with one or more oxygen atoms; L is selected from a partially or fully fluorinated linear or branched alkylene group thai is optionaiiy interrupted with one or more oxygen atoms, and X ^* represents a cation or H ⁺ ,

and one or more fluorinated liquids selected from saturated partially or perf!uorinated hydrocarbons which may contain one or more catenary heteroatoms selected from oxygen and/or nitrogen and having a boiling point of greater than 50 ^* 0, and

(si) subjecting the composition to meit-extrusion to obtain an extruded article.

In a further aspect there is provided a process of making an extruded article comprising providing

(i) a composition comprising a tetraf!uoroethene-based fiuoropolymer having an Fi (265/5) of from about 13 g/10 in to about 30 g/10 win and a melting point between T7Q°C an 230°C. wherein the tetrafSuoroethene-based fiuoropolymer comprises interpoiymerized units of tetrafluoroethene and ethene or interpoiymerized units of tetrafluoroethene and

hexafiuoropropene, and comprises more than 52 % by weight, based on the weight of the fiuoropolymer, of units derived from tetrafluoroethene and wherein the fiuoropoiymer has a gel content of less than 3,000 / m ^a and

(ii) subjecting the composition to meit-extrusion to obtain an extruded article,

In a further aspect of the present disclosure there is provided a method of making a

tetraf I uoroethe ne-based fiuoropolymer, having an MFI (265/5) of from about 13g/10 min to about 30g/10 min and a melting point between 170°C an 230 ^o C _s wherein the tetrafluoroethene- based fiuoropolymer comprises interpoiymerized units of tetrafluoroethene and ethene or interpoiymerized units of tetrafluoroethene and hexafiuoropropene, and comprises more than 52 % by weight, based on the weight of the fiuoropolymer, of the units derived from

tetrafluoroethene and wherein the fiuoropoiymer has a gel content of less than 3,000/m ^? , said method comprising polymerizing the monomers making up the fiuoropolymer in an aqueous emulsion polymerization using the f!uorinated emulsifier according to the formula <l) wherein Rf is selected from a pariiafiy or fufiy fiuorinated alky! group that may optionaiiy be interrupted with one or more oxygen atoms; L is selected from a partiaiiy or fully fiuorinated Sinear or branched aikylene group that is optionaiiy interrupted with one or more oxygen atoms, and X" represents a cation or H',

and in the presence of one or more fiuorinated liquids selected from saturated partiaiiy or perfiucrinated hydrocarbons which may contain one or more catenary heteroatoms selected from oxygen and/or nitrogen and having a boiling point of greater than 50 ^* C.

Other features and advantages of the invention will be apparent from the following detailed description of the invention and the claims. The above summary of principles of the disclosure is not intended to describe each illustrated embodiment or every implementation of the present disclosure. The following details more particularly exemplify certai preferred embodiments utilizing the principles disclosed herein.

Detested Description

Flu oro polymers

The fiuoropolymers according to the present description are TFE-based copolymers. This means they contain at least 52% by weight based on the weight of the total polymer of units derived from tetrafluoroethene (TFE). The fiuoropolymers are partially fiuorinated, which means they contain at least one partially fiuorinated comonomer and/or at least one non- fiuorinated comonomer. The term "copolymer" in connection with the present invention should generally be understood to mean a polymer comprising repeating units derived from the recited monomers without excluding the option of other further repeating units being present that derive from other monomers not explicitly recited. Accordingly, for example the term "copolymer of monomers A and 8" includes binary polymers of A and B as well as polymers that have further monomers other than A and 8, such as terpoiymers and quad polymers. The copolymers are made up by the units derived from their monomers, i.e. interpoSyme ized units of these monomers. For example, a TFE-E copolymer is prepared by copoiymerizing the monomers TFE and E and thus contains units derived from TFE and E, i.e. interpolymerized units of TFE and E. Examples of suitable TFE-based polymers include copolymers comprising TFE and ethene (TFE-E), TFE, HFP and ethene (HTE). TFE, HFP and VDF (THV).

TFE-E copolymers may comprise from about 10 to about 30% fa weight of units derived from ethene with the remainder being units derived from TFE and optionally on o more further comonomers as described beiow with the proviso that the amount of units derived from TFE is at least 52 % by weight.

HTE copolymers may comprise from about 10 to about 30% by weight of units derived from hexafluoropopene and from about 5 to about 20% by weight of ethene with the remainder being units derived from TFE and optionally one or more further comonomers. as described beiow with the proviso that the amount of units derived from TFE is at least 52 % by weight.

THV copolymers may comprise from about 10 % up to about 40% by weight of units derived from vinyiidenefluoride, from about 10 to about 40 % by weight of units derived from hexafluoropropene and from 0 to about 10% by weight of further comonomers as described herein below with the proviso that the amount of units derived from TFE is at least 52 % fay weight.

The above-described copolymers may or may not contain one or more further comonomers. Such further comonomers preferably are fluorinated olefins, more preferably fSuorinated or perfluorinated alpha-olefins, i.e. olefins with a terminal C-C double bond. Such further comonomers include but are not limited to trichlorofiuoroethene (CTFE), perfluoro vinyl or allyi ethers corresponding to the wherein n is 1 or 0 and Rf represents a perfluorinated aliphatic group that may contain one or more oxygen atoms.

Specific examples of perfluorinated alky! vinyl ethers include perfluoro methyl vinyl ether {PivlV ^' E}, perfluoro ethyl vinyl ether (PEVE), and perfluoro n-propy! vinyl ether (PPVE-I). Specific examples of perfluorinated alkoxy vinyl ethers include peril uoro-2~propoxy propyl vinyl ether {PPVE-2}, perfluoro-S-rnethOxy-n-propylvinyl ether (MV-31 ), perfiuoro-2-mefhQxy-ethyivinyS ether and CF3-{CF ₂ ) ₂ -O-CF(CF ₃ )-CF ₂ -0-CF{CFa}-CF ₂ -0-CF-CF ₂ (PPVE~3). Some of the aforementioned perfluoro vinyl ethers wi be liquid under th conditions of polymerization and are thus non-gaseous fluorinated monomers. Typically, the co-monomers, however, do not contain more than 1 , preferably no more than 1 1 , most preferably not more than 8 carbon atoms.

The TFE-based copolymers according to the present description are melt-processab!e. In connection with the present description, a fiuoropoiymer is considered to be rneit-processabie if the melt viscosity of the polymer is low enough such that the polymer can be processed in conventional extrusion equipment used to extrude polymers. Therefore, melt-processable fluoropolymers typicaliy have a melt flow index {MFi) at 265°C and a 5 kg load {"MFi 265/5") of at least 1 g/ 10 min. This typicaliy corresponds to a me!t viscosit at the processing temperature (e.g. 250 to 400°C) of no more than 10 ⁶ Pa*s, preferably 10* to 10 ⁵ Pa*s, The copolymers according to this description have a meit flow index (MFI) at 265 *C and a 5 kg load ("SV1FI 265/5") of from about 3 to about 30 g/10 min, preferabl from about 13 to about 17 g/10 min. The MFi can be determined, for example, according to AST D-1238. The TFE-based copolymers according to the present description have a me!iing point of at least about 170X. Typically, they have a melting point within the temperature interval of from about 170X up to about 230 .

Typically, the molecular weight distribution ( WD) of the TFE-based copolymers according to the present description is relatively narrow (typically Mw/Mn is from 1.4 to 2.0 or from 1 .5 io 1,9) compared to other technical polymers where the fvw/Mn ratio is about 2.5. The MWD can be determined experimentally, for example by the methods described herein. The MWD can be theoretically predicted according to Hintzer and Loehr, in Modern Fluoropolymers, John Schesrs (editor), John Wiley & Sons, 1997, pages 229 to 230.

The fluoropolymers according to the present description do not have so-called long chain branches or only insignificantly amounts thereof. That is, the polymers are linear or substantially linear, in that only branches are present that are introduced to the polymer backbone by the monomers used. Long chain branches are Introduced into the backbone by using specific branching modifiers in the polymerization. Such modifiers are either bisolefins and/or monooiefins containing iodine and/or bromine atoms. Without intending to be bound by theory, it is believed that long chain branches result from abstraction of the bromine or iodine atom from the modifier once it is polymerized into the backbone of the fluoropolymer. The so-produced radical on th backbone may then cause further polymerization with the result that a polymeric chain is formed as a branch on the backbone. Such branches are known in the art as long chain

Therefore, the fluoropolymers according to the present description are available by a polymerization carried out essentially in absence of any branching modifiers. This means no branching modifiers are present or they are only present in insignificant amount, i.e. in amounts of up to about 0,01% by weight based on total amount of polymer to be produced.

