Polymer crosslinked coordination

Construction of organic nanotubes starting from porphyrin dendrimers with core/shell architecture is also feasible. Figure 8.29 also shows how covalent nanotubes can be produced by removal of the dendritic component of the molecule. A coordination polymer is first synthesised from a dendritic metallopor-phyrin with alkene end groups. This is subjected to intramolecular and intermo-lecular crosslinking by ring-closing metathesis at the periphery. 

The highly crosslinked, three-dimensional network structure of the Cr(III) coordination polymer is considerably more stable at elevated temperatures than the Zn(II) polymer or the other transition metal polymers which have been studied. For example, while the Cr(III) sample sustains a loss in weight of about 30% at 850°C., the Zn(II) coordination polymer loses 60% under similar conditions. 

A great variety of possibilities are available when a metal is part of a linear or crosslinked macromolecule (Section 1.2.1, Fig. 7-1). One possibility is the covalent incorporation of a metal into a homochain (metal-metal connections) or a heterochain (metal-heteroatom connections). Coordinative bonds between a metal ion and another coordinating donor group can lead to linear chains or to supramolecular organizations when coordination polymers are formed. n-Bonds between rt-rich aromatic compounds and metal ions can result in polymeric metallocenes. Covalent and coordinative bonds are realized in cofacially stacked metal complexes. In addition, dendrimers containing the interaction of metals and another group in different bonds are treated in this chapter. 

Wright examined the synthesis of different classes of chromium tricarbonyl-coordinated polymers. Poly(phenyl ethynyl)s coordinated to chromium tricarbonyl moieties (21, 23) were synthesized by palladium catalyzed cross-coupling of (r -l,4-dichloroarene)tricarbonyl chromium complexes with organostannane reagents (Scheme 4). ° Combustion analysis of these polymers indicated that their degree of polymerization was 18, which corresponds to a MW of 7800. Combustion and IR analysis of polymers that were heated above 200°C indicated that crosslinking reactions occurred followed by loss of carbon monoxide from the Cr(CO)3 moieties. 

The connection between polymer chemistry and ceramic science is found in the ways in which linear macromolecules can be converted into giant ultrastructure systems, in which the whole solid material comprises one giant molecule. This transformation can be accomplished in two ways—first by the formation of covalent, ionic, or coordinate crosslinks between polymer chains, and second, by the introduction of crystalline order. In the second approach, strong van der Waals forces within the crystalline domains confer rigidity and strength not unlike that found when covalent crosslinks are present. 

A major development in this area was brought about by the invention of crosslinked polystyrene-supported 9-(/)-chlorobenzoy 1 )quinine ligands 17 [54] and 18 [55], The salient feature of this invention is the connection of the quinine unit to the polymer backbone through a sterically undemanding spacer. Thereby, the quinuclidine, which in catalysis coordinates to osmium, is free of steric interaction with the polymeric side chain. Dihydroxylation of trans-stilbene in the presence of 17 and NMO as co-oxidant gave stilbene diol with 87% ee. However, changing the terminal oxidant to K3[Fe(CN6)] led to full inhibition of the reaction. This result was explained by a possible collapse of the polymer in the required protic solvent, which prevented substrate penetration. 

In vivo elastin fiber formation requires the coordination of a number of important processes. These include the control of intracellular transcription and translation of tropoelastin, intracellular processing of the protein, secretion of the protein into the extracellular space, delivery of tropoelastin monomers to sites of elastogenesis, alignment of the monomers with previously accreted tropoelastin through associating microfibrillar proteins, and finally, the conversion to the insoluble elastin polymer through the crosslinking action of lysyl oxidase (Fig. 2). 

Figure 11.2 Shape of relaxation maps (coordinates of transitions a, p, and y in a graph In (frequency) - reciprocal temperature). Left polymers having their a and p transitions well separated (example polycarbonate, amine-crosslinked epoxy). Right polymers with close a and p transitions (example polystyrene, unsaturated polyester).

When 8-hydroxyquinoline and derivatives of bis(8-hydroxy-quinoline) react with metal ions, coordination complexes and polymers are formed, respectively, which exhibit improved thermal stability. This paper reviews the reaction of first-row transition metal ions with such ligands and their effect on the stabilization of these organic molecules. For the polymers containing divalent Mn, Co, Ni, Cu, or Zn the decomposition temperature is related to the periodic properties of the metal as well as the composition of the ligand to which the metal is coordinated. Trivalent chromium produces a crosslinked polymer when it reacts with bis(8-hydroxy-5-quinolyl)methane, and the thermogram for this polymer is also reported. 

Critical temperature the temperature above which vapor cannot be liquefied, no matter what pressure is applied. (16.11) Crosslinking the existence of bonds between adjacent chains in a polymer, thus adding strength to the material. (22.5) Crystal field model a model used to explain the magnetism and colors of coordination complexes through the splitting of the d orbital energies. (20.6)... 

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