Appl. Sci. 2012, 2, 496-512; doi:10.3390/app2020496
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`OPEN ACCESS
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`
`
`applied sciences
`
`ISSN 2076-3417
`www.mdpi.com/journal/applsci
`
`Review
`Overview of the Development of the Fluoropolymer Industry
`
`Hongxiang Teng
`
`Polymer Research Institute, Department of Chemical and Biological Sciences, Polytechnic Institute of
`New York University, 6 Metrotech Center, Brooklyn, NY 11201, USA; E-Mail: hoteng@poly.edu
`
`Received: 23 April 2012; in revised form: 3 May 2012 / Accepted: 14 May 2012 /
`Published: 29 May 2012
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`Abstract: The present review briefly describes the development of the fluoropolymer
`industry in the past 70 years. Discussed are industrial fluoropolymers including
`polytetrafluoroethylene,
`polychlorotrifluoroethylene,
`polyvinylidenefluoride,
`polyvinylfluoride, ETFE, ECTFE, FEP, PFA, THV, Teflon AF and Cytop. Nafion is
`included as a special functional fluoropolymer material. These industrial fluoropolymers
`are introduced in the order of their discovery or time of first production, included are their
`chemical structures, thermal properties, mechanical properties, electrical and electronic
`properties, optical properties, chemical resistance, oxidative stabilities, weather stabilities,
`processabilities and their general applications. The main manufacturing companies for the
`different types of fluoropolymer products are also mentioned.
`
`Keywords: fluorine chemistry; fluoropolymer; fluorine industry
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`List of Abbreviations
`
`CTFE
`Cytop
`ECTFE
`ETFE
`FEP
`HFP
`Nafion
`PBVE
`PCTFE
`PDD
`PE
`PFA
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`chlorotrifluoroethylene
`homopolymer of PBVE
`copolymer of ethylene and CTFE
`copolymer of ethylene and TFE
`copolymer of fluorinated ethylene and propylene
`hexafluoropropylene
`TFE and perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acid copolymer
`perfluoro-3-butenyl-vinyl ether
`polychlorotrifluoroethylene
`perfluoro-2,2-dimethyl-1,3-dioxole
`polyethylene
`copolymer of TFE and PPVE
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`Novartis Exhibit 2255.001
`Regeneron v. Novartis, IPR2021-00816
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`perfluoropropylvinylether
`polytetrafluoroethylene
`polyvinylidenefluoride
`polyvinylfluoride
`copolymer of TFE and PDD
`tetrafluoroethylene
`poly(TFE-co-HFP-co-VDF)
`vinylidene fluoride
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`Appl. Sci. 2012, 2
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`PPVE
`PTFE
`PVDF
`PVF
`Teflon AF
`TFE
`THV
`VDF
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`1. Introduction
`
`Fluoropolymers are the polymer materials containing fluorine atoms in their chemical structures.
`From general organic polymer concepts, there are two types of fluoropolymer materials, i.e.
`perfluoropolymers and partially fluorinated polymers. In the former case, all the hydrogen atoms in the
`analogous hydrocarbon polymer structures were replaced by fluorine atoms. In the latter case, there are
`both hydrogen and fluorine atoms in the polymer structures. The fluoropolymer industry discussed
`here is mainly concerned with the perfluoropolymers, although in some cases the partially fluorinated
`polymers are included. In the latter case, there are both hydrogen and fluorine atoms in the polymer
`structures, along with additional elements in selected cases, such as polyvinylidenefluoride (PVDF)
`and polychlorotrifluoroethylene (PCTFE).
`Fluoropolymers possess excellent properties such as outstanding chemical resistance, weather
`stability, low surface energy, low coefficient of friction, and low dielectric constant. These properties
`come from the special electronic structure of the fluorine atom, the stable carbon-fluorine covalent
`bonding, and the unique intramolecular and intermolecular interactions between the fluorinated
`polymer segments and the main chains.
