Crown ethers complexes with polymers

Vignier, M., Abadie, M., Schu6, E, and Kaempf, B., Preparation and UV characterization of crown-ether complexes with alkaline metals, Eur. Polymer J., 13, 213,1977. Vignier, M., Collet, A., Schue, E, and Kaempf, B., Preparation and characterization of alkaline radical anions in THE, /. Phys. Chem., 82, 1578, 1978. 

With soft anions crown-ethers are more efficient than quaternary salts, the reverse being observed when less polarizable nucleophiles are used. This is explained by the different extent of complexation of crown-ethers which depends not only on the complexed cation, but also on the anionic counterpart. Swelling and hydration measurements of polymer-supported crown-ethers in toluene/aqueous KY showed that the content of water in the imbibed solvent increases with the loading. This leads to a progressive polarity increase within the polymers and to a better crown-ether complexing... 

Gagn6 et al. developed polymer active sites that additionally contained a receptor (recognition sites) displayed in the outer sphere of the metal center (reactive site). The Suzuki reaction of /)-bromoanisole with phenyl boronic acid and the allylation of dimethyl malonate with allyl acetate were both chosen to assess the presence and/or effect of the crown-ether in crown-ether-molecular imprinting polymer-palladium complex. The results showed that molecular imprinting can be used to functionalize the second-coordination sphere of a transition metal complex and subsequently affect its catalytic behavior. 

Some vinyl fluoride-based polymers with side chains of perfluorosulfonic acid (the Nation family) are important ion-exchange membrane materials used in practice for electrolysis of NaCl and in certain fuel cells. They show a proton conductivity of 0.01 S cm- at room temperature. However, such fast ionic transport occurs only when they are swollen with water. It is therefore not appropriate to call them solid electrolytes in the tme sense of the word. It was in 1970 that anionic conductivity, though not high, was reported for crown ether complexes such as dibenzo-18-crown-6 KSCN, in which cations are trapped by the ligand. " A few years later much higher cationic (instead of anionic) conduction was found in complexes of a chain-like polyether such as PEO or PPO with alkaline salts here, PEO stands for poly(ethyleneoxide), (CHjCHj-O), and PPO for poly(propyleneoxide)."2>"3 These were the flrst examples of tme polymer solid electrolytes and were followed by a great number of studies. Polymeric electrolytes are advantageous in practice because they are easily processed and formed into flexible Aims. 

The selectivity is nevertheless greatly affected when a swelling solvent of the gel is added. The solvents used are good solvents of the crown ethers but with no specific interaction with the polymer backbone. The formation of the BONO increases. This result points out that there is no loss of the complexing ability of the grafted crown ether and that the complexes formed are similar to the complexes with the small macrocycle. 

One approach to achieve this slower reaction is to complex the silver ion with an appropriate reagent such that the rate of silver-polymer formation should be retarded, and consequently its desired unimolecular decomposition will be more controlled. The crown ethers are species capable of such complexation. The rate of appearance of silver metal is an inverse function of the stability of the silver-crown ether complex. 

Crown ethers and their derivatives have gained attention for their ability to form stable complexes with metal ions. The selective complexing properties of crown ethers towards metal ions have led recently to their incorporation into polymeric matrices. There are three main methods of crown ethers incorporation into polymer matrices. The first method is direct polymerization of the crown ether in a step-growth process, the second one is the polymerization through a chain-growth process, and the third one is post-functionalization of pre-formed polymers. 

The observed catalytic effect of the crown ether appears to be dependent on the nucleophile employed in both polymerization and corresponding model reactions. Not surprisingly, it appears that the stronger the nucleophile employed, the smaller the catalytic influence of the crown ether. For example, with potassium thiophen-oxide yields of polymer or model products were almost quantitative with or without catalyst. By contrast, the reaction of PFB with potassium phthalimide, a considerably weaker nucleophile, affords 6 in 50% with catalyst and in 2-3% without catalyst under identical conditions. However, it may be that this qualitative difference in rates is, in fact, an artifact of different solubilities of the crown complexed nucleophiles in the organic liquid phase. A careful kinetic study of nucleophilicity in catalyzed versus non-catalyzed reactions study is presently underway. 

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