Polymers, cyclophanes

At first, the catalytic effect of the single micellar solutions based on surfactants of different structure was studied. The data covering this period are reviewed in refs. The regularities when generalized made it possible to proceed with the more complicated systems, in particular, the binary surfactant solutions, the polymer-surfactant and polymer-cyclophane (calixarene, pyrimidinophane, and etc.) systems. For these systems, the terms supramolecular systems (ensembles, compositions, complexes) are further used. 

Murakami, Y. Functionaiited Cyclophanes as Catalysts and Enzyme Models. 115, 103-151 (1983). Mutter, M., and Pillai, V. N. R. New Perspectives in Polymer-Supported Peptide Synthesis. 106, 119-175 (1982). 

A potential drawback of all the routes discussed thus far is that there is little control over polydispersity and molecular weight of the resultant polymer. Ringopening metathesis polymerization (ROMP) is a living polymerization method and, in theory, affords materials with low polydispersities and predictable molecular weights. This methodology has been applied to the synthesis of polyacctylcne by Feast [23], and has recently been exploited in the synthesis of PPV. Bicyclic monomer 12 [24] and cyclophane 13 [25) afford well-defined precursor polymers which may be converted into PPV 1 by thermal elimination as described in Scheme 1-4. 

After the discovery of the photopolymerization of 2,5-DSP crystals, several types of photoproducts were found, not only the linear polymers, but some other derivatives, e.g. the V-shaped dimer or cyclophane (Hasegawa and Hashimoto, 1992). The photopolymerization occurs in a step-growth mechanism by cyclobutane formation between the excited olefin and the olefin in the ground state. 

The reversible acid-catalyzed transacetalation of the cyclophane formal 3 has been shown to undergo a ring-fusion/ring-fission process to generate a mixture of polymer cyclic formaldehyde acetals by means of oxonium ion intermediates <06CEJ8566>. The stepwise... 

With these features in mind, we envisioned a new family of macrocyclic ligands for olefin polymerization catalysis (Fig. 9) [131, 132], We utilized macrocycles as the ligand framework and installed the catalytic metal center in the core of the macrocycles. Appropriate intra-annular binding sites are introduced into cyclophane framework that not only match the coordination geometry of a chosen metal but also provide the appropriate electronic donation to metal center. The cyclophane framework would provide a microenvironment to shield the catalytic center from all angles, but leaving two cis coordination sites open in the front one for monomer coordination and the other for the growing polymer chain. This could potentially protect the catalytic center and prevent it from decomposition or vulnerable side reactions. 

The closed structure of the cyclophane ligand also induces dramatic changes in the polymer microstructure. Polyethylene from the cyclophane catalyst 1.53a is considerably more branched than with catalysts bearing acyclic ligands, which suggests... 

The apparent binding constant K y obtained by Stern-Volmer quenching studies is the product of the number of receptors visited by the exciton and the binding constant of to the cyclophane receptor. For this reason polymer 3 and its monoreceptor model 2 were designed so that the binding constant for methyl viologen to the receptor was known for both systems. This allowed the calculation of the true amplification factor of 67. 

Scheme 4 Stacking of diolefin compounds and the formation of cyclobutane, cyclophane, and polymers as the photoproducts...

They found that some cyclophanes 82 exchanged rapidly between the polymer chain ends and solution relative to the NMR time scale. However, some of the cyclics 82 were trapped in the middle of polymer chain on the NMR time scale and were thus excluded from the exchange process. These two papers demonstrated that this type of self-assembly provides a very strong driving force for threading. 

Most of the reported polyrotaxanes are based on CD and crown ethers. Only a few polyrotaxanes are from other macrocycles, e.g. phenanthroline-based cyclics and bisparaquat cyclophane. Most CD-based polyrotaxanes were prepared by threading CD on to preformed polymers because CD are only soluble in polar solvents or water and not compatible with typical polymerization conditions. On the other hand, aliphatic crown ethers are soluble in water and most organic solvents. Therefore, they have broadened the scope of polyrotaxanes in terms of both polymerization conditions and types of backbones. They have often been threaded onto polymeric backbones by using them as solvents during polymerizations. 

Hydrophobic species bearing hydrocarbon chains present vitamin B12 or vitamin B6 type activity [5.37]. Such systems lend themselves to inclusion in membrane or micellar media. They thus provide a link with catalysis in more or less organized media such as membranes, vesicles, micelles, polymers [5.39-5.41] (see Section 7.4). Water soluble cyclophanes showing, for example, transaminase [5.42], acetyl transfer [5.43], pyruvate oxidase [5.44] or nucleophilic substitution [5.45] activity have been described. 

Keywords Crown compounds Liquid crystals Mesophases Metallomesogens Polymers Salt effects Self-assembly Substituent effects Supramolecular chemistry Phthalocyanines Cyclophanes... 

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