`Due to their special chemical and physical properties, the fluoropolymers are widely applied in the
`chemical, electrical/electronic, construction, architectural, and automotive industries. The world
`consumption of fluoropolymers is growing tremendously. Worldwide sales of fluoropolymers in 2000
`exceeded $2.0 billion compared with $1.5 billion in 1994. Even though the fluoropolymer industry
`was affected in the same way as other industries because of the economic downturn after 2008, there
`will be a turnaround along with the recovery of the world economy for fluoropolymer markets,
`especially
`in
`the motor vehicles, wire and cable, advanced batteries,
`fuel cells and
`photovoltaic modules.
`This review discusses the development of the most popular industrial fluoropolymers along with
`their chemical structures, basic properties, and general applications. For additional details, previously
`published books and journals would be helpful for monomer activities, polymerization methods,
`processing methods, polymer properties, and the applications [1–8].
`
`2. The Development of the Fluoropolymer Industry from 1930s ~ 1990s
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`1930s
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`the
`the discovery of
`industry began with
`fluoropolymer
`the
`The development of
`polytetrafluoroethylene (PTFE) by Dr. Plunkett at DuPont in 1938 [9]. The white powder found by
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`Novartis Exhibit 2255.002
`Regeneron v. Novartis, IPR2021-00816
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`Appl. Sci. 2012, 2
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`accident opened the magic door to one of the most important applied chemistry areas—the
`fluoropolymer industry—which greatly influenced the whole world in the following 70 years.
`PTFE is a linear polymer of tetrafluoroethylene (TFE) (Figure 1). The preparation of PTFE is
`hazardous because of the chemical properties of TFE. Therefore, special production equipments and
`processing conditions are required [10,11].
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`Figure 1. The polymerization of TFE.
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`F2C CF2
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`Initiator
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`*
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`+-+
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`*n
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`CF2 CF2
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`The chemical structure of PTFE is similar to that of polyethylene (PE), except that the hydrogen
`atoms are completely replaced by fluorine. Unlike the planer zigzag chain confirmation of PE, PTFE
`has a helical chain confirmation due to the larger fluorine volume. The rigid helical polymer chains
`can crystallize very easily and result in a high crystallinity (up to 98%). Because of the compact
`crystalline structure and the dense fluorine atoms, PTFE is the heaviest polymer material with a
`density of 2.1 g/cm3. The rigid polymer chain structure also caused a high melting temperature
`(~320 °C) and a high melt viscosity for PTFE, which made it difficult to process PTFE with the
`traditional methods for polymer materials. For quite a long time after the discovery of PTFE, scientists
`kept working on the different approaches to process PTFE materials, and it can be processed into all
`kinds of shapes for almost every application area.
`PTFE is available in granular, fine powder and water-based dispersion forms. The granular PTFE
`resin is produced by suspension polymerization in an aqueous medium with little or no dispersing
`agent. Granular PTFE resins are mainly used for molding (compression and isostatic) and ram
`extrusion. The fine PTFE powder is prepared by controlled emulsion polymerization, and the products
`are white, small sized particles. Fine PTFE powders can be processed into thin sections by paste
`extrusion or used as additives to increase wear resistance or frictional property of other materials.
`PTFE dispersions are prepared by the aqueous polymerization using more dispersing agent with
`agitation. Dispersions are used for coatings and film casting.
`One of the most distinguishing properties of PTFE is its outstanding chemical resistance, except for
`some extreme conditions such as molten alkali metals or elemental fluorine. Basically, PTFE is not
`soluble in any organic solvents. PTFE exhibits high thermal stability without obvious degradation
`below 440 °C. PTFE materials can be continuously used below 260 °C. The combustion of PTFE can
`only continue in a nearly pure oxygen atmosphere, and it is widely used as an additive in other
`polymer materials as a flame suppressant. PTFE has an extremely low dielectric constant (2.0) due to
`the highly symmetric structure of the macromolecules.
