Potassium 18-crown-6 poly ether

Potassium chloride crown poly ether Crown polyethers as phase transfer catalysts... 

Potassium ieri-butoxidel 18-crown-6 poly ether... 

Thus poly(p-xylene carbonate) has been synthesized from potassium carbonate and p-xylene dibromide under the influence of 18-crown-6-ether. The crown ether formed a complex with the metal cation, thereby providing highly reactive unsolvated anions. Aromatic polycarbonates have been prepared and subjected to studies of their heat stability, mechanical strength, transparency, and electrical properties. Spiro o-carbonates have been synthesized and their poly-racrizability, by cationic initiation, has been assessed. 

In 1992, Irie et al. synthesized the ion-sensitive poly(NIPAM-c< -BCAm) 5 polymer consisting of Af-isopropylacrylamide units and benzo[18]-crown-6-ether units (BCAm) for the first time (Figure 5.10). The polymer 5 showed a 31.5°C LCST in an aqueous solution. The LCST value increased with increasing concentration of potassium chloride. No similar increase in the LCST was observed for only PNIPAM. 

Metallation of weak hydrocarbon acids by potassium hydride-18-crown-6 poly ether in tetrahydrofuran and the relative acidity of molecular hydrogen. E. Buncel and B. Menon, J. C. S. Chem. Commun., 648 (1976)... 

Concerning the synthesis of graft copolymers, Jedlinski et al. have prepared poly(MMA-g-(3BL) copolymers via anionic grafting of 3BL from a modified PMMA backbone [85]. PMMA chains were partially saponified by potassium hydroxide and complexed by 18C6 crown ether so as to act as multifunctional mac-... 

Cyclic poly(ethylene oxides) ( Crown ethers ), Potassium hydroxide Le Goaller, R. et al., Synth. Comm., 1982, 12, 1163—1169... 

A large effective cation size should suppress the cation-siloxane coordination, favor the Iree ion pair 3 in reaction 10, and enhance charge separation. The anticipated effects would be values of n approaching 1 in the rate equation 9, greatly enhanced rates of polymerization, and suppressed formation of cyclosiloxanes. Evidence that these effects are achieved is indicated by the effects seen with R4N countercations (35), the lithium cryp-tates (25, 27), and the crown ether-potassium silanolate complexes (39, 40). Additional evidence for the influence of the countercation on the equilibria is seen in deviations of the amounts of oligomer produced in equilibrated poly(dimethylsiloxane) from the normal distribution caused by specific interactions between the potassium silanolate chain ends (37, 38). More de-... 

In contrast to conventional cation exchangers, a reversed elution order is observed with crown ether phases, which is mainly determined by the size ratio between crown ether ring and alkali metal ion. Due to the high affinity of poly(benzo-15-crown-5) toward potassium and rubidium ions, these are more strongly retained than lithium, sodium, and cesium ions, respectively. However, the complexing properties of crown ethers also depend on the counter ion being employed. Thus, in potassium salts, for example, an increase in retention in the order KC1 < KBr < KI is observed with an increasing size of the counter ion. 

Cyclic poly(ethylene oxides) ( Crown ethers ), Potassium hydroxide... 

C-allylation of PhO" Na with H2C=CHCH2C1 in a variety of solvents in the presence of different crown ethers is most effective in each case when using poly(vinylbenzo-15-crown-5)polyether. Only in the presence of the crown ethers 15-crown-5 and 18-crown-6 are the anions in potassium phthalimide and sodium saccharinate, respectively, sufficiently activated to bring about nucleophilic aromatic substitution of the 4-fluorine in pentafluoropyridine. The formation of 2,4-dinitrophenol, in addition to the expected ether, from 2,4-dinitrochlorobenzene and potassium 2-propoxide in 2-propanol-benzene (1 1), in the presence of dicyclohexyl-18-crown-6 polyether, has been accounted for on the basis of a nucleophile-radical reaction (5rn1)/ ... 

Acetoxylation of poly(vinyl chloride) can be carried out under homogeneous conditions. Crown ethers, like 18-crown-6, solubilize potassium acetate in mixtures of benzene, tetrahydrofuran, and methyl alcohol to generate unsolvated, strongly nucleophilic naked acetate anions. These react readily with the polymer under mild conditions. Substitutions of the chlorine atoms on the polymeric backbones by anionic species take place by a Sn2 mechanism. The reactions can also proceed by a Sivl mechanism. That, however, requires formations of cationic centers on the backbones in the rate-determining step and substitutions are in competition with elimination reactions. It is conceivable that anionic species may (depending upon basicity) also facilitate... 

There are fewer reports of linear, acyclic, ion-binding polymers. It has been reported that poly(oxyethylene) improves the solubility of alkali metals in ethers such as tetrahydrofuran, dime thoxy ethane, and diglyme, stabilizes fluorenyl alkali metal compounds, accelerates Williamson reactions and accelerates several other nucleophilic reactions.All of these effects were attributed to the ability of poly(oxyethylene) to complex with cations in solution. Yanagida and coworkers studied the alkali metal cation complexation of poly(oxyethylene), using a picrate salt extraction technique similar to the one used by Pedersen and Frensdorff. Polymers with more than 23 oxyethylene units were effective iono-phores for potassium, with degrees of extraction (percent extracted) comparable to crown ethers. The extractability per oxyethylene unit was nearly constant, and the complex stability increased linearly with increasing numbers of repeating oxyethylene units. Seven oxyethylenes were the minimum number of repeat units necessary to bind potassium ion effectively in the aqueous phase. The less efficient extraction of short-chain poly(oxyethylene) is apparently caused by its hydrophilic character. 

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