Partially Fluorinated Polymers

Partially fluorinated polymers, notably polyfvinylidene fluoride) (PVDF) and its copolymers, are readily processed by conventional polymer technology and generally have chemi-... 

PFA and MFA exhibit considerably better electrical properties than most traditional plastics. In comparison with the partially fluorinated polymers, they are only slightly affected by temperature up to their maximum service temperature.54... 

Separator Polymer Polypropylene, Polyethylene partially fluorinated polymer)... 

The era of fluoropolymers began with the serendipitous discovery of PTFE by Roy Plunkett of DuPont Companywhile conducting research to find new refrigerants. A number of fluoroplastics have been developed since the discovery of PTFE. They are divided into two classes of perfluorinated and partially fluorinated polymers. Perfluorinated fluoropolymers... 

PVDF is a linear partially fluorinate polymer containing 59.4 wt% fluorine and 3wt% hydrogen. The high level of intrinsic crystallinity, typically near 60%, provides stiffness, toughness, and creep resistant properties. Incorporation of various fluorinated comonomers at low levels, typically about 5-20 wt%, enhances flexibility and clarity of PVDF by reducing the crystallinity, which in turn reduces the end use temperature rating. PVDF is commercially produced via free radical polymerization either with emulsion or suspension processes. 

Current photoresists cannot be used for 157 nm technology, mainly because their transmittance at 157 nm is too low. Although materials with aromatic substructures are quite useful for the 248-nm process, only purely aliphatic polymers are employed in the current 193 nm technology. For an illuminating wavelength of 157 nm, even the absorptivity of most aliphatic compounds is too high. Therefore, only partially fluorinated polymers with absorption characteristics carefully optimized by experiment [10] and molecular modeling [11] can be used. The solubility switch after illumination is usually achieved by addition of a photo-activatable super-acid (e.g. a diaryl iodonium hexafluoroantimonate) [12], which typically cleaves an add-labile tert-butyl ester in the polymer (Scheme 4.9). 

Partially fluorinated fluoropol5miers are significantly different from the perfluoropol5miers with respect to properties and processing characteristics. For example, perfluoropolymers are more thermally stable but physically less hard than partially fluorinated polymers. Both classes of fluoropolymers are discussed in Ch. 3. 

In a study of weathering resistance, three partially fluorinated polymers (ETFE, PVDF, and PVF) were exposed to ultraviolet light in a QUV Weather-... 

The chemical nature of the base polymer is an important aspect in membrane development. There has been preference for the thermally stable fluorinated polymers over hydrocarbon polymers. Fluorine-containing polymers, characterized by the presence of carbon-fluorine bonds, are widely used as the base matrices owing to their outstanding chemical and thermal stability, low surface energy, and the ease of modiflcation of various properties by the grafting method. Per fluorinated polymers and partially fluorinated polymers combining hydrocarbon and fluorocarbon structures are excellent candidates as base polymers. For instance, fluorinated FEP has drawn wide attention due to its reasonably good radiation stabiUty [58]. 

Figure 1. Refractive-index dependence of the polymers on wavelength. benzyl benzoate doped PMMA PMMA dibutyl phthalate doped partially fluorinated polymer A partially fluorinated polymer.

Radiation grafting has been investigated now for several years as an attempt to balance cost and stability in the development of proton-conductive membranes. Partially fluorinated polymers like perfluoroethylenepropylene (FEP) [159-161] or poly(vinylidene fluoride)(PVDF) [162, 163] are submitted to gamma [159, 160] or electron [162, 163] radiation and immersed in a mixture of styrene and divinyl benzene (for crosslinking) ... 

Traditionally, a fluoropolymer or fluoroplastic is defined as a polymer consisting of carbon (C) and fluorine (F). Sometimes these are referred to as per-fluoropolymers to distinguish them from partially fluorinated polymers, fluoroelastomers, and other polymers that contain fluorine in their chemical structure. For example, fluorosilicone and fluoroacrylate polymers are not referred to as fluoropolymers. The monomers used to make the various fluoropolymers are shown in Figure 9.1. 