`The conventional PTFE has some limitations in its applications, such as poor weldability, low creep
`resistance, low radiation resistance, and high microvoid content. Therefore, research efforts were
`mainly trying to modify PTFE in different ways to overcome the shortcomings of the conventional
`PTFE. Modified PTFE significantly reduced melt viscosity by lowering the crystallinity through the
`incorporation of bulky comonomers into the polymer main chain. Modified PTFE has the advantages
`such as lower microvoid content and reduced permeation, better weldability and easier bonding
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`Novartis Exhibit 2255.003
`Regeneron v. Novartis, IPR2021-00816
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`Appl. Sci. 2012, 2
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`treatment, better sealing properties, excellent electrical insulation properties, smoother surface finishes
`and higher gloss.
`Even after modification, PTFE materials still have low tensile strength, wear resistance and creep
`resistance compared to other engineering polymers. The properties of the PTFE products are strongly
`dependent on the processing procedure, such as polymer particle size, sintering temperature and
`processing pressure. Therefore, other fluoropolymers are still needed for some specific applications
`where PTFE is not completely suitable.
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`1940s
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`In the beginning, PTFE polymers found no use for any application due to its insolubility, high
`melting temperature and extremely high melt viscosity. During World War II people realized the
`importance of this new material. At the time, the Manhattan Project was carrying out the development
`of the atomic bomb. Practically, U-235 needs to be separated from U-238 using differential diffusion
`of UF6. UF6 is highly corrosive to most metals and it was difficult to purify this material. As a result,
`the Manhattan project was looking for new corrosion resistant materials to meet the novel needs of
`purifying UF6. The then strange new material and its resistance to chemicals proved that PTFE could
`survive the extremely corrosive purification conditions. Therefore, PTFE got its first business order
`from the Manhattan project. After the war, PTFE was commercially available in 1947 with the
`trademark Teflon from DuPont to meet the growing market needs of the US and the world. The rate of
`market growth for PTFE has been 3%–5% per year for the past 30 years. In the late 1990s, annual
`consumption worldwide for PTFE was over 55,000 tons, which is almost doubled now. Some typical
`commercially available PTFE products are Teflon (DuPont), Polyflon (Daikin), Dyneon PTFE
`(Dyneon), and Fluon (Ashai Glass).
`Noticeably, even now PTFE still remains the largest type of fluoropolymers with about 70% of the
`total fluoropolymer market worldwide.
`
`1950s
`
`In 1953, a new fluoropolymer, polychlorotrifluoroethylene (PCTFE) was commercialized by M. W.
`Kellog Company under the trade mark Kel-F. PCTFE is produced by the free radical polymerization of
`chlorotrifluoroethylene (CTFE) with a linear polymer chain structure (Figure 2).
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`Figure 2. The polymerization of CTFE.
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`+:-:+
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`F
`C
`Cl
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`FF
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`C
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`*
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`*n
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`Initiator
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`F C
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`l
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`F F
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`>=<
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`High molecular weight PCTFE can be prepared by polymerization in bulk, in solution, in
`suspension and in emulsion forms [12]. Compared to PTFE, only one fluorine atom was replaced by
`the chlorine in PCTFE. The introduction of chlorine atom in the polymer structure interrupted the
`crystallization ability of the polymer main chain, and resulted in lower crystallinity, lower melting
`temperature, better intermolecular interaction, and better mechanical properties of PCTFE compared to
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`Novartis Exhibit 2255.004
`Regeneron v. Novartis, IPR2021-00816
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`PTFE. PCTFE showed higher hardness, higher tensile strength, higher resistance to creep, and less
`water vapor and gas permeability. One important advantage of PCTFE is its melt processability.
`PCTFE is easily melt processed and the products are more transparent. PCTFE can be used
`continuously from −100 °C to 200 °C. Especially, its better cold-flow characteristics made it more
`competitive to PTFE materials. It showed similar flame retardancy and better radiation resistance
`compared to PTFE. The chemical resistance and electrical properties of PCTFE are not as good as
`those of PTFE, but still better than most polymer materials.