Branching modifiers include polyoiefins or bisolefins or olefins that have on at least one carbon of the double bond a bromine or iodine atom. The olefin may, apart from containing Br and/or I atoms, be norvfluorlnated, i.e. not contain fluorine atoms; may be partially fiuorinated, i.e. some but not all hydrogen atoms have been replaced with fluorine atoms; or the olefin may be a perfluorinate compound in which all hydrogen atoms have been replaced with fluorine atoms except for those replaced with I or Br. Branching modifiers can be represented by the genera! formula:

wherein each X may be the same or different and is selected from the group consisting of hydrogen, F, CI, Br and I, with the proviso that at least one X represents Br or I, 2 represents hydrogen, F, CL Br, I, a perfluoroalky! group, a perfluoroa!koxy group or a perfluoropolyether group.

The level of branching can be determined by the Long Chain Branching Index (LCBI). The IGBS can be determined as described in R, H. Shroff, H. Mavridis; acromoL, 32, 8464- 8464 (1999) & 34, 7362-7367 {2001} according to the equation: and as described in international patent application WO2004/1 124 to Amos et ai.

The LCSI of substantially linear fiuoropolymers is less than 0.2. Therefore, the f!uoropoiymers according to the present description have an LGBi of less than 0,2.

If a fluoropolymer is insoluble in any organic solvent, the level of branching or non- iineariiy can alternativeSy be characterized ihrough the relaxation exponent n (also referred to as "critical relaxation exponent"). As disclosed in WO 2004/094491 , the critical relaxation exponent n of a substantially linear fluoropolymer is greater than 0.90. The lower the exponent, the more branches are present.

To generate long chain branches the amount of the modifier needed will be from 0.01% by weight, or even from 0.05%, and u to 0.25% by weight, even up to 0.4% by weight, or higher based on the total weight of polymer to be produced. Amounts of modifier lower than 0.01 % by weight may not be detrimental in the polymerization if substantially linear polymers are to be prepared but, preferably, no modifier is used at all.

The fiuoropolymers described herein can be made through an aqueous emulsion polymerization process in the presence of a fiuorinated liquid as described, for example, in US patent application No. 2004/0072977 to Kau!bach and Mayer, incorporated herein by reference, but with using the fiuorinated liquids and fiuorinated polyefher surfactants as described herein. As shown in the example section provided herein it has been found that TFE-based

fiuoropolymers having high melting points made with perfluorinated aeids as emuisifiers have an increased gel content. Without being bound by theory it is believed that the combination of the emuisifiers described herein and the fiuorinated liquids described herein used in the

polymerization allows for the production of high melting, melt-processab!e TFE-based poiymers of narrow molecular weight distribution with reduced formation of coagulates during the polymerization. It is believed that this reduced amount of coagulates formed during the polymerization and (incorporated into the isolated po!ymer) may play an important role in the improved optical quality, e.g. the iow gel content, of the fiuoropolymers according to this description. The fiuoropolymers according to the present disclosure typically have a gel content of less than 3,000 /m ² (three thousands/m ² ), preferably less than 1500/ m* (one thousand five hundred/m ² ), most preferably iess than 800/trr' (elghthundred/m ² ). The gel content can be determined by extruding the polymer info a 100 pm thick sheet. The polymers are transparent or opaque at such thickness and internal defects are visible to the naked eye and can be counted to determine the gel content. For aqueous emulsion polymerization, the reactor vessel for use in the aqueous emulsion polymerization process is typically a pressurizab!e vessel capabfe of withstanding the internal pressures during the polymerization reaction, Typically, the reaction vessel will include at least one mechanical agitator, which will produce thorough mixing of the reactor contents and heat exchange system. Any quantity of the fluoromonomer{s) may be charged to the reactor vessel. The monomers may be charged batch-wise or in a continuous or semi-continuous manner. The independent rate at which the monomers are added to the kettle will depend on the consumption rate of the particular monomer with time. Preferably, the rate of addition of monomer will equal the rate of consumption of monomer, i.e. conversion of monomer into polymer. The aqueous emulsion polymerization reaction kettle may be charged with water, the amounts of which are not critical, to provide an aqueous phase. To the aqueous phase is generally also added the fluorinated polyether surfactant described be!ow. At least a part of the fluorinated polyether surfactants is added to the reaction mixture as an aqueous mixture with at least one fluorinated liquid as described below.

Fluorinated polyether surfactants

The fluorinated surfactant is typically used in amounts of about 0.01% by weight to about 1% by weight based on the aqueous phase of the polymerization system. Fluorinated polyether surfactants include those according to general formula:

wherein Rf is selected from a partially fluorinated alkyl group, a fully fluorinated alkyl group, a partiall fluorinated alky! group that is interrupted with one or more oxygen atoms, and a fully fluorinated alkyl group that is interrupted with one or more oxygen atoms, wherein R _f may be linear or branched; L is selected from a partially fluorinated alky!ene group, a fully fluorinated aikylene group, a partially fluorinated aikylene group that is interrupted with one or more oxygen atoms, and a fully fluorinated alkyiene group that is interrupted with one or more oxygen atoms; X ^* represents a cation or H'. L may be branched but preferably L is linear. More preferably, both L and Rf are linear. Preferably either Rf or L or both contain a partially fluorinated group.

Fully fluorinated (or ^■ perfluorinated) alkyiene groups include aikylene groups that consist of only carbon and fiuorine atoms whereas partially fluorinated aikylene groups may additionally contain hydrogen. Generally, a partially fluorinated alkyiene group should not contain more than 2 hydrogen atoms so as to be highly fluorinated and non-telogenic or at least have minimal te!ogenic effects. Examples of L include fully fluorinated aikylene groups, like linear

perfluorinated aSky!enes that have from 1 to 6 carbon atoms, for example linea perfluorinated alkyiene groups of 1 , 2. 3, 4 or 5 carbon atoms. Examples of linear partially fluorinated aikylene groups include those that have from 1 to 6 carbon atoms. I a particular embodiment the linear partially fluorinated aikylene linking group L has 1, 2, 3, 4, 5 or 6 carbon atoms and has only 1 or 2 hydrogen atoms. When the partially fluorinated aikylene group has 2 hydrogen atoms, the hydrogen atoms may be attached to the same carbon atom or they can be attached to different carbon atoms. When they are attached to different carbon atoms, such carbon atoms can be adjacent to each other or not. Aiso, in a particular embodiment, a carbon atom having 1 or 2 hydrogen atoms may be adjacent the ether oxygen atom to which the linking group is attached or adjacent the carboxylic group to which the Sinking group is attached at its other end.

Particular examples of Sinking groups L may be selected from the following:

~(CF ₂ )g- wherein g is 1 « 2, 3, 4, 5 or 6;

-CFH-(Cf ₂ ) _;i - wherein h is 0, 1 , 2, 3, 4 or 5;

-CF.rCFH-(CF ₅ ) _d - wherein d is 0, 1 , 2, 3 or 4;

-CHHCF ₂ ) _n - wherein h is 1 , 2, 3 or 4;

-(CH ₂ ) _C - wherein c is 1 , 2, 3 or 4.

in the above examples, the ieft side of the formula of the Sinking group is the site where the iinking group is connected to an ether oxygen in formula (I), Preferabiy Rf is perfluorinated when L is partially fluorinated and vice versa.

The Rf group in formula (I) represents a partially fiuorinated aikyi group, a fully fluorinated alkyl group, a partially fiuorinated aikyi group that is interrupted with one or more oxygen atoms, and a fuiiy fluorinated aikyi group that is interrupted with one or more oxygen atoms. In one embodiment, Rf is a linear perfluorinated aliphatic group having 1 to 6 carbon atoms, preferably having 1 , 2, 3 or 4 carbon atoms. According to another embodiment Rf is a linear perfiuorinated aliphatic group interrupted with one or more oxygen atoms of which the aikyiene groups between oxygen atoms have not more than 4 or 6 carbon atoms, for example 3 or less carbon atoms and wherein the terminal aikyi group has not more than 4 or 8 carbon atoms, for example 3 or less carbon atoms.

