Fluorine-substituted polymers

Fluorine-substituted polymers have excellent heat- and chemical-resistance properties, and low surface energy and low dielectric constant, etc. Another... 

The presence of carbon—fluorine bonds in organic polymers is known to characteristically impart polymer stabiUty and solvent resistance. The poly(fluorosibcones) are siloxane polymers with fluorinated organic substituents bonded to siUcon. Poly(fluorosibcones) have unique appHcations resulting from the combination provided by fluorine substitution into a siloxane polymer stmcture (see Silicon compounds, silicones). 

This polymer is the completely fluorine-substituted analogue of poly(ethylene) i.e. [CF2CF2—The amount of this polymer produced commercially is very small compared with the output of many other synthetic polymers, but it has a number of important specialised uses and so is worth considering briefly. 

Comparative analysis of different fluorine-substituted PPVs 75-77 has been performed by Karasz and coworkers [130]. Polymers 75 and 76 exhibit slightly blue-shifted UV absorbance relative to PPV 1, but remarkably, have substantially red-shifted PL and EL emission bands. 

Fluorine-substituted thiocarbonyl compounds have been studied even more intensively than thioformaldehyde and thioacetone. These compounds have a very rich chemistry of which polymerization is only a part. The simplest member of this class is fluorothiocarbonyl fluoride, CF2==S, which also forms the most interesting polymers. Other members that have been investigated include a variety of fluorothioacyl halides and a number of fluorothioketones. Because... 

The UV-visible absorption maxima and edges of the various PPV derivatives are summarized in Table 1. PFPV [7] with electron-withdrawing substituent shows a blue-shifted absorption at 410 nm and perfluorinated biphenyl substituted PPFPV [20] shows more blue-shifted absorption at 400 nm. Benjamin et al. [21] have reported that a copolymer composed of the PPV part and the 2,3,5,6-tetrafluoro-PPV part showed a blue-shifted absorption compared with that of unsubstituted PPV. These shifts are explained as being a result of the inductive electron withdrawing properties of the fluorine substitution leading to reduced electron density in the conjugated polymers and leading to an increase in the HOMO-LUMO band gap. 

The XPS data reveal that a considerable degree of rearrangement of the injected fluorocarbon is involved in the plasma polymerization process. The relative quantities of CF, CF2, CF and non-fluorine substituted features are readily monitored by XPS and show a strong dependence on the injected fluorocarbon. As the fluorine content of the injected material decreases so does that of the polymer. Table 2 lists the measured F/C stoichio-... 

Diacetylene monomers with aromatic groups directly bonded to the triple bonds typically do not undergo extensive conversion to polymer (64). More extensive conversions appear to take place in fluorine-substituted diphenyl diacetylenes (65), and this may be an important new vector in PDA research. 

Figure 9.4. Polymers with very large dielectric constants caused by asymmetric fluorination. (a) Poly(vinylidene fluoride), where the fluorine substitution is symmetric at a given C atom, but asymmetric (alternating) along the chain, (b) Poly[oxy(methyl y-trifluoropropylsilylene)].

For their research on the effects of fluorine substitution on peptide conformations (see below), Zondlo and coworkers developed a divergent synthesis of peptides (Thr-Tyr-X-Asp) (TYXN) containing an internal substituted Tyr-X (X = Pro or substituted Pro) sequence. Polymer-supported peptides containing hydroxyproline were prepared, modified, and released by standard acidic cleavage and deprotection. This is summarized in Fig. 3.13. 

Price, S.G., Stuart, A.G., Yang, L., Zhou, H., You, W., 2011. Fluorine substituted conjugated polymer of medium band gap yields 7% efficiency in polymer-fuUerene solar cells. J. Am. Ghem. Soc. 133, 4625-4631. 

In this paper, we analyze the effect of fluorine substitution in the polymers listed above by dielectric analysis (DEA), dynamic mechanical analysis (DMA) and stress relaxation measurements. The effect of fluorination on the a relaxation was characterized by fitting dielectric data and stress data to the Williams, Landel and Ferry (WLF) equation. Secondary relaxations were characterized by Arrhenius analysis of DEA and DMA data. The "quasi-equilibrium" approach to dielectric strength analysis was used to interpret the effect of fluorination on "complete" dipole... 

Under the influence of anionic catalysts, silyl ethers react with perfluorinated olefins to produce exceptionally high yields of partially fluorinated vinyl ethers. The number of vinyl fluorines substituted can be controlled for a wide variety of fluorinated olefins and silyl ethers. Application of this reaction to difunctional starting materials affords quantitative yields of condensation polymers of moderate molecular weight. 

Since the conversion of fluorinated olefins to vinyl ethers is knownl, it should be emphasized that the principal benefit from the silyl ether chemistry is increased selectivity and yield. Base-catalyzed reaction of alcohols and fluoroolefins almost always gives a mixture of substitution and addition products, but clean substitution occurs with silyl ethers. Homogeneity, which persists during bulk polymerization, is an additional attractive feature. Substitution of the first fluorine in a 1, 2-disubstituted perfluorinated olefin proceeds more rapidly than subsequent fluorine substitution in the product vinyl ether. The 2/1 adducts shown in Scheme 4 are therefore conveniently prepared in excellent yield. On a laboratory scale, these difunctional vinyl ethers permit good control of stoichiometry required for polymer formation. 

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