`The price of PCTFE is higher than that of PTFE due to the expensive monomer as well as the small
`market size. Therefore, its main application is limited to use as a moisture barrier film in packaging
`and special engineering devices, where PTFE cannot meet the high performance requirements. Some
`examples are the aeronautical and space applications for cryogenic seals and gaskets. Low molecular
`weight PCTFE are used as oils, waxes and greases, inert sealants, lubricants for oxygen-handling
`equipment or corrosive media, plasticizers for thermoplastics and gyroscopic floatation fluids.
`PCTFE was originally produced by M. W. Kellog and 3M under the trade name of Kel-F [13].
`After 3M discontinued the production of PCTFE (1995) [14], Daikin purchased the manufacture rights
`to PCTFE and produced it under the trade name Neoflon. PCTFE resin is also produced by Honeywell
`as Aclar and by Arkema as Voltalef.
`
`1960s
`
`Considering the shortcoming of PTFE, researchers looked for new ideas to solve the existing
`problems. The copolymerization of TFE with other monomers offered many opportunities. The first
`TFE copolymer was FEP (fluorinated ethylene propylene), which was prepared by the random
`copolymerization of TFE and hexafluoropropylene (HFP). FEP was commercially introduced to the
`market in 1960 by DuPont.
`The structure of FEP is similar to PTFE except that a trifluoromethyl group was introduced along
`the side of the polymer main chain (Figure 3). FEP is generally prepared by the copolymerization of
`TFE and HFP in an aqueous medium with a free radical initiator and a dispersing agent. The
`comonomer ratio and the polymerization conditions are carefully controlled to achieve the desired
`copolymer composition and molecular weight, which are closely related to the melt viscosity, the
`processability and the mechanical properties of the final products [15,16].
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`Figure 3. The preparation of FEP.
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`+ - ++:-:+
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`F
`C
`CF3
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`*n
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`FF
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`C
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`CF2 CF2 m
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`Initiator
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`*
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`F3
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`F C
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`>=<
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`F F
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`F2C CF2
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`+
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`Generally, FEP contains about 5 mol% of HFP. The introduction of HFP units in the polymer main
`chain disrupted the crystallization ability of FEP copolymer compared with the homopolymer of TFE.
`The crystallinity of FEP is about 70%, and its melting temperature is in the range of 260–280 °C
`depending on the HFP content. It can be used continuously up to 200 °C. The molecular weight of FEP
`is much lower than that of PTFE and resulted in a much lower melt viscosity and better processability.
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`Novartis Exhibit 2255.005
`Regeneron v. Novartis, IPR2021-00816
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`FEP can be processed by the conventional polymer processing techniques such as injection molding,
`extrusion and film casting. FEP has better impact strength, better wear resistance, and less
`permeability for organic solvents compared with PTFE. The disadvantage of FEP is the poorer
`resistance to thermal stress cracking. FEP exhibits similar chemical resistance, weather resistance,
`flame resistance, radiation resistance, and the electrical properties to PTFE. FEP is easier to surface
`modify to increase wettability and adhesive bonding.
`FEP dispersions are generally used for coatings followed by the fuse treatment above the melting
`temperature of the polymer. The major applications of FEP are wire insulation, thermocouple wire
`insulation, chemical resistance liners for pipes and fittings, lined tanks for chemical storage, anti-stick
`applications, and sheet and film products for solar panels and solar collectors.
`About 65% of overall worldwide consumption for FEP is for plenum cable insulation. The
`increasing use of local area network (LAN) cable led to a huge increase in the market of FEP. Some
`typical commercial FEP products are Teflon FEP from DuPont, Neoflon FEP from Daikin, and
`Dyneon FEP from Dyneon.
`In 1961, DuPont introduced another fluoropolymer, polyvinylfluoride (PVF) (Figure 4) with the
`trademark Tedlar. Although only one hydrogen atom was replaced by a fluorine atom compared to the
`polyethylene, PVF showed more interesting properties than most fluoropolymers.