According to a further embodiment, Rf is a linear partially fluorinated aliphatic group having 1 to 8 carbon atoms and not more than 2 hydrogen atoms or a linear partially fluorinated aliphatic group interrupted with one or more oxygen atoms and which has not more than 2 hydrogen atoms, Sn the latter embodiment, it will generally be preferred that any perfluorinated aikyiene moiety has not more than 4 or 6 carbon atoms a d any terminal perfluorinated alkyl group likewise preferably should not have more than 6 carbon atoms, for example not more than 4 carbon atoms. A particular example of a partially fluorinated aliphatic group Rf is CF _:i CFH-.

The anion part of formula (!) shall have a molecular weight of less than 1 ,500 g/moie. preferabiy less than 998 g/mole.

Specific examples of compounds according to formula (I) include, but are not limited to, the following: a) Rf-O-CHF-COOX; b) Rf-0-CHF-CF ₂ -COOX; c) Rf-0-CF _r CHFCOOX; d) Rf-0-CF CHF-CFzCOOX; e) Rf~(0}m~CHF-Cf _a -0-(CH ₂ )n~COOX n=1 , 2 or 3; m^G or ; f) Rf-0-((CFj) _n - G) _m ~CH COOX n=1 , 2, or 3; m~Q, 1 , 2; g) Rf~0-(CF ₂ )G-COOX (wherein Rf is partially fluorinated), X has the meaning as described above. Specific examples include, but are not limited to: a) Rf-O-CHF-COOX:

CsFrO-CHF-COOX

CF _r O-CF ₂ CF CF ₂ -0-CHF-COOX

CF ₃ CF ₂ CF ₂ -Q~CF ₂ CF ₂ -CF _£ -G~CHF-CQOX

CF ₃ ~0-CF _z -CF ₂ -0-CHF-COOX

CFs-O-CFrO-CFrCF O-CHF-COOX

CF ₃ -{OeF ₂ ) ₂ ~Q-CF _r CF O-CHF~COOX

b) Rf-O-CHF-CFrCOOX:

CF O-CHF-CF ₂ -CQOX

CF ₃ ~G-CF ₂ CF ₂ -0-CHF-CF ₂ ~COOX

CF ₃ -CF O-CHF-CF ₂ -COOX

CF;rO-CF ₂ CFrCF ₂ ~0-CHF-CF ₂ -COOX

CF, O-CF O-CF ₂ GF O-CHF-CF COOX

CF ₃ -(OCF _s ) ₂ -0-CF ₂ CF ₂ -0-CHF-CF ₂ -COOX

CFr(OCF ₂ )3-0~CF ₂ CF ₂ -D-CHF-CF _a -COOX c) Rf-0-CF _? -CHFCOOX:

CF ₃ -0-CF;rCHF-COOX

CaFrG-CFs-CHF-COOX

CF ₃ -0-CF ₂ CF ₂ CF ₂ -0-CF ₂ -CHF-COOX

CF O.CF O-CF ₂ CF ₂ -0-CF ₂ -CHF~COOX

CFr(OCF ₂ } ₂ -0-CF ₂ CF ₂ -0"CF ₂ -CHf-COOX

CFr{OCF ₂ ) ₃ -Q-CF ₂ CF _£ -0-CFrCHF-COOX d) f-O-CFrCHF-CF ₂ C00X:

CF ₃ -0-CF ₂ -CHF-CF ₂ ~COO

C ₂ F _s -0-CF ₂ -CHF-CF ₂ -COOX

C ₃ F ₇ -0-CF ₂ -CHF-CF COOX

CF O-CF ₂ CF ₂ CF ₂ -0~CF ₂ -CHF-CF ₂ -COOX

CF ₃ ~O-CF 0-CF ₂ CF ₂ -0-CF _z -CHF-CF ₂ -COOX

CF ₃ -(OCF ₂ ) ₂ -0-CF ₂ CFrO~CF CHF-CF ₂ -COOX

CF ₃ -(OCF ₂ ) _? .~0-CF ₂ CF ₂ -0-CF _; .-CHF-CF ₂ -COOX e) Rf-(0)m-CHF-CF O-iCH ₂ )n-COOX n- 1 , 2 or 3; m~0 or 1 CF ₃ -0-CHF-CF _r O-CH COOX

CF ₃ -0-CF ₂ CF ₂ CF ₂ -0-CHF-CF ₂ "0-CH;rCOOX C ₃ F O~CHF-CF ₂ -0-CH COOX

C ₃ Fr-0-CHF-CF ₂ -0-CH ₂ CH ₂ -COOX

C ₃ F ₇ -0-CF ₂ CF O-CHF-GF OCHrCOOX

C ₃ F ₇ -0-CF CF ₂ -GF ₂ -0-CHF.CF ₂ -OCH ₂ -COOX

C ₃ F ₇ -0-CF CHF-CF ₂ -OCH ₂ -COOX

CFs-CHF-CF O-CHa-COOX

C ₃ F ₇ -CF. CHF-CF ₂ -OCH COOX f) Rf-0-((CF ₂ } _n -0) _m -CH ₂ -COOX n~1 , 2, or 3; rrs^O, 1, 2

CF ₃ -0-eF ₂ CF ₂ -Q-CH _a -COOX

CF3.0^CF ₂ CF ₂ CF. O~CF ₂ CF ₂ -0-CH COOX

C ₃ F _? -0-CF ₂ CF O-CH ₂ -COOX

C ₃ F ₇ -0-CF ₂ CF2-0-CF ₂ CF OCH ₂ -COOX

C ₃ FrO-CF ₂ CF ₂ CF ₂ -0-CF ₂ CF ₂ -OCH COOX

C ₃ F ₇ -0-CF ₂ CF ₂ CF ₂ -OCH ₂ -COOX

C,F ₉ -0-CH _;r COOX

C ₃ F _r O-CH ₂ -COGX

C ₅ F ₃ -OCH COOX g) Rf-0-(CF _i; )0-COOX (wherein Rf is partially fluorinated like but not limited to):

CF ₃ CHF-O-(CF ₂ )0-COOX:

CF ₃ CFM-0 iCF ₂ ) ₃ -COQX

CF ₃ CFH-0~{CF ₂ ) ₅ -COOX

CF ₃ CFH-0-{CF ₂ )0-COOX

CF ₃ CFH~0-(CF ₂ 5 COOX

CF ₃ CFH-0-(CF ₂ ) ₅ ~COOX

These surfactants and their preparation have been described, for example, in U $2008/0015304 to Hinlzer et al., incorporated herein by reference. The surfactants are also commercially available from Antes Ltd, St. Petersburg, Russia.

It is understood that while the description of compounds in the present application may reference only the acid form or only the salt form of a certain species, the corresponding acids and salts, in particular the H ⁴ⁱ , potassium, sodium or lithium salts, can equally be used. inert fluorinated liquids

The inert fiuonnated liquid may, for instance, be selected from aliphatic and aromatic fluorinated ethers or polyethers that optionally may have (but preferably have not) sulfur and/or nitrogen atoms. The fluorinated liquid typically will have a boiling point of at least 30 ^C C, at least 50*C, at least 100°C, or even at least 150°C, for example between 150°C and 230X. Fluorinafed liquids with boiling points above 230°C are also contemplated. For instance, fluonnated liquids may have boiling points up to 250 ^* 0, up to 3Q0°C, even up to 350°C.

