Pendant crown polymers

Montanari and coworkers have been particularly active in this area. They have generally utilized crowns or cryptands having long arms attached to them. These lipophilic arms are typically terminated in a primary or secondary amino function which may serve as a nucleophile in the reaction with a chloromethylated polystyrene residue. 

A typical system is a chlorome thy late d polystyrene resin cross-linked with 2 or 4% p-divinylbenzene and different amounts of chloromethylated sites (0.7—3.7 mequiv. of Cl per g of polymer) . The reaction is shown schematically in Eq. (6.19) and additional information may be found in Sects. 8.3 and 8.8. 

Blasius and coworkers have offered a somewhat different approach to systems of this general type. In the first of these, shown in Eq. (6.20), he utilizes a hydroxymethyl-substituted 15-crown-5 residue as the nucleophile. This essentially similar to the Mon-tanari method. The second approach is a variant also, but more different in the sense that covalent bond formation is effected by a Friedel-Crafts alkylation. In the reaction 

Before leaving consideration of this group of compounds, mention should be made of one unusual species of this general class. Tabushi, Kobuke and Nishiya have reported a polymer-bound hexaketone, illustrated below as compound 29, which is apparently of use in binding uranyl (UO2++) ions. The polymer has, in fact, been utilized in extraction of the uranyl ion directly from seawater . 

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Several examples have recently been reported of vinyl-substituted crowns that were polymerized under anionic conditions to pendant crown polymer systems <2002MM2432, 2002PLM3469, 2005PB237>. Typical examples of... 

With the success of CgK in the syntheses of 41 and related co-polymers, the same methodology was applied to the synthesis of polysilanes bearing pendant crown ether substituents, viz. 42-44,150,151 which were synthesized in yields from 6% to 28%, with molecular weights of the order of 104. The polymers were found to be water soluble and thermochromic in accordance with the Schweizer thermochromism theory (see Section 3.11.5.2.4).152... 

Fig. 24. Photodimerization of cinnamoyl group bearing polymer pendant crown-ethers...

When the pendant crown ether groups bind metal ions, the phase separation temperature is expected to rise because the hydrophilicity of the polymer increases. The concentration change of special metal ions in solution can be detected as the phase transition of the polymer solution, or the conformation change of the polymer chain. 

Fig. 6. Isothermal phase transitions from the phase separated to homogeneous state of the aqueous solution of the copolymer containing 11.6 mol % pendant crown ether groups by the addition of (O) potassium and (9) sodium chlorides at 32 °C and 37 °C. Polymer concentration was 1 mass %...

Baumann,T. E Reynolds, J. G. Fox, G. A., Polymer pendant crown thioethers synthesis and Hg(II) extraction studies of a novel thiacrown polymer. Chem. Commun. 1998,1637, and references therein. 

ION-BINDING PROPERTIES OF NETWORK POLYMERS WITH PENDANT CROWN ETHER LIGANDS... 

SELECTIVE CATION BINDING BY POLYMERS WITH PENDANT CROWN ETHERS... 

Polymers with pendant crown ethers show different selectivity from their monomers in complex formation with metal cations due to the ease of a 1 2 complex formation. They can be prepared either by the polymerization of the crown vinyl monomers or by the polymer reaction. The former method is preferable for studies on basic properties since it gives a regular polymer with pendant crown ether, however, the latter one is advantageous from an economic standpoint. 

Poly(methylsilylene-/>-phenylene)s carrying Si-linked benzocrown ether and ethoxy pendant groups 86 (parameters x and y are associated with the benzo crown vs. ethoxy ratio present in the polymer) showed ionochromic behavior, and responded selectively to alkali and alkaline earth metal ions in the emission spectra, depending on the crown ether ring size. These polymers also display solvatochromic properties by changing the solvent polarity in the absence of metal ions <2006OM2225>. 

Acrylate polymers containing crown-ether pendants have been synthesised as shown in Scheme 8 [178]. This polymer forms complexes with LiCl04. However, the conductivity observed is quite low. 

Commonly, polymers with a poly(siloxane) backbone and pendant side chain liquid crystalline groups are used. The side chain liquid crystalline groups are organic complexes with zinc, nickel, or crown ethers. This type of polymers is addressed as mesomorphic poly(siloxane). Side chains based on 4-biphenyl-4-allyloxybenzoate exhibit a special separation performance for racemic compounds. ... 

Treatment of a number of covalent polymers substituted with molecular recognition capability with suitable guests leads to chiral induction. The same crown ether-amino acid complementary pair described for the rosettes above was employed in the form of crown-ether pendant cis-transoidai poly(phenylacetylene). When the achiral polymer is treated with amino acids (in the form of their hydroperchlorate salts in acetonitdle) a large induced CD signal is observed in the backbone of the polymer. The polymer is sensitive to small enantiomeric excesses in the amino acid, as little as 0.005% enantiomeric excess of alanine can be detected. In a similar vein, c/5-transoidal poly(carboxyphenylacetylene) shows induced circular dichroism when treated with nonracemic chiral amines In addition, the system displays chiral memory, in that treatment of the complex with achiral amino alcohols results in retention of the chiral polymer backbone. 

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