`
`Figure 4. The polymerization of VF.
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`+:-:+
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`FH
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`C
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`HH
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`C
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`*n
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`Initiator
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`*
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`H F
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`>=<
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`H H
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`PVF is prepared by the polymerization of vinyl fluoride (VF) in an aqueous medium using a free
`radical initiator. A higher pressure is necessary due to the lower polymerization activity of VF
`compared to TFE.
`The presence of the fluorine atom in PVF put it in between PE and PTFE in terms of crystallization.
`With a crystallinity of 40%, PVF has a melting temperature around 200 °C, and can be continuously
`used in the temperature range from –70 °C to 110 °C. The lower crystallinity of PVF compared to
`PTFE resulted in higher impact strength and better tensile strength. The relatively poor thermal
`stability of PVF makes PVF difficult to process traditionally. PVF film is manufactured using a
`plasticized melt extrusion method with plasticizers and stabilizers.
`The main uses of PVF are in films and coatings applications, such as the premier surface finish for
`aluminum and steel home siding. The excellent resistances to weather and radiation have led to the
`wide application of PVF as glazing materials for solar energy collectors.
`The formability of PVF is very important for lamination applications. It is critical that the laminate
`can stand bending during the roll forming process. PVF laminated steel finds application in industrial
`plants, warehouses, highway sound barriers and parking garages and provides long lasting aesthetics.
`Currently, DuPont is still the main company for PVF production. With a recent expansion it plans
`to achieve $1 billion in sales by 2012.
`Compared to VF, vinylidene fluoride (VDF) has one more fluorine atom on the same carbon in its
`chemical structure. The free radical polymerization of VDF resulted in a partially fluorinated,
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`Novartis Exhibit 2255.006
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`semi-crystalline polymer PVDF (polyvinylidenefluoride) (Figure 5), which was introduced by Pennsalt
`(now Arkema) with the tradename Kynar in 1961.
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`Figure 5. The polymerization of VDF.
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`+:-:+
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`FF
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`C
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`HH
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`C
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`*
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`*n
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`Initiator
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`F F
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`>=<
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`H H
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`PVDF is generally prepared by two kinds of polymerization methods, the suspension method
`and the emulsion method. Suspension polymerization produces PVDF with high head-to-tail structure
`in the polymer chains, which results in higher crystallinity, higher melting temperature, and better
`mechanical properties at elevated temperatures [17,18].
`PVDF is a polymer with several crystalline forms depending on the processing conditions. It has a
`melting temperature (~170 oC) significantly lower than that of the other fluoropolymers. The normal
`processing temperatures for PVDF are in the range 200–260 °C, and the continuous service
`temperature for PVDF is up to 150 °C. The crystallinity of PVDF increases significantly in the first
`week after processing and stabilizes after 4 weeks. This phenomenon increases crystallinity up to 65%
`and results in the intrinsic stress and the potential stress cracking.
`PVDF has very good chemical resistance to a wide range of chemicals, but it is not as good as that
`of other fluoropolymers. For example, PVDF can be swollen by polar solvents such as ethyl acetate
`and acetone. It shows medium flame resistance properties. PVDF also shares many of the
`characteristics of other fluoropolymers, such as thermal and oxidative stability, as well as outstanding
`weatherability. PVDF has substantially greater strength, wear resistance, and creep resistance than
`PTFE and FEP. PVDF undergoes cross-linking when exposed to ionizing radiation, which leads to a
`modification of its mechanical properties.
`PVDF has been used in the architectural coating industry, the wire and cable industry and the
`chemical industry for valves, pumps and bearings. Heat-shrinkable tubing made from PVDF is used in
`the electronics, aerospace, and aircraft industries. The alternative arrangement of fluorine and
`hydrogen atoms on the polymer main chain leads to an unusual polarity with a dramatic effect on
`dielectric properties. PVDF has a high dielectric constant (8 ~ 9) relative to the other fluoropolymers,
`and it also shows strong piezoelectricity. The promising developments include actuator materials,
`piezoelectric ceramics, piezoelectric composites and piezomicrosensors.