The fiuorinated liquid preferably is a partially fluonnated liquid. Preferably, the partiall fiuorinated liquid contains only one or two or three hydrogen atoms, it is preferred, however, that a partially fluorinafed liquid does not act as a chain transfer agent in the aqueous phase. Chain transfer agents are non-radicai species that react with a radical species. This may involve, for instance, a chain transfer agent reacting with an actively polymerizing chain. The result of this reaction is at least one different radical species. After this happens, the polymerizing chain is terminated. A new chain may or may not start, depending on the reactivity of the new radical species, in many cases, the result is a diminution of the molecular weight of the resulting polymer compared with a polymer prepared under the same conditions except that the chain transfer agent is not present. This diminution of moiecuiar weight often takes place without a change in the overall rate of conversion of monomer to polymer. Therefore, it is possible to determine whether a fiuorinated liquid is acting as a chain transfer agent in the aqueous phase by observing the moiecuiar weight of the resulting polymer with and without the fiuorinated liquid. If the molecular weight is significantly decreased with the addition of the fiuorinated iiquid (e.g., by 10% or more, by 20% or more, or even by 30% or more}, then the fiuorinated iiquid is acting as a chain transfer agent in the aqueous phase. Particular embodiments of fiuorinated liquids include those selected from fiuorinated polyethers of the formula:

Rf-X-0~Rf1 00

wherein Rf is selected from partially fiuorinated, preferably perfluorinated, aikyi groups having from 1 to 4 carbon atoms, and n is from 1 to 10; X is an aikylene oxy or poiyoxya!kyiene unit having from 1 to 10 carbon atoms; Rf1 is selected from CH ₃ , or a partially fiuorinated or perfluorinated alkyl grou having from 1 to 10 carbon atoms. Preferably, the ether is partially fiuorinated and either Rf or Rfl or both are partially fiuorinated. Specific examples include compounds according to the general formula:

Rf- C ₃ F _e ]n~0-CHFCF ₃ (HI) wherein Rf is selected from or partially fiuorinated, preferably a perfluorinated, aikyi group having from 1 to 4 carbon atoms, and n is from 1 to 10; and

Rf'-O-CFH-CFs-O-R (IV) wherein Rf may be selected from a perfluorinated aikyi group having from: 1 to 10 carbon atoms and R may be selected from CH ₃ and Rf, wherein when R is Rf, it may be the same or different than the other Rf.

Particular embodiments according to formula (if) include perfluoropolyethers of formula: Rf ^, ~(OCF ₂ )x-{OCF ₂ CF ₂ }y-(CF(CF ₃ )-CF ₂ )z-(OCF{CF ₃ ))a-Q

In formula (Ha) Rf" is selected from partially or perfluonnated aikyl groups having from 1 to 10 carbon atoms; Q is selected from Rf and Rf ^> -(OCF _i )x-(OCF ₂ CF ₂ )y-(CF(CF _d )-CF ₂ )z- {OCF(CF ₃ ))a; each x, y. z, and a is independently selected from 0 to 10, with the proviso that the sum of x+y+z+a is at least 1 .

In yet other embodiments, fiuorinated liquids include perfluonnated Hydrocarbons such as, for instance, perfluorinated saturated aliphatic compounds such as a perfluorinated aikanes; peril uorinated aromatic compounds such as perf!uorinated benzene, or perftuorinated tetradecahydrophenanthene. Perfluorinated liquids also include perfiuorinated aikyl amines such as a perfluorinated trialkyi amine. Furthermore, the perfiuorinated liquid may be a perfiuorinated cyclic aliphatic compounds, such as decalin. and preferably a heterocyclic aliphatic compound containing oxygen, nitrogen or sulfur in the ring, such as perfiuorinated N-aikyi substituted morpho!ines or perfiuoro-2-butyi tetrahydrofuran. Specific examples of perfiuorinated

hydrocarbons include perfluoro-2~butyitetrahydrofuran, perfluorodecaiin, perfluoromethyldecalin, perfluoromethyidecaiin, perfluoromethyfcyclohexane, perfiuoro{1 ,3-dimethylcyclohexane), perf!uorodlmethyldecahydronaphtha!ene, perfluoro{tetradecahydrophenanthrene),

perfluorotetradosane, perfiuorokerosenes, oligomers of poiy(chlorotrifluoroethylene).

perf!uOiO{trialkylamine} such as perfluoro{tripropyiamine), perfluoro{tributyiamine), or

perfluoro{tripentylamine), and octafiuorotoluene, hexafiuorobenzene, and commercial fiuorinated solvents, such as F!uorineri FC-75, FC-72, FC-84, FC-77, FC-40, FC-43, FC-70 or FC 5312 all available from 3M Company, Saint Paul, Minn, The fiuorinated aikanes can be linear or branched, and typically have a carbon atom number between 3 and 20.

Th total amount of fiuorinated liquid may be not more than 1% by weight based on the weight of the aqueous phase. Typically, the fiuorinated po!yether surfactant is at least partially added to ih© polymerization medium as an aqueous mixture, preferably an emulsion or microemuision, containing one or more fiuorinated liquids as described above. Stable emulsions do not show phase separation within 8 hours after stirring has ceased. This mixture may contain a partial or the entire amount of fiuorinated liquids used in the polymerization.

The gaseous or liquid fiuorinated monomers are polymerized in the appropriate amounts and ratios to give the TFE-base copolymers described herein.

The polymerization is usually initiated after an initial charge of monomer by adding a radical initiator or Initiator system to the aqueous phase. For example, peroxides can be used as free radical initiators. Specific examples of peroxide initiators include, hydrogen peroxide, diacy!peroxides such as diacetylperoxide, dipropionylperoxide, dibutyry I peroxide,

dibenzoyiperoxide, benzoyl acetyiperoxide, dig!utaric acid peroxide and diiaurylperoxide, and further water soluble per-acids and water soluble salts thereof such as e.g. ammonium, sodium or potassium salts. Examples of per-acids include peracetic acid. Esters of the peracid can be used as well and examples thereof include tertiary- butyl eroxyacetate and tertiary- butylperoxypivalate. A further class of initiators that can be used are water soluble azo- compounds. Suitable redox systems for use as initiators include for example a combination of peroxodisulphate and hydrogen sulphite or disuiphite, a combination of thiosulphate and peroxodisulphate or a combination of peroxodisulphate and hydrazine. Further initiators that can be used are ammonium- alkali- or earth alkali salts of persulfates, permanganic or manganic acid or manganic acids. The amount of initiator employed is typically between 0.003 and 2 % by weight, preferably between 0.005 and 1 % by weight based on the total weight of the polymerization mixture. The full amount of initiator may be added at the start of the

polymerization or the initiator can be added to the polymerization in a continuous way during the polymerization until a conversion of 70 to 80% of the fed monomers is reached. One can also add part of the initiator at the start and the remainder in one or separate additional portions during the polymerization. Accelerators such as for example water-soluble salts of iron, copper and silver may also be added. During the initiation of the polymerization reaction, the sealed reactor kettle and its contents are conveniently pre-heated to the reaction temperature,

Po!ymenzatton temperatures may be from 20°C, from 30°C, or even from 40°C and may further be up to iOO'C, up to 120.'C, or even up to 150°C. The polymerization pressure may range, for instance, from 4 to 30 bar, in particular from 8 to 20 bar. The aqueous emulsion polymerization system may further comprise auxiliaries, such as buffers and complex-formers.

A chain transfer agent may be charged to the reaction kettle to control the molecular weight distribution. The chain transfer agent may be added, for example, prior to the initiation of the polymerization. Useful chain transfer agents include C2 to C1Q hydrocarbons such as ethane, alcohols, ethers, esters including aliphatic carboxyiic acid esters and maionic esters, ketones and haiocarbons. Particulariy useful chain transfer agents are dialkylethers such as dimethyl ether and methyl tertiary butyi ether. Further additions of chain transfer agent in a continuous or semi-continuous way during the polymerization may also be carried out. For example, a fluoropolymer having a bimodal molecular weight distribution is conveniently prepared by first polymerizing fluorinated monomer in the presence of an initial amount of chain transfer agent and then adding at a later point in the polymerization further chain transfer agent together with additional monomer.

The amount of polymer solids that can be obtained at the end of the polymerization is typically at ieast 10% by weight, or even at least 20% by weight, and up to 40% by weight, and even up to 45% by weight; and the average particle size of the resulting fluoropolymer is typically between 50 nm and 500 nm.

The dispersion may be purified to remove fluorinated surfactants by ion exchange as known in the art, for example as described in EP 1 ,155,055 A1. The polymers can be isolated by coaguiaiion, for example by physical coagulation (freezing), mechanical coaguiaiion (increased shear force) or salt-induced coagulation as known in the art.

The fluoropolymers according to the present description can be processed by meit extrusion to create an extrusion product. Melt extrusion processes include feeding of the polymer in its molten form through a die. Typically, the geometry of the die determines the shape of the extruded product. Melt extrusion processes include for instance, meit spinning, wire and cable extrusion, blown film, hose extrusion, film extrusion, tube extrusion, and blow- molding of hollow bodies.