The fully fluorinated polymers, that is, polytetrafluoroethylene (PTFE) and the copolymer of tetrafluoroethylene and hexafluoroethylene (FEP) are difficult to adhere to and, to obtain satisfactory adhesion, it is usually necessary to pre-treat these polymers. With partially fluorinated polymers, it is often possible to obtain good adhesion without a pre-treatment for example, good bond strengths have been obtained with poly(vinyl fluoride) and poly(vinylidene fluoride) and polychlorotrifluoroethylene and the copolymer of chlorotrifluoroethylene and vinyl fluoride. ... 

Aqueous and alcoholic solutions of group 1 hydroxides provide effective treatments for partially fluorinated polymers. Flame treatment is also effective with these polymers. ... 

A partially fluorinated polymer, also soluble in polar solvent, is PVDF. It is characterized by high performance, chemical resistance, good thermal stability, and resistance to UV light and oxidant attack (Chin et al., 2006). PVDF membranes have been used primarily in the construction of submerged modules, widely used in bioreactors because of their lower costs with respect to other types of photocatalytic membranes (Sopajaree et al., 1999 Chin, Lim, Chiang, Fane, 2007 Jia et al., 2006, Fu, Ji, Wang, Jin, An, 2006). 

Table 2. Radiochemical Yields of Cross-Linking and Scission for Several Partially Fluorinated Polymers...

The practical applications of fluoropolymer membranes especially in the areas of purification and separation related to potable water production, wastewater treatment and bioprocessing, have been limited to some extent by their hydrophobic and inert surface properties. Among the different modification techniques, graft copolymerization of hydrophilic monomers, or inimers for further surface reactions, from fiuoropolymers has been useful and effective in improving the physicochemical properties of the parent fluoropolymer with minimum alteration of their desirable bulk properties. Apart from fiilly fluorinated polymers, most of the partially fluorinated polymers can dissolve in polar organic solvents, such as Ai,Ai-dimethylformamide (DMF), A,A-dimethylacetamide (DMAc), NMP, and dimethyl sulfoxide (DMSO), but are insoluble in water, alcohols, and hydrocarbons. 

Partially Fluorinated Polymers Partially fluorinated polymers (e.g., THV, ETFE, PVDF, and the like) as well as perfluorinated polymers in combination with larger amounts of hydrocarbon-containing polymers (e.g., blends, laminates) can be recycled by HTC processes into monomers only with low/moderate yields [97] usually these EOL-polymers are landfilled or incinerated in small portions due to the corrosive HF. 

The melt processible fluoroplastics are often desired due to the cost benefits of melt extrusion over paste extrusion. FEP, PEA and specially formulated melt processible perfluoroplastics are used in many of these applications however, in some of these applications, perfluoroplastics may not be the ideal choice. In cases where high cut-through resistance and better tensile properties are required, it is often desirable to employ a partially fluorinated polymer such as ETFE (ethylene-tetrafluoroethylene). ETFE is the copolymer of ethylene and TEE [16] that normally includes an additional termonomer to increase the flexibility required in commercial applications [17]. The increased physical and electronic interactions of the ETFE polymer chain are responsible for the comparatively enhanced physical properties. Additionally, the partially fluorinated polymers may be cross-linked to further improve physical properties. These benefits, however, are obtained at the expense of the unique properties of perfluoroplastics discussed in the Introduction and Overview. 

Perfluorocyclobutane (PFCB) polyaryl ethers are one such class of partially fluorinated polymers which combine the processability and durability of engineering thermoplastics with the optical, electrical, thermal, and chemical resistant properties of traditional fluoroplastics. Developed originally at The Dow Chemical Company" in Freeport, TX, PFCB polymers are prepared by the radical mediated thermal cyclopolymerization of trifluorovinyl ethers (Figure 1) and have, to date, provided a variety of thermoplastic and thermosetting materials possessing a tunable range of... 

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