`The commercial PVDF products include Kynar from Arkema, Solef from Solvay, and Neoflon
`PVDF from Daikin. Solvay increased PVDF production capacity by 50% in 2011 to serve the strong
`growing demand.
`In the late 1960s, Nafion was discovered by Walther Grot of DuPont. Nafion is a fluoropolymer
`containing sulfonate groups onto a tetrafluoroethylene backbone (Figure 6) [19–27]. It is the first of a
`class of synthetic polymers with ionic properties which are called ionomers.
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`Novartis Exhibit 2255.007
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`Figure 6. The preparation of Nafion.
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`Appl. Sci. 2012, 2
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`
`CF2 CF2
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`+
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`*
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`CF3
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`CF2 CF
`\
`O
`I
`CF2
`\
`CF
`I
`O
`\
`
`CF2
`I
`CF2
`SO2F
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`\
`
`m
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`+
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`CF2 CF2
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`++ -\+
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`*
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`n
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`CF3
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`CF2 CF
`O
`I
`CF2
`\
`CF
`I
`O
`\
`
`CF2
`I
`CF2
`SO3H
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`\
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`Nafion
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`
`
`Nafion is synthesized firstly by the copolymerization of TFE and a perfluoro(alkyl vinyl ether) with
`sulfonyl acid fluoride. The resulting polymer is extruded into films and treated with hot aqueous
`NaOH converting the sulfonyl fluoride groups (-SO2F) into sulfonate groups (-SO3Na). This form of
`Nafion, referred to as the neutral or salt form, is finally converted to the acid form containing the
`sulfonic acid (-SO3H) groups. Nafion can be cast into thin films by heating in aqueous alcohol at
`250 °C in an autoclave. By this process, Nafion can be used to generate composite films, coat
`electrodes, or repair damaged membranes.
`The combination of the stable Teflon backbone with the acidic sulfonic groups gives Nafion many
`special characteristics. It is highly conductive to cations, making it suitable for many membrane
`applications. The Teflon backbone interlaced with the ionic sulfonate groups gives Nafion a high
`operating temperature, e.g. up to 190 °C. The combination of fluorinated backbone, sulfonic acid
`groups, and the stabilizing effect of the polymer matrix make Nafion a very strong acid, with pKa of
`−6. Nafion’s superior properties allowed for broad application. Nafion has found use in fuel cells,
`electrochemical devices, chlor-alkali production, metal-ion recovery, water electrolysis, plating,
`surface treatment of metals, batteries, sensors, Donnan dialysis cells, drug release, gas drying or
`humidifaction, and superacid catalysis for the production of fine chemicals (Gelbard, 2005). Nafion is
`also often cited for theoretical potential (i.e., thus far untested) in a number of fields.
`Although fuel cells have been used since the 1960s as power supplies for satellites, recently they
`have received renewed attention for their potential to efficiently produce clean energy from hydrogen.
`Nafion was found effective as a membrane for proton exchange membrane (PEM) fuel cells by
`permitting hydrogen ion transport while preventing electron conduction. Solid Polymer Electrolytes,
`which are made by connecting or depositing electrodes (usually noble metal) to both sides of the
`membrane, conduct the electrons through an energy requiring process and rejoin the hydrogen ions to
`react with oxygen and produce water. Fuel cells are expected to find strong use in the
`transportation industry.
`Nafion is the first and still one of the most important functional fluoropolymer materials. The
`further development in the fuel cell industry and the automotive industry offered the prominent future
`for the interesting polymer systems.