Typically, the extrusion product may be a meit pellet to convert the polymer into a form that is easier to transport and store. Meit pellets typically are granules obtained by melt extruding the polymer into a strand and cutting the strand into smaller pieces. Meit pellets are typically of cylindrical shape and typically have a diameter and/or a length of at least 0.5 cm. Typically, melt pellets may have diameter or a length of from about 0.2 to 10 cm or from about 1 to 5 cm.

The fluoropolymers according to the present description (including the fluoropolymers in the form of a melt pellet) are particularly suitabl for film extrusion, for example in the preparation of sheets. Sheets are rectangular articles having a length and width and a thickness. The length is the greatest dimension of the sheet followed by its width and its thickness, The width and thickness of an extruded sheet Is determined by the dimensions of the extrusion die. The fiuoropoSymers provided herein can be extruded by standard film extrusion equipment into a sheet. The extrusion product may be a single sheet or a multi-layer article, in which case the extrusion process may involve coextrusion of another fiuoropoiymer or a non fiuorinated polymer. Extruded fiuoropoiymer films may have a thickness of from about 10 pm to about 3,000 pm or from about 30 pm to about 5,000 pm.

Prior to melt extrusion, in particular prior to film extrusion the fluoropolymers according to the present description may be blended with fillers or other additives to create a fiuoropoiymer composition. Such fiuoropoiymer compositions may contain the fiuoropoiymer as described herein, in any relative amount, for instance, the presence of fiuoropoiymer may be in at least 90% by weight based on the total weight of the composition, at least 50%, at least 20% by weight. Fiuoropoiymer compositions may contain additives, like for example, organic or inorganic fillers, such as carbon particles, hollow glass particles (for example available under the trade designation GLASS BUBBLES from 3IV1 Company), solid glass particles, silica, clays; pigments (for example zinc oxide, zinc sulfide, titanium dioxide), reinforcing agents (for example fibers, like glass fibers or carbon fibers) and antioxidants, lubricants, acid scavengers and other know additives used in the art.

The term melt-extrusion product is used herein to denote both, the fluoropolymers and the fiuoropoiymer compositions according to the present description. In some embodiments, the extrusion products described herein may be useful for backside films in photovoltaic modules, for frontside films for flexible photovoltaic modules, and/or for blown films for decorative applications, such as decorative films applied in the fuselage of aircraft, for films in architectural applications, for example on buildings or green houses, in a particular embodiments the f!uorapolymers or fluoropolymer compositions may be melt extruded to form films, preferably films in a multilayer article, for example multilayer laminates. In case of multilayer productions, the fluoropolymers may be coextruded with one or more other polymers to form the multilayer article or laminated to another Iayer or attached to another iayer by using an adhesive. Multilayer articles, for example multilayer films or laminates are constructions, which attempt to marry the properties of dissimilar materials in order to provide an improved performance. Such properties include barrier resistance to elements such as water, cut-through resistance, weathering resistance and/or electrical Insulation.

Multilayer laminates containing fluoropolymers may be used in pipes, tubings, or as protective sheets in solar modules, or green houses, windows or buildings, Such protective sheets, in particular in solar modules, are typically laminates, and typically contain a fluoropolymer layer as an externa! layer and furthers layers of barrier materials such as, but not limited to PET

(polyethylene terepthalate), or may include metal foils or inorganic coatings to provide further functional features like vapor barriers, increased reflection of incoming light and thermal and electrical insulation. These baeksheets may include multiple layers of fluoropolymers or non fluoropolymers. The conventional constructions typically require that the completed, typically multilayer, construction be subjected to a heating cycle pr or to lamination so that the entire construction can be successfully laminated. An advantage of the fluoropolymers and their extrusion products provided herein is that they have a good optical appearance despite having a melting point of greater than 170X, The high melting point allows for applying broader temperature profile in the lamination process. For example, partially fluorinated fluoropolymer sheets having melting points below 170X may soften during standard lamination processes used in the solar module industry, and may lead to undesired adhesio effects.

Typically, the extrusion product comprising the fluoropolymers according to the present description forms an outer layer of the multi-layer article. The Iayer is typically an extruded or coextruded iayer and has a thickness of from about 10 to 500 pm. Greater thicknesses can be also achieved, fo example layers or sheets having a thickness of from about 20 or 50 pm to 1 ,000 μηι or 5,000 μητι. The fluoropolymer layer preferably has a tensile modulus of less than 99,000 psi, as defined in AST D638. The noted tensile modulus is directed to achieving desired flexural characteristics in order to make the finished film structure pliable in its intended application. The multilayer article may typically include an intermediate iayer. The intermediate Iayer having first and second outer layers bonded to opposing sides of the intermediate Iayer. instead of a single intermediate layer also multiple, preferably adjacent or abutting intermediate layers may be used. The intermediate layer typically has a shrinkage rate of less than 1% at 150 ^" C when heid for about 15 minutes. The multilayer film may contain a second outer !ayer. The intermediate layer typically contains an olefinic ester resin, typically a polyester. Polyesters capable of being processed into film form (for example having a thickness of 50 to 5,000 μ-m) may be suitable as an intermediate layer. These may include, but are not limited to,

homopolymers and copolymers from the following families: polyesters, such as polyethylene terephthalates (PET), and ethylene vinylacetates (EVA), in alternative embodiment, th intermediate may include other poiymers such, for example; poiyacryiates; poiyamides, such as polyamide 6, polyamide 11, polyamide 12, polyamide 46, polyamide 66, polyamide 69, polyamide 610, and polyamide 612; aromatic poiyamides and polyphthalamides; thermoplastic polyimtdes; po!yetherimides; polycarbonates, such as the polycarbonate of bisphenoi A; acrylic and methacrylic polymers such as polymethyl methacrylate; chlorinated poiymers, such as polyvinyl chloride and poiyviny!idene chloride; poSyketones, such as poly{aryl ether ether ketone) (PEEK) and the alternating copolymers of ethylene or propylene with carbon monoxide; polystyrenes of any tacticity, and ring- or chain-substituted polystyrenes; poly ethers, such as polyphenylene oxide, poSy(dimethylphenytene oxide), polyethylene oxide and poiyoxymethylene; ce!lulosics, such as the cellulose acetates; and sulfur-containing poiymers such as

polyphenylene sulfide, polysuifones, and poiyethersuifones, A most preferred material is polyethyieneterepthalate.

The second outer layer may comprise a resin other than the fluoropofymers according to the present description. Preferably, such resins are olefinic polymers. Olefinic poiymers usefui in the composition of multi-layer articles Include polymers and copolymers derived from one or more olefinic monomers of the general formula CH2=CH ", wherein R" is. hydrogen or 01-18 alky!. Examples of such olefinic monomers include propene, ethene, and 1-butene, with ethene being generall preferred. Representative examples of polyolefins derived from such olefinic monomers include polyethene (like but not limited to HOPE, LDPE, LLDPE, UHWPE), polypropene, polybutene-1 , poly{3-methylbutene), pofy(4-methylpentene) and copolymers of ethene with propene, 1-butene, i-hexene, 1- octene, 1-decene, 4-methyl-i-pentene, and 1- ocfadecene.- The olefinic polymers may optionally comprise a copolymer derived from an olefinic monomer and one or more further comonomers that are copolymerizable with the olefinic monomer. These comonomers can be present in the poly olefin in an amount in the range from about 1 to 10 wt-% based on the total weight of the polyolefin, Useful such comonomers include, for example, vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl faufyrate, vinyl chloroacetate, vinyl chloropropionate; acrylic and alpha- aikyi acrylic acid monomers, and their alkyi esters, amides, and nitriies such as acrylic acid, methacrylic acid, efhacrylic acid, methyl aery late, ethyl acrylate, N.Ndimethyi acryiamide. methacrylamide, acrylonitrile; vinyl aryi monomers such as sfyrene, o-methoxystyrene, p-methoxystyrene, and vinyl naphthalene; vinyl and vinyiidene haiide monomers such as viny! chloride, vinyiidene chloride, and vinyiidene bromide; a!kyl ester monomers of rnaleic and fumaric acid such as dimethyl maleate, and diethyl maleate, vinyl alkyl ether monomers such as vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether, and 2-chSoroethyl vinyl ether; vinyl pyridine monomers; N- vinyl carbazo!e monomers, and N-vinyS pyrrolidine monomers.

