Partially fluorinated mechanical

Whereas previously it had been customary to describe the process as producing exhaustive (i.e., complete) fluorination [78] (which indeed it does ) recent studies have demonstrated that it is possible to control the degree of fluorination [79], and, moreover, analysis of partially fluorinated products has cast new light on possible mechanisms in the process [70]. 

Similarly,both Meinert and Gambaretto, with their respective co-workers [80, 172, 175], have invoked this mechanism to explain the formation of partially fluorinated products in ECF reactions of the amines, tripropylamine, AT-methyl-morpholine, and a series of a,co-dimorpholino- and dipiperidino-alkanes. The selective order in which the hydrogens were substituted in these molecules was said to be consistent with that expected for the mechanism in that carbon atoms nearest to oxygen (in the morpholine rings), where the electron density is greatest, were the first to react, and those nearest to the quaternised nitrogen the last, not in a random order as might be expected in a radical mechanism. 

In a very recent publication [70] Rudiger has summed up these preceding results to propose a persuasive mechanism in which fluorination proceeds stepwise via partially fluorinated intermediates which are repeatedly adsorbed on the anode, fluorinated, and desorbed. 

Thus, it is stated, in this model of the ECF process, the physico-chemical properties of the partially fluorinated intermediates - or more precisely, the course of these properties with progressive fluorination - provide the clue to a better understanding of the mechanisms involved. 

Table 14.4. Mechanical Properties of Perfluorinated (10FEDA/4FMPD), Partially Fluorinated (6FDA/TFDB), and Unfluorinated (PMDA/ODA) Polyimide Films ...

These characteristics show that perfluorinated polyimides are promising materials for waveguides in integrated optics and optical interconnect technology. The thermal, mechanical, and optical properties of perfluorinated polyimides can be controlled by copolymerization in the same manner as partially fluorinated polyimides. ... 

One postulated reaction mechanism for electrochemical fluorination involves an intermediate nickel fluoride, with nickel in the oxidation stage +III/ + IV, as the active fluorination agent. The induction period in which the nickel fluoride layer is formed at the nickel surface can thus be explained. A radical fluorination mechanism has also been postulated, with oxidation of the fluoride anion to the radical, or as discussed below in the ECEC mechanism.15 The mechanism of this process is still a matter for debate. Reference should be made to a report that does not support the postulates of this section.21 For partial electrochemical fluorination, the ECEC mechanism is postulated as follows. In the first step the starting material is oxidized at the anode (E = electrochemical step). 

This review covers material mainly published since the earlier edition of this volume (see Houben-Weyl, Vol. 5/3, pp 53-72). The area has been reviewed,1-4 and lengthy discussions of the mechanisms of the fluorinations have been presented.5-9 With few exceptions these reagents lead to very high degrees of fluorination, although much of the emphasis in published work recently has been on partial fluorination. 

No other saturated acyclic hydrocarbons have been partially fluorinated over cobalt(III) fluoride, etc. It is clear from the results quoted above that partial fluorination is virtually valueless for the preparation of pure partially fluorinated acyclic hydrocarbons unless the need for a specific compound is particularly acute. The work cited is more notable for the light it sheds on the mechanisms of fluorination by cobalt(III) fluoride, etc., and the references should be consulted for extensive discussions on this matter. 

In this section, each method of generating carbon-based fluorinated radicals will be introduced and discussed in terms of mechanism, and it will be seen that virtually all of the useful methods for generating perfluoro and partially fluorinated radicals in a practical manner involve well defined and controlled free radical chain reactions. Some representative examples which demonstrate the preparative use of these methodologies will be presented in the final section of this review. 

This plastic is a partially fluorinated straight-chain polymer with a very high molecular weight. It is produced by free-radical polymerization mechanism in a solvent or a hybrid (a solvent/aqueous mixture) media, using an organic peroxide initiator. Copolymerization of tetrafluoroethylene and ethylene (CH2=CH2, molecular weight 28, CAS number 74-85-1) proceeds by an addition mechanism. 

Evidence against an ionic mechanism in such reactions is the observation that at 120°C, where reaction is slow, no acceleration was noted with added triethylamine. Evidence for a free radical mechanism is found in response to the presence of an olefin as a third reactant. Hydrocarbon olefins with one substituent intercept intermediate 1 more eflBciently than does tetrafluoroethylene, and they give partially fluorinated thiolanes of type 4. Regardless of the electronegativity of the olefinic substituent, yields are good (40-60% ), and products have the substituent on a carbon adjacent to sulfur in the ring (4). An intermediate of the type 5, in which nearly any substituent provides some stabilization to the adjacent radical center, is implicated. Cationic or anionic intermediates result in pronounced deviations from the results observed. 

Anodic fluorination has also been accomplished in aprotic solvents (acetonitrile, sulfolane, nitromethane) in the presence of fluorides in the form of HF, R3N HF, R4NF XHF and R4NBF4. Aromatic hydrocarbons (but not aliphatic ones as yet) have been oxidized by an ECE mechanism to partially fluorinated products. 

Partially fluorinated materials include ECTFE (ethylene trifluoroethylene), ETEE (ethylene tetrafluoroethylene), and PVDE (polyvinylidene fluoride). The partially fluorinated materials have higher mechanical properties but lower temperature ratings (<300°E/149°C), and chemical resistance. 

Partially fluorinated materials are ECTFE, ETFE, and PVDF. These materials have higher mechanical properties but lower temperature (<300°F/150°C) and chemical resistance. Fluoropolymer linings can cost 5-20 times more than thermoset linings so they are typically restricted to elevated temperature environment. 

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