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`Novartis Exhibit 2255.008
`Regeneron v. Novartis, IPR2021-00816
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`1970s
`
`After discovering that ethylene has good copolymerization properties with fluorinated monomers,
`many new fluoropolymers were developed to achieve more favorable application properties. The first
`fluoropolymer containing ethylene units was ECTFE, which was introduced to the market by the
`Italian company Ausimont in 1970. ECTFE is an alternating copolymer of ethylene and CTFE
`(Figure 7).
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`Figure 7. The preparation of ECTFE.
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`+ - ++:-:+
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`*n
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`F
`C
`Cl
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`FF
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`C
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`CH2 CH2 m
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`Initiator
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`*
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`F C
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`l
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`F F
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`>=<
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`CH2
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`CH2
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`+
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`ECTFE is prepared by the copolymerization of ethylene and CTFE at relatively low temperatures
`(<10 °C) in an aqueous medium using a peroxide catalyst and a halogenated solvent chain transfer
`agent to regulate the molecular weight [28].
`ECTFE polymer chains pack in an extended zigzag confirmation, which results in a crystallinity of
`50%–60%. ECTFE has a melting temperature in the range of 220–245 °C depending on the
`polymerization methods. ECTFE can be used over a broad temperature range from −100 °C to 150°.
`ECTFE can be processed by the standard processing methods for traditional thermoplastics in the
`range of 260–300 °C. It is readily converted into fibers, filaments, films, sheets, and wire and cable
`insulation. Noticeably, the molten ECTFE is corrosive and special corrosion-resistant steels are used
`for screw and barrel components.
`As the copolymer with ethylene, ECTFE has moderate chemical resistance, flame resistance, and
`dielectric constant (2.6). While, it still has excellent radiation resistance, weathering resistance, and
`barrier properties, as well as good tensile, flexural and wear-related properties. The strength, wear
`resistance and creep resistance of ECTFE are significantly greater than that of PTFE and FEP. ECTFE
`film is the most abrasion resistant and highest tensile strength fluoropolymer film available.
`The single largest use of ECTFE is the flame-resistant insulation for wire and cable applications,
`extensively used for aircraft, mass transit and automotive wiring. ECTFE also finds applications in
`chemical process equipments and components. ECTFE is used in aerospace applications, such as
`gaskets for liquid oxygen and other propellants, components for spacecraft and aircraft cabins,
`convoluted tubing, abrasion resistant braid and hose for expandable conduit for space suits.
`At the end of 1999, Ausimont introduced a new family of ECTFE resins under the trademark Vatar,
`specifically designed to meet the requirements for plenum cable applications. ETCFE is currently
`manufactured by Solvay under the trademark Halar after acquiring Ausimont in 2002.
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`Figure 8. The preparation of PFA.
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`+ - -++:-:+
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`+
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`Novartis Exhibit 2255.009
`Regeneron v. Novartis, IPR2021-00816
`
`

`

`Appl. Sci. 2012, 2
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`After the introduction of FEP, further research on TFE copolymers led to the development of PFA
`(Figure 8)—a copolymer of TFE and perfluoropropylvinylether (PPVE), which was introduced in
`1972 by DuPont.
`Generally, PFA is prepared by an aqueous dispersion process. The copolymerization must be
`controlled carefully to produce a uniform copolymer with the required molecular weight and
`polydispersity [29,30].
`Due to the PPVE units in the polymer main chain, PFA has lower crystallinity compared to PTFE.
`Correspondingly, PFA has a lower melting temperature (305–310 °C), lower melt viscosity and better
`processability. This improvement for PTFE dramatically enlarged its market by lowering the
`processing cost and enriched the available product categories by the flexibility of thermoplastic
`processing.
`PFA shows comparable mechanical properties as FEP below 200 °C, and performs comparable
`mechanical properties as PTFE above 200 °C. The thermal stability of PFA is almost the same as that
`of PTFE and better than that of FEP. PFA has the same chemical resistance, flame resistance and
`radiation resistance as PTFE. The electrical properties of PFA and PTFE are similar. Importantly, PFA
`thin films have better transparency compared to PTFE.
