Cross-link aryl ether

Another approach is shown in Figure 14. Here, we have an aryl ether cross-link resulting from a p-fluoroaromatic pendant group which undergoes facile nucleophilic substitution with the dlpotasslum salt of hexafluoroacetone blsphenol. Of course, n is much greater than m and can be controlled by altering stoichiometry. 

An intramolecular palladium(o)-catalyzed cross-coupling of an aryl iodide with a trans vinylstannane is the penultimate maneuver in the Stille-Hegedus total synthesis of (S)-zearalenone (142) (see Scheme 38).59 In the event, exposure of compound 140 to Pd(PPh3)4 catalyst on a 20% cross-linked polystyrene support in refluxing toluene brings about the desired macrocyclization, affording the 14-membered macrolide 141 in 54% yield. Acid-induced hydrolysis of the two methoxyethoxymethyl (MEM) ethers completes the total synthesis of 142. 

Polyesters [2] find use in fibers [poly(ethylene terephthalate), poly(ethylene oxybenzoate), poly(ester ethers), poly(ester amides), etc.] [1], coatings (especially unsaturated polyesters) [4], plasticizers, adhesives, polyurethane base resins, films, etc. Cross-linked polyesters prepared from glycerol and phthalic anhydride (alkyd resins) have been reviewed [20], High-melting poly aryl esters have been investigated for high-temperature applications. 

Figure 9.44 Lignin compounds, composed of connecting units of monolignols cross linked by carbon to carbon and the dominant /3-0-4 aryl to aryl ether bonds.

Since this study, the addition of repeat units capable of a postsynthetic transformation have been investigated. Bo et al. investigated the incorporation of an aryl bromide functionality on the Frechet-type repeat unit, which could be modified by a Suzuki cross-coupling with an aryl boronic acid.521 Freeman et al. explored the attachment of an allyl ether functionality on the same repeat unit,522 while Schultz et al. incorporated an aromatic spacer with two allyl groups to enable internal cross-linking via olefin metathesis.523... 

DiPietro RA, Duerig UT, Frommer JE, Gots-mann BW, Hedrick JL, Knoll AW, et al. Thermally reversible cross-linked poly (aryl ether ketone) media and method for high density data storage. US Patent 8012541, assigned to International Business Machines Corporation, Armonk, NY 2011. 

Matsumoto and Mochida [33], using NMR with a hydrogenated coal tar pitch mesophase carbon fiber, showed that the initial attack by oxygen was on -CH3 and -CH2- groups, with the gradual formation of carboxyls, esters and aryl carbonyls. Fairly stable cross-links were formed via phenols, ethers and esters. The workers also found that slower heating rates (0.5°C/min instead of 2.0°C/min) produced better mechanical properties and that the final choice would be controlled by the desired target properties and economics. 

Scheme 2.31 Structure of sulfonated fluorinated poly(aryl ether ketone) with cross-linking alkyne moiety. Taken from Ref. [145],...

Wang S, Zhao C, Ma W et al (2013) Macromolecular cross-linked polybenzimidazole based on bromomethylated poly (aryl ether ketone) with enhanced stability for high temperature fuel cell applications. J Power Sources 243 102-109... 

Several new classes of novel poly(a l ether)s have been synthesized which have very high glass transition temperatures. Most of these polymers are soluble in solvents such as dichloromethane, chloroform or chlorobenzene at room temperature and they can be cast into flexible films. Poly(aryl ether)s containing phthalocyanine moietes have also beem synthesized. Methods have been developed to introduce reactive functionality, e.g diaryl acetylene and diaryl cyclopropane moieties, into the backbone of these polymers so that they can be thermally cross-linked after fabrication. 

Recently, AEMs derived from poly(aryl ether oxadiazole) ionomers have also drawn attentions from researchers (Figure 11.22). Whether cross-linked or not, the... 

FIGURE 11.24 Chemical structure of self-cross-linked poly(aryl ether sulfone) ionomers. 

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