The second out layer may be an encapsulating layer. This means the layer comprises a resin that is cross-linkable. Cross-linking may be achieved thermally, or physically by which is meant irradiation treatment with x-. β- o v- beams, like but not limited to e-beam; or light, like for example i or UV irradiation. Preferably the resin is flowabte or melts at a temperature greater than 80°C and below the melting point of the TFE-based fiuoropolymer according to the present description. Suitable encapsulants include the o!efinic polymers described above and in particular ethene vinyl acetates (EVA), polyeihene (PE) and po!ypropene (PP) but also silicones.

The first and/or second outer layer and/or the intermediate layers may contain conventional adjuvants such as antioxidants, light stabilizers, acid neutralizers, fillers, antiblocking agents, pigments, primers and other adhesion promoting agents.

Optionally, one or more layers in a multilayer article may also include known adjuvants such as antioxidants, light stabilizers, conductive materials, carbon black, graphite, fillers, lubricants, pigments, plasticizers, processing aids, stabilizers, and the like including

combinations of such materials. In addition, metallized coatings and reinforcing materials also may be used. These include, e.g. , polymeric or fiberglass scrim that can be bonded, woven or nan- woven. Such a material optionally may be used as a separate layer or included within a layer in a muifi-fayer embodiment according to t e present disclosure.

To be most useful, the multilayer articles of the present disclosure should not delaminate during use. That is, the adhesive bond strength between the different layers of the multi-layer article should be sufficiently strong and stable so as to prevent the different layers from separating on exposure to, for example, moisture, heat, cold, wind, chemicals and or other environmental exposure. The adhesion may be re uired between non- fiuoropolymer layers or adjacent the fiuoropolymer layer. Various methods of increasing interlayer adhesion in ail cases are generally known by those of skill in the art. The article of the invention may also include a bonding interface or agent between said outer and intermediate layers. A variety of methods have been employed to bond polymeric materials comprising a fiuoropolymer to substantially non- fiuorinated polymeric materials. For example, the layers can be adhesively bonded together by a layer of adhesive material between the two layers. Alternatively, surface treatment of one or both of the layers, used independently or in conjunction with adhesive materials, has been used to bond the two types of materials together. For example, layers comprising a fiuoropolymer have been treated with a charged gaseous atmosphere followed by lamination with a layer of a noR-iluorinated polymer. As another approach, "tie-!ayers" have been used to bond a fluoropo!ymer material to a layer of materia! comprising a substantially non-fiuorinaied polymer.

One specific surface treatment of a fluoropolymer for improving adhesion is disclosed in U.S. Pat. No. 8,630,047, herein incorporated by reference in its entirety, The specific surface treatment involves the use of actinic radiation, such as ultraviolet radiation in combination with a light-absorbing compound and an electron donor, in a preferred embodiment, one such tie layer method for improving inter!ayer adhesion with the fluoropolymer comprises blending a base and an aromatic material such as a catechol novolak resin, a catechol cresol novolak resin, a po!yhydroxy aromatic resin (optionally with a phase transfer catalyst) with the fluoropolymer and then applying to either layer prior to bonding. Alternatively, this composition may be used as the fluoropolymer layer without separate tie layer as disclosed in U.S. Published Application No. 2005/0080210 A1, herein Incorporated by reference in its entirety.

Another tie iayer method for bonding fluoro polymers is the use of a combination of a base, a crown ether and a non-fluoropolymer. This method is disclosed in U.S. Pat. No. 6,767,948, herein incorporated by reference in its entirety,

Another method thai may be used as a tie Iayer or as a primer for bonding fluoropo!ymers involves the use of an amino substituted organosilane, The method is fully disclosed in U.S. Pat. No 6753,087, herein Incorporated by reference in its entirety. The organosi!ane may optionally be blended with a functionalized polymer. Adhesion between non-f!uoropolymer layers may aiso be accomplished in a variety of ways including the application of anhydride or add modified poly olefins, the application of silane primers, utilization of electron beam radiation, utilization of ultraviolet light and heat, or combinations thereof.

In a preferred embodiment, the intermediate layer and the second outer layer may be combined such as those commercially .available as 3M (TM) Scotchpak (T ) Heat Seaiab!e Polyester Films which include PET films combined with olefinic polymers such as polyester and ethylene vinyl acetate.

Those of ordinary skill in the art are capable of matching the appropriate the conventional bonding techniques to the selected multilayer materials to achieve the desired level of interiayer adhesion.

The multi-layer articles of the invention can be prepared by several different methods. For instance, one process for preparing a multilayer article featuring a fluoropolymer iayer of the present description involves extruding one layer through a die to form a length of film. A second extruder supplies a die to coat another layer of molten polymer onto a surface of the first film. Additional layers can be added through similar means. Alternatively, the polymeric resins of two or more substituent layers may be GO- extruded through a multi-manlfoid die to yield an intermediate or final product. Those skilled in the art of coating technology are capable of selecting process equipment and processing conditions to address selected materials and thereby produce the desired multilayer film.

Following the extrusion operations, the multi-layer article may be cooled, e.g., by immersion in a cooling bath. This process can be used to form multilayer sheets of the invention. In addition, the layers are preferably pressed together, such as through a nip or platen or other known means, Generally, increasing the time, temperature, and/or pressure can improve inter!ayer adhesion. The conditions for bonding any two layers can be optimized through routine experimentation,

Yet another useful method is to pre-form the individual film layers and then contact them in a process such as thermal lamination in order to form a finished article of the invention. The inter-layer adhesion promoting agents, if required, can be applied either sequentially, simultaneously or in-situ with any of the before described processes.

The intermediate iayer, prior to application of the outer layers, should have a shrinkage rate of less than 1 % at 15CTC when held for about 15 minutes, as previously indicated. In that regard, it may be necessary to pre-shrink the intermediate iayer before the application of the other outer layers. Even then so, care must be taken with the addition of the outer layers such that inner layer is not overly tensioned or strained which can reintroduce shrinkage into the overall construction. Pre-shrinking of the film after the addition of other layers can become exceedingly difficult especially if one or more of the additional outer layers has a softening or melting point that is within the temperature range required to pre-shrink the intermediate Iayer.

The thickness of the individual layers within the multilayer film can b varied and tailored per the end-use application requirements. In genera! though, the outer layer of fluoropolymer will be from about 15 to 80 pm, preferably 25 to 50 prrs thick; the intermediate layer will be from about 25 to 250 pm, preferable 50 to 100 pm; and the outer poly olefin layer will be from 25 to 500 pm or greater, preferable it is 250 pm or greater.

The thickness of the overall construction is typically between 300 and 500 pm, and in a preferred embodiment, the thickness of the outer poly olefin layer is as thick, preferably twice as thick, or greater than the combined thickness of the intermediate and fluoropolymer layers. The multilayer film of the present disclosure is suitable for various end use applications. For example, the film may be utilized as a backing layer on solar cells structures. The use of the multilayer film in this manner results in a low cost, conformable, readily applied backing.

Various modifications and alterations of this disclosure will become apparent to those skilled in the art without departing from the scope and principles of this invention, and if should be understood that this Invention is not to be unduly limited to the illustrative embodiments set forth hereinabove and hereinbelow.

Percentages as used herein are weight percentages unless specified otherwise and the total weight of the ingredients adds up to 100% weight. ASTM, DI or other norms as referred to herein are used in the most actuai version as of January 1 , 2012. In the following examples are provided to further illustrate the present disclosure without any intention to limit the disclosure to the specific examples provided.

In the following aiso a list of embodiments is provided to further illustrate the present disclosure without, however, any intention to limit the disclosure to the specific embodiments provided in this list. It is to be understood that the terms, formula and definitions used in this list of embodiments are the same as used in the description and can be used interchangeably. Further details provided in the description with respect to a term or formula used in the list of specific embodiments can be used to further describe thai term or formula.

EXAMPLES Methods e!t flow index

The melt flow index (MFI), reported in g 10 min, was measured according to AST D-1238 at a support weight of 5.0 kg. Unless otherwise noted, a temperature of 265X was applied and a standardized extrusion die of 2.1 mm diameter and 8.0 mm length was used. Melting point

Melting peaks of the fluoropolymers were determined according to ASTM 4591 by differentia! scanning caiomeiry (DSC) (using a Perkin-ESmer DSC 7.0 from PerkinE!mer Inc., Wellesiey, MA) under nitrogen flow and a heating rate of 10°C/min. Th indicated melting points relate to the melting peak maximum.