`PFA can be processed by conventional melt techniques such as extrusion, injection molding and
`rotational molding. PFA powder can be used directly for extrusion or injection molding, and a PFA
`dispersion can be prepared for spray or dip-coating applications. Like PTFE, PFA can be filled with
`glass or carbon fibers, graphite or bronze powder to improve wear and creep properties.
`The main applications of PFA are chemical resistance components for valves, pumps and pipes.
`PFA is also widely used in the semiconductor manufacturing industries for high purity and chemical
`resistant moldings.
`The commercial PFA products are Teflon PFA from DuPont, Aflon PFA from Asahi Glass, Dyneon
`PFA from Dyneon, Neoflon PFA from Daikin, and Hyflon PFA from Solvay.
`After ECTFE, the other fluoropolymer containing ethylene units—ETFE was commercialized in
`1973 by DuPont. ETFE is comprised of alternating ethylene and TFE units in the polymer main chain
`(Figure 9).
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`Figure 9. The preparation of ETFE.
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`+ - ++-:-:+
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`CH2 CH2 m
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`Initiator
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`Due to the risk of explosive decomposition reaction, the copolymerization of ethylene and TFE
`must be conducted in special vessels at low pressure. Suspension polymerization is generally carried
`out in an inert chlorofluorocarbon solvent using fluorinated peroxides as initiator and methanol as a
`chain transfer agent [31,32].
`The polymer chains in ETFE adopt an extended zigzag conformation and a close packing. The
`crystallinity of ETFE ranges from 40% to 60%, and it has a melting temperature of 225–300 °C
`depending on the comonomer ratio and the processing method.
`
`Novartis Exhibit 2255.0010
`Regeneron v. Novartis, IPR2021-00816
`
`

`

`Appl. Sci. 2012, 2
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`ETFE possesses superior processability and improved mechanical properties compared to other
`TFE copolymers. ETFE can be processed by all thermoplastic processing methods such as injection
`molding, compression molding, blow molding, rotational molding, extrusion, and wire coating. ETFE
`has high tensile strength, high flexibility, excellent impact strength, moderate stiffness, good abrasion
`resistance and high cutting resistance. ETFE modified by glass fiber reinforcement is tougher and
`stiffer and has higher tensile strength than PTFE, PFA or FEP. ETFE has a broad operating
`temperature range from as low as –100 °C to 150 °C.
`As a copolymer of ethylene and TFE, ETFE has medium chemical resistance and flame resistance.
`Its radiation resistance is high with the advantage of being cross-linked by high-energy radiation. The
`radiation cross-linked ETFE wire insulation can be continuously used at 200 °C.
`The main application for ETFE is wire and cable insulation, accounting for 60% of its market.
`ETFE has good resistance to petroleum and fuel permeation, which resulted in a significant growth of
`ETFE as fuel tubing.
`The commercial ETFE products include Tefzel from DuPont, Fluon from Asahi Glass, Halon ETFE
`from Solvay, Neoflon ETFE from Daikin, and Dyneon ETFE from Dyneon.
`
`1980s
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`Before 1980s, all the industrial fluoropolymers were semicrystalline materials. Crystalline
`fluoropolymers have certain shortcomings such as low optical clarity, high creep and poor solubility,
`which limited their processability and the type of applications. In 1985, DuPont developed an
`amorphous perfluoropolymer—Teflon AF. Teflon AF is a copolymer of TFE and perfluoro-2,2-
`dimethyl-1,3-dioxole (PDD) (Figure 10). The copolymerization of PDD and TFE is carried out in
`aqueous media with a fluorinated surfactant and ammonium persulfate as an initiator [33,34]. The
`composition of the copolymers could be adjusted by the comonomer feeding ratios. Different grades of
`Teflon AF products were prepared for different applications. At the same time, Asahi Glass also
`introduced a new amorphous perfluoropolymer—Cytop. Cytop is a homopolymer obtained via the
`cyclo-polymerization of perflu