Fluorinated polyurethanes

During the last two decades, many special fluoropolymers have been developed, such as fluorosilicones fluorinated polyurethanes fluorinated thermoplastic elas-... 

Polymer Chloro sulphonyl Acrylate Polyurethane Fluorinated... 

Over the years many fluoroelastomers have been prepared in addition to the materials described earlier in this chapter. These include fluorinated polyurethanes, fluorinated polyepoxides, hexafluoro-acetone/propylene oxide copolymers and polyfluorals. Many of these materials are thermally unstable, a fact which stresses the point that the presence of C—F bonds with their high bond strength is no guarantee of polymer thermal stability. One particular type of fluoroelastomer which is of technical importance, the fluorosilicone rubber family, are however of good thermal stability and are considered together with the silicone rubbers in a later chapter. 

The serendipitous discovery of polytetrafluoroethylene (PTFE) in 1938 by Roy J. Plunkett [82] and his co-workers at DuPont research laboratories has spurred the development of a variety of fluorine containing polymers, which include fluorosilicones, fluorinated polyurethanes, fluorinated thermoplastic elastomers, etc.. Many of the commercial fluoropolymers are suitable for melt processing via conventional injection molding, screw extrusion and blown film extrusion techniques. 

Synthesis and Properties. Several polymers containing HFIP-O groups have been investigated, the most common beeing epoxies and polyurethanes. The development of fluorinated epoxy resins and the basic understanding of their chemistry has been reviewed (127). 

Surfactants used as lubricants are added to polymer resins to improve the flow characteristics of the plastic during processing they also stabilise the cells of polyurethane foams during the foaming process. Surfactants are either nonionic (e.g. fatty amides and alcohols), cationic, anionic (dominating class e.g. alkylbenzene sulfonates), zwitterionic, hetero-element or polymeric (e.g. EO-PO block copolymers). Fluorinated anionic surfactants or super surfactants enable a variety of surfaces normally regarded as difficult to wet. These include PE and PP any product required to wet the surface of these polymers will benefit from inclusion of fluorosurfactants. Surfactants are frequently multicomponent formulations, based on petro- or oleochemicals. 

Various polymeric materials were tested statically with both gaseous and liquefied mixtures of fluorine and oxygen containing from 50 to 100% of the former. The materials which burned or reacted violently were phenol-formaldehyde resins (Bakelite) polyacrylonitrile-butadiene (Buna N) polyamides (Nylon) polychloroprene (Neoprene) polyethylene polytriflu-oropropylmethylsiloxane (LS63) polyvinyl chloride-vinyl acetate (Tygan) polyvinylidene fluoride-hexafluoropropylene (Viton) polyurethane foam. Under dynamic conditions of flow and pressure, the more resistant materials which binned were chlorinated polyethylenes, polymethyl methacrylate (Perspex) polytetraflu-oroethylene (Teflon). 

Synthetic Rubbers. Synthetic rubbers are polymers with rubberlike characteristics that are prepared from dienes or olefins. Rubbers with special properties can also be prepared from other polymers, such as polyacrylates, fluorinated hydrocarbons, and polyurethanes. 

These structures are well defined by conducting the polymerization in the presence of appropriate mono- and difunctional reagents. They are of considerable interest for the preparation of segmented block copolymers.24,25 For instance, the fluorinated macrodiols 21 have already been used to prepare an interesting new series of partially fluorinated segmented polyurethanes,26 and we are investigating other novel polymers that can be prepared from these intermediates. 

Because the forces of attraction prevail when molecules are brought into sufficiently dose proximity under normal conditions, release is best effected if both the strength of the interaction and the degree of contact are minimized. Aliphatic hydrocarbons and fluorocarbons achieve the former effect, finely divided solids the latter. Materials such as microcrystalline wax [64742 42-3] and hydrophobic silica [7631-86-9] combine both effects. Some authors refer to this combined effect as the ball bearing mechanism. A perfluoroalkylated fullerene nanosphere would perhaps be the ultimate example of this combined effect (17). These very general mechanistic remarks can be supplemented by publications on the mechanism of specific classes of release agents such as metallic stearates (18), fatty acids and fluorinated compounds (19), and silicone-coated rdease papers (20,21). The mechanism of release of certain problem adherents, eg, polyurethanes, has also been addressed (22,23). 

Much attention has been paid to the synthesis of fluorine-containing condensation polymers because of their unique properties (43) and different classes of polymers including polyethers, polyesters, polycarbonates, polyamides, polyurethanes, polyimides, polybenzimidazoles, and epoxy prepolymers containing pendent or backbone-incorporated bis-trifluoromethyl groups have been developed. These polymers exhibit promise as film formers, gas separation membranes, seals, soluble polymers, coatings, adhesives, and in other high temperature applications (103,104). Such polymers show increased solubility, glass-transition temperature, flame resistance, thermal stability, oxidation and environmental stability, decreased color, crystallinity, dielectric constant, and water absorption. 

Presently DOE is funding Air Products Chemical Company for the development of a fluorine surface treatment of tire rubber (crumb rubber) to modify its adhesion properties. This modified rubber could be used in making polymers such as polyurethane and epoxies. The tire rubber might also be used in certain plastics such as polystyrene and PVC, and in rubber products (68). 

The following fluoropolymers are commercially available in aqueous systems PTFE, PFA, MFA, FEP, ETFE, PVDF, THV Fluoroplastic, fluorocarbon elastomers, fluoroacrylates, and fluorinated polyurethanes. 

Introducing fluorine into polyurethane resins results in changes in properties similar to those seen with other polymers. Chemical, thermal, hydrolytic, and oxidative stability is improved. On the other hand, the polymer becomes more permeable to oxygen. Surfaces become more biocompatible and the capability to bond to other substances in contact with them is diminished.33... 

Raw materials used for the production of fluorinated polyurethanes are as follows ... 

The most frequently used method to prepare fluorourethanes commercially is the well-known addition reaction of polyisocyanates with polyols. Fluorine is most frequently introduced through the polyol component, since fluorinated polyisocyanates are relatively difficult to obtain and considerably more expensive than the nonfluorinated kind.34 Examples of fluorinated alcohols for polyurethane resins are listed in Table 8.3.35... 

Another manufacturing method involves irradiation by UV light, in which acrylic-modified polyurethane resins are used. Reactive fluorinated oligomers are reviewed in Reference 36. 

Fluorinated polyurethanes may also be prepared by treating the surface of an unfluorinated material with cold plasma of elemental fluorine37 or carbon tetrafluoride.38... 

Because of the low surface energy, resistance to chemicals and corrosive agents, and resistance to weathering, fluorinated polyurethanes are very well suited for protective coatings. They can be deposited in a desired location and thickness with the added advantage of curing mostly at ambient temperatures. 

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