Processing Evaluation

Critical shear rates 7 ^* _{criV l} reported in reciprocal seconds {s ^" ) _} were determined at 285°C according to A ^' ST D-3835-96 (Standard Test Method for Determination of Properties of Polymeric Materials by Means of a Capillary Rheometer). A capillary rheometer mode!

"Rheotester 1000" from GOTTFERT Werkstoff-Prufmaschinen GmbH (Buchen/Germany) was employed for testing. A variety of plunger speeds were used in ascending order (usually starting from 10 s ^"1 and subsequently increasing b factor of 1.4). The melt was extruded through a capillary having the geometry of 1 mm diameter, 30 mm length and 90° entry angie. When constant flow conditions had been reached, which was monitored by a 500 bar pressure sensor, the extruded monofil was taken and visually inspected. The shear rate at which melt fracture was first visually detected was taken as the critical shear rate. The critical shear rate γ° _οη1 typically correlates with the MFI(265/5) according to the following equation: iog fort.] = 1.Q9xlogi 1FS (265/5)] + 0.61

Gel content

The gel content of the polymers can be determined by the number of defects visible to the naked eye after extruding the polymer into a thin film. The thin film is transparent or opaque and defects reflect or deflect the Sight and appear as (more) intransparent areas {typically as dark or black areas or spots). The number of such spots per m ^} of film gives the gel content of the polymer.

The gel content of the f!uoropo!ymers was determined by imaging methods using a Pixargus Profiicontrol PSPM 500 from Pixargus GmbH, Wuerselen, Germany, The imaging software recorded the number of defects having a size (diameter or length or other longest dimension) of from 0.06 mm to 1 ,00 mm.

For determining the gel content the fiuoropo!ymer was extruded (below its critical shear rate to exclude surface defects) into a film having a thickness of 100 and a width of 130 mm and a length of at least 7 m. The extruded film was placed onto the Pixargus Profiicontrol

Scanner and 7 m of the film were scanned with the film moving through the Pixargus

Profiicontrol Scanner at a speed of 4m/min. The measurements from the first 2 meters of the film were discarded. Polydispersity

w/ n ratios were determined by oscillatory shear flow measurements conducted on f!uoropolymer melts using a strain controlled ARES rheometer (3ARES-13; Firmware version 4.04.00) of TA Instruments New Castle, DE) equipped with a FRT 200 transducer with a force range of up to 200 g. Dynamic mechanical data were recorded in nitroge atmosphere in a first frequency sweep experiment at 265'G using the parallel plate geometry with 25 mm diameter plates. The two plates usually had a distance of 1.8 mm from each other. The thermal control of the oven was operated using the sample/tool thermal element. With an applied strain of typicaiiy 5% it was made sure that the measurements were carried out in the linear regime (as appropriate, higher strains of up to 10% were applied, alternatively). Th measurement frequency was varied in a descending order from 100 to 0.1 rad/s. A second frequency sweep experiment was run at a temperature lower than 265°C but at least 25°C higher than the melting peak maximum of the semi-f!uorinated resin {typically 190°C or 220 ^C C). The other experimental conditions were the same as above, with the exception that a strain of typically 2% was applied for the second frequency sweep. The dynamic mechanical data of the first and the second frequency sweep experiments were combined to a dynamic mechanical master curve using the tirne-temperature-superposition (TTS) tool of the orchestrator software {version 7,0.8.13). Two- dimensional least square fitting was applied and 265°C was chosen as reference temperature. From this master curve, the point was determined using the orchestrator software, where the

21 storage modulus G ^' (co) is equal to the loss modulus G ^" (co). This point has the coordinates of the cross over modulus G _c , reported in Pa _: and the cross over frequency, reported in rad/s. The poiydispersity ratios Mw/Mn reported herein were evaluated from the cross over modulus G _c according to the equation:

Mw/Mn ^ 2.38x(10 ⁶ /G _c )° ⁷⁶

Comparative Example 1

A THV polymer was prepared by aqueous emulsion po!ymerization with

perfluorooctanoic acid as emulsifier and no branching modifier according to the general teaching of example 1 of WO2G09/009361 . The polymer had a straight linear chain topography, an F! (265/5) of 7 2 g/10 min, a melting point of 165°C, and Mw/Mn = 1.55.

The isolated polymer was extruded into a film. The extrusion set-up comprised of a 30 mm single screw (screw length 750 mm) extruder (available from Ide GmbH & co. KG,

Osifildern, Germany), a 150 mm film die (available from Breyer, Wuelfrath, Germany) and a 3- roll stack {available from CoSfin GmbH, Ebersberg, Germany). The temperature profile in the extruder tested was 210°C, 240*0, 250X and 255X from Zone 1 to Zone 4, respectively, A filter pack of 1000/500/200 pm was employed. The die temperatures were all set at 250°C. The output was held constant at 8.2 kg for ail experiments by employing a screw speed of 22 rpm. The 3-ro!S stack temperature was maintained at 80°C and a separation between the die and 3~ roll stack of 30 mm was held constant. The elongation line speed was varied between 3.6 m/min and 13 m/min. The film was extruded and wound up and samples were cut directly from the line to make measurements, such that the film was not folded, deformed or compromised in any manner. The extruded film was examined for its gel content according to the method described above. The film had a gel content of 4,250 (four thousand two hundred and fifty) /m ² ,

Comparative Example 2

A THV polymer having a melting point of 189°C, an MF! (265/5) of 10.0 g /10 min and Mw/Mn of 1 .86 was prepared by aqueous emulsion polymerization like in comparative example 1 but with ,8 g diethylmalonate per kg of THV as chain transfer agent. The polymer was extruded into a film as described in comparative example 1 and had a gel content of 8,280 (eight thousand two hundred and sixty)

Example 1

A linear THV polymer with a melting point of 188°C, Mw/Mn of .53 and an MFI (265/5) of 14.6 g/10 min was prepared according to the general teaching of example 10 of US Patent application No, 2004/0072977 to Kaulbach and Mayer by aqueous emulsion polymerization using a fSuorinaied poiyether as described herein as fluorinated liquid and a fiuorinated polyether surfactant as described herein as emulsifier. The poiymer was extruded into a film as described in comparative example 1 and showed a gel content of 4307m ² .

LIST OF ILLUSTRATIVE EMBODIMENTS

1. A tetraf!uoroethene-based fiuoropoiymer, having an FI (285/5) of from about 13 g/10 min to about 30 g/10 min and a melting point between 170°G an 230°C, wherein the

tetrafluoroethene-based polymer is a copolymer selected from copolymers comprising interpolymerized units of tetrafluoroethene and ethene or inierpolymerized units of

tetrafluoroethene and hexafluoropropene, wherein the copoiymer comprises more than 52 % by weight based on the weight of th copolymer of units derived from tetrafluoroethene and wherein the fluoropoiymer has a gel content of iess than 3,000 / m ² .

2. The tetrafluoroethene-based fluoropoiymer of embodiment 1 having an Mw/ n ratio of from about 1.4 up io 1.9.

3. The tetrafiuoroethene-based fiuoropoiymer according to any one of embodiments 1 to 2 wherein the fluoropoiymer is substantially linear. 4. The tetrafluoroethene-based fluoropoiymer according to any one of embodiments 1 to 3 wherein the fluoropoiymer is a TFE-E copoiymer and comprises from about 10 to about 30% by weight of units derived from ethene with the remainder being units derived from TFE and optionally one or more further comonomers with the proviso that the amount of units derived from TFE is at least 52 % by weight.

5. The tetrafluoroethene-based fluoropoiymer according to any one of embodiments 1 to 3 wherein the fiuoropoiymer is an HTE copolymer and comprises from about 10 to about 30% by weight of units derived from hexafluoropopene and from about 5 to about 20% by weight of ethene with the remainder being units derived from TFE and optionally one or more further comonomers with the proviso that the amount of units derived from TFE is at least 52 % by weight.

