Metal Bond-Containing Polymers

Finally, it is noted that chromophores other than CO have been incorporated into polymer backbones to make the polymers photodegradable. An example is the class of polymers with metal-metal bonds along the polymer backbones. Photochemical degradation occurs with these polymers because metal-metal bonds cleave homolytically when irradiated with visible light (Eq. 7 scheme 7) The remainder of this review focuses on these materials. 

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The analogous strategy for synthesizing metal-metal bond-containing polymers also uses difunctional, cyclopentadienyl-substituted metal dimers. A sample step-growth polymerization reaction is shown in equation 3, which... 

Although the resolution of this lithographic method by current standards is somewhat low, this method nevertheless demonstrates that metal-metal bond-containing polymers may be useful in applications where reversible imaging is needed and where the image can be made permanent if need be. Because this example is the only example of reversible lithography using polymers of this type, further study would seem to be called for. 

This step polymerization strategy is quite general, and a number of metal-metal bond-containing polymers have been made from monomers containing functionalized Cp ligands. ... 

The metal-metal bond containing polymers (generically shown in scheme 7) photolyze according to the mechanism in scheme 12, and it is expected that the... 

Synthetic Strategy. Our syntheses of the metal-metal bond-containing polymers am based on the known chemistry of polymeric ferrocenes (d-i2). Ferrocene is incorporated into polymers by substituting its Cp rings with appropriate functional groups and then reacting with appropriate difunctional organic monomers (e.g , equation 3). 

Polymers containing all metal backbones of Ru-Ru or Os-Os bonds have been prepared via the electrochemical reduction of ruthenium and osmium complexes containing /ram-chloride ligands.81,82 Scheme 2.6 shows the synthesis of polymers with their backbones comprised solely of metal-metal bonds. The polymers were prepared by reducing [Mn(/ran.s-Cl2)(bipyXCO)2] (M = Ru, Os), 33, to M° complexes and forming the polymer after the loss of the chloride ligands. In both cases, the polymers were selective for the reduction of carbon dioxide. 

Scheme 2.7 shows the synthesis of organomolybdenum polymers containing metal-metal bonds.83 Polymer 36 was prepared via reaction of trans-Mo(CO)3Cl containing t)5-Mo complexes with MeMgCl. They displayed poor solubilities. 

It is noticeable that cross-metathesis with the unfunctionalised alkenes occurred in significantly higher yields over shorter reaction times and required a smaller excess of the soluble alkene. This was possibly due to the unfunctionalised alkenes, which are more nucleophilic than their ester containing counterparts, complementing the less nucleophilic/more carbon-metal bond stabilising allylglycinol 18. Comparable results were obtained from cross-metathesis reactions of the polymer-bound isomeric N-Boc C-allylglycinol with the same four alkenes. 

These novel carbon nanostructures can also be modified by (a) doping, that is the addition of foreign atoms into the carbon nanostructure, (b) by the introduction of structural defects that modify the arrangement of the carbon atoms and (c) by functionalization involving covalent or noncovalent bonding with other molecules. These modifications opened up new perspectives in developing novel composite materials with different matrices (ceramic, polymer and metals). For example, polymer composites containing carbon nanostructures have attracted considerable attention due to... 

Chlorine-containing polymers such as poly(vinyl chloride) PVC undergo an autocatalytic dehydrochlorination reaction under the influence of elevated temperature and UV radiation. Since the HCl originating from the dehydro chlorination of the PVC chains is believed to sustain this autocatalytic process, stabilizers that irreversibly bond HCl can thus inhibit the degradation. Heavy metal compounds such as cadmium stearate or lead stearate are currently used for this purpose. However, alternatives are required due to environmental problems associated with the use of heavy metals. Indeed, the largest current application of LDH materials is in the polymer industry, mainly to stabilize PVC [3,229-232]. 

Cycloalkenes undergo ring-opening polymerization in the presence of coordination initiators based on transition metals to yield polymers containing a double bond, for instance, cyclo-pentene yields polypentenamer [IUPAC poly(pent-l-ene-l,5-diyl)] [Amass, 1989 Cazalis et al., 2000, 2002a,b Claverie and Soula, 2003 Doherty et al., 1986 Ivin, 1984, 1987 Ivin and Mol, 1997 Ofstead, 1988 Schrock, 1990, 1994 Tmka and Gmbbs, 2001], The... 

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