Oligomerization of tetrafluoroethylene

A process developed by ICI [95-97] is based on anionic polymerization of tetrafluoroethylene. Unlike high-molecular-weight poly(tetrafluoroethylene) produced by free-radical polymerization, anionic polymerization catalyzed by a fluoride (e.g., cesium, potassium, or tetraalkylammonium fluoride) produces highly branched oligomers. The main products are a tetramer, a pentamer, and hexamers (Fig. 2.7). 

The pentamer, the most abundant of the oligomers, is an unsaturated per-fluorocarbon susceptible to a nucleophilic attack. The pentamer can react with a phenol. The product can be sulfonated to form a sulfonic acid, which after neutralization, functions as an anionic surfactant  

Hexamers (only two most abundant isomers shown) 

Reaction of the pentamer with p-cresol yields an ether which can be oxidized to yield a fluorinated carboxylic acid. The acid can be neutralized to give an anionic fluorinated surfactant  

The same fluorinated carboxylic acid can be prepared by reacting the pen-tamer with p-hydroxymethylbenzoate and hydrolyzing the ester formed  

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Scheme 2.114 Cesium fluoride-catalyzed oligomerization of tetrafluoroethylene [38].

Fluorocarbons. Fluorocarbons are prepared primarily by the electrolytic substitution of fluorine for hydrogen on the carbon chain of carboxylic acid fluorides or sulfonyl fluorides. They may be completely fluorinated (per-fluoro-) or have a terminal hydrogen atom. In that respect, it is important to know which type of chain is present in a material, since the properties of the two may differ significantly in critical applications. They are also prepared by the oligomerization of tetrafluoroethylene. Linkage to many hydrophilic groups is accomplished through a short-chain hydrocarbon unit. 

Oligomers of tetrafluoroethylene (particularly pentamer) are prepared by oligomerization of tetrafluoroethylene in an organic solvent in the presence of a fluoride compound and a crown ether [280],... 

Direct fluorination with elemental fluorine is not practical for commercial synthesis of fluorinated surfactants. Elemental fluorine is extremely reactive and difficult to handle. The heat of formation of the C—bond (about 460 kJ/mol or 110 kcal/mol) and the H—F bond (566 kJ/mol or 135 kcal/mol) exceeds that of the C—C bond (about 348 kJ/mol or 83 kcal/mol) [1]. Hence, the fluorination with elemental fluorine leads to a violent fragmentation of the substrate unless the reaction is carefully controlled and the reaction heat effectively dissipated [2,3]. Commercially important pathways to fluorinated surfactants are electrochemical fluorination, telomerization, and oligomerization of tetrafluoroethylene [4-6]. 

Oligomerization of tetrafluoroethylene provides intermediates for amphoteric fluorinated surfactants. The tetrafluoroethylene pentamer reacts with phenol to form a phenyl ether [96]. Chlorosulfonation of the phenyl ether with chlorosul-fonic acid yields a sulfonyl chloride, which is allowed to react with A dimethyl-propanediamine ... 

Materials of this type have been sold by Du Pont Co. under the Freon E and Krytox trademarks. Perfluorinated materials stmcturaEy similar to those in equation 11 have been prepared by Ausimont by the low temperature irradiation of either hexafluoropropylene or tetrafluoroethylene with oxygen followed by heating and/or irradiation and have been sold as Fomblin Hquids (52). An isomeric polyether, Demnum, prepared by the oligomerization of 2,2,3,3-tetrafluorooxetane followed by fluorination has been commercialized by Daikin (eq. 12). 

Prepa.ra.tlon There are five methods for the preparation of long-chain perfluorinated carboxyUc acids and derivatives electrochemical fluorination, direct fluorination, telomerization of tetrafluoroethylene, oligomerization of hexafluoropropylene oxide, and photooxidation of tetrafluoroethylene and hexafluoropropylene. 

Catalytic properties of the active acid form of the composites obtained in comparison with random copolymers of tetrafluoroethylene and PFAVESF (Nafion-type) were investigated in esterification, oligomerization, and aromatic compounds alkylation reactions. 

A significant advantage of conducting polymerization and oligomerization of fluoroalkanes in carbon dioxide rather than other solvents is the absence of chain transfer to CO2. Radicals generated from fluoroalkene monomers such as tetrafluoroethylene (TFE) are quite electrophilic, and will undergo facile chain transfer to virtually any hydrocarbon that is present in the system. Moreover, highly reactive monomers such as TFE can be handled more safely as... 

The acid-base Nafion composite membranes include blends of Nafion with polypyrrole (PPy) [98-104], polybenzimidazole (PBI) [105-107], poly (propyleneoxide) (PPO) [108, 109], polyfurfuryl alcohol (PFA) [110], poly(vinyl alcohol) (PVA) [111-115], sulfonated phenol-formaldehyde (sPF) [116], polyvinylidene fluoride (PVdF) [117-122], poly(p-phenylene vinylene) (PPV) [123], poly(vinyl pyrrolidone) (PVP) [124] polyanifine (PANI) [125-128], polyethylene (PE) [129], poly(ethylene-terephtalate) [130], sulfated p-cyclodextrin (sCD) [131], sulfonated poly(ether ether ketone) (sPEEK) [132-135], sulfonated poly(aryl ether ketone) (sPAEK) [136], poly(arylene ether sulfone) (PAES) [137], poly(vinylimidazole) (PVl) [138], poly(vinyl pyridine) (PVPy) [139], poly (tetrafluoroethylene) (PTFE) [140-142], poly(fluorinated ethylene-propylene) [143], sulfonated polyhedral oligomeric silsesquioxane (sPOSS) [144], poly (3,4-ethylenedioxythiophene) (PEDT) [145, 146], polyrotaxanes (PR) [147], purple membrane [148], sulfonated polystyrene (PSSA) [149, 150], polystyrene-b-poly(ethylene-ran-butylene)-bpolystyrene (SEES) [151], poly(2-acrylamido-2-methyl-l-propanesulphonic acid-co-l,6-hexanediol propoxylate diacrylate-co-ethyl methacrylate) (AMPS) [152], and chitosan [31]. A binary PVA/chitosan [153] and a ternary Nafion composite with PVA, polyimide (PI) and 8-trimethoxy silylpropyl glycerin ether-1,3,6-pyrenetrisulfonic acid (TSPS) has also been reported [154]. 

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