6. The tetrafluoroethene-based fluoropoiymer according to any one of embodiments 1 to 3 wherein the fluoropoiyme is a THV copoiymer comprising from about 10 % up to about 40% by weight of units derived from vihyii enef!uoride, from about 10 to about 40 % by weight of units derived from hexafluoropropene and from 0 to about 10% by weight of further comonomers with the proviso that the amount of units derived from TFE is at least 52 % by weight. 7. The melt processab!e tetrafiuoroethene-based fluoropolymer according to any one of the preceding embodiments, wherein the fluoropolymer is obtainable by a radical aqueous emulsion polymerization in the presence of one or more fiuorinated ernuisifiers of the general formuia wherein Rf is selected from a partially or fully fiuorinated a!kyl group that may optionally be interrupted with one or more oxygen atoms; L is selected from a partially or fully fiuorinated linear or branched alkylene group that is optionally interrupted with one or more oxygen atoms, and X ^* represents a cation or H ⁺ _«

and one or more fiuorinated liquids selected from saturated partially or perffuorinated

hydrocarbons which may contain one or more catenary heieroatoms selected from oxygen and/or nitrogen and having a boiling point of greater than 50X.

8. The tetrafiuoroethene-based fluoropolymer according to embodiment 7 wherein L in formula (!) is linear.

9. The tetrafiuoroethene-based fluoropolymer copolymer according to embodiments 7 or 8 wherein the anion part of the compound according to formuia (I) has a molecular weight of less than 1 ,500 g/mole.

10. The tetrafiuoroethene-based fluoropolymer according to any one of embodiments 7 to 9 wherein L In formula (!) is partially fiuorinated.

11. The tetrafiuoroethene-based fluoropolymer according to any one of embodiments 7 to 10 wherein the fiuorinated liquid is selected from a perfluorinated hydrocarbon or a fiuorinated

(poSy)elhef according to the formuia:

Rf-X~0-Rf1 (IS)

wherein Rf is selected from or partially fiuorinated or perfluorinated alkyi group having from 1 to 4 carbon atoms, X is an oxyalkyiene or poiyoxyalkyiene unit having from 1 to 10 carbon atoms; Rf1 is selected from CH ₃ , a partially fiuorinated or perfluorinated alkyi group having from 1 to 10 carbon atoms,

12. The melt-processab!e tetrafiuoroethene-based fluoropolymer according to embodiment 11 wherein the fiuorinated liquid is selected from the fiuorinated (poly)ether according to formuia (II) wherein either Rf or Rf 1 or both are partially fiuorinated.

13. A tetrafiuoroethene-based fluoropolymer, having an Fi (265/5) of from about 13 to about 30 g/10 min (AST ), a melting point (ASTM) of greater than about 170X, wherein the tetrafluoroethene-based fiuoropoiymer is a copolymer comprising more than 52 % by weight based on the weight of the poiymer of units derived from tetrafiuoroethene and is seiected from copolymers comprising interpolymerized units of tetrafiuoroethene and ethene or

interpolymerized units of tetrafiuoroethene and hexafiuoropropene, and wherein the

tetrafluoroethene-based fiuoropoiymer is obtainable by a radical aqueous emulsion

polymerization in the presence of one or more fluorinated emulsifiers of the genera! formula

R _f O-L-CO _? ^" X ^÷ (!) wherein Rf is selected from a partially or fully fluorinated aikyi group that may optionally be interrupted with one or more oxygen atoms; L is seiected from a partially or fully fluorinated linear or branched alkylene group that is optionally interrupted with one or more oxygen atoms, and X ^* represents a cation or H ⁺ ,

and one or more fluorinated liquids selected from saturated partially or perftuorinated hydrocarbons which may contain one or more catenary heteroaioms selected from oxygen and/or nitrogen and having a boiling point of greater than 50 ^e C.

14, The fiuoropoiymer according to embodiment 13 wherein the poiymer is selected from copolymers comprising interpolymerized units derived from a) tetrafiuoroethene,

hexafiuoropropene and ethene (HTE) and b) tetrafiuoroethene, hexafiuoropropene and vinyiidene fluoride (THV) and c) tetrafiuoroethene and ethene (TFE-E).

15. The tetrafluoroethene-based fiuoropoiymer according to any one of embodiments 13 or

14 wherein the fiuoropoiymer is a TFE-E copolymer and comprises from about 10 to about 30% by weight of units derived from ethene with the remainder being units derived from TFE and optionally one or more further comonomers with the proviso that the amount of units derived from TFE is at least 52 % by weight.

18, The tetrafluoroethene-based fiuoropoiymer according to any one of embodiments 13 to 5 wherein the fiuoropoiymer is an HTE copolymer and comprises from about 10 to about 30% by weight of units derived from hexafluoropopene and from about 5 to about 20% by weight of ethene with the remainder being units derived from TFE and optionally one or more further comonomers with the proviso that the amount of units derived from TFE is at least 52 % by weight. 7. The tetrafluoroethene-based fiuoropoiymer according to any one of embodiments 13 to 18 wherein the fiuoropoiymer is a THV copolymer comprising from about 10 % up to about 40% by weight of units derived from viny!idenefluoride, from about 10 to about 40 % by weight of units derived from hexafiuoropropene and from 0 to about 10% by weight of further comonomers with the proviso that the amount of units derived from TFE is at least 52 % by weight.

18. The tetrafluoroethene-based fluoropolymer according to any one of embodiments 13 to 17 wherein the f!uoropolymer has an w/Mn ratio of from about 1 ,4 up to 1 ,9 and/or is substantially linear.

19. The tetrafluoroethene-based fluoropolymer according to any one of embodiments 13 to

18 wherein the fluoropolymer has a melting point of from about 170X to about 230°C.

20. The tetrafluoroethene-based fluoropolymer according to any one of embodiments 13 to

19 wherein L in formula (J) is linear.

21. The tetrafluoroethene-based fluoropolymer according to any one of embodiments 13 to 20 wherein the anion part of the compound according to formula (!) has a molecular weight of less tha 1 ,500 g/mo!e.

22. The tetraflLioroethene-based fluoropolymer according to any one of embodiments 13 to

21 wherein the L in formula (!) is partially fluorinated.

23. The tetrafluoroethene-based fluoropolymer according to any one of embodiments 13 to

22 wherein the fluorinated liquid Is selected from a perfiuorinated hydrocarbon, a fluorinated (poiy)ether according to the formula:

RfcXrORft (I!)

wherein Rf is selected from or partially fluorinated or perfiuorinated alky! group having from 1 to 4 carbon atoms, _. X is an oxyalkySene or polyoxya.lky.lehe unit having from 1 to 10 carbon atoms; Rf1 is selected from CH ₃ , a partially fluorinated or perfiuorinated alky! group having from 1 io 10 carbon atoms. 24. The melt-processabie tetrafluoroethene-based fluoropolymer according to any one of embodiments 13 to 23 wherein the fluorinated liquid is selected from the fluorinated (poly)ether according to formula {!!) wherein either Rf or Rf 1 or both are partially fluorinated,

25. An extrusion product comprising the fluoropolymer according to any on of embodiments 1 to 24.

26, The extrusion product of embodiment 25 comprising at least 50% by weight based on the total weight of the extrusion product of the fluoropolymer. 27. The extrusion product of embodiment 26 wherein the extrusion product is a melt pei!et or an extruded sheet. 28. A muiii-iayer article comprising the extruded sheet according to embodiment 27,

29. The multi-layer article of embodiment 28 wherein the. article is a protective sheet of a solar module, 30. The multi-layer article according to an one of embodiments 28 or 20 comprising one or more layers comprising a polymer selected from a polycarbonate, a silicone, a polyester or a polyamide.

31. A process of making an extruded article comprising providing a fluoropo!ymer composition comprising the fluoropolymer according to any one of embodiments 1 to 24, and subjecting the fluoropolymer composition to melt-extrusion to obtain an extruded article.

32. The process of embodiment 31 wherein the extruded article is a sheet having a thickness of from about 30 to 3,000 pm,

33. The process of embodiments 31 or 32 wherein the article is a multi-iayer article.

34. Method of making a fluoropolymer sheet comprising providing a fluoropolymer composition comprising the fluoropolymer according to any one of embodiments 1 to 24 and melt-extruding the fluoropolymer composition into a sheet,

35. Method of making a tetrafluoroethene-based fluoropolymer according to any one of embodiments 1 to 6 comprising polymerizing the monomers making up the fluoropolymer in an aqueous .emulsion polymerization using the fluorinated emuSsifier according to formula (I) as defined in any one of embodiments 7 to 10 and in the presence of the fluorinated liquid of formula (II) as defined in any one of embodiments 23 or 24.