Hyperbranched polymers, organometallic

Another application of hyperbranched polymers as supports for catalysts is their use as backbones for the covalent attachment of organometallic fragments. NCN-pincer complexes (NCN-pincer = 2,6-bis[(dimethylamino)-methyl] phenyl anion) are attractive building blocks for catalytic reactions [20,21], Covalent introduction of the transition-metal complexes can also be of interest for visualization and imaging of dendritic polymers by transmission electron microscopy (TEM). 

In order to directly synthesize organometallic hyperbranched polymers, all the above described established methods could be utilized to knit metal-containing monomers together, provided they are stable under the applied polymerization conditions and do not interfere with the reaction mechanism. As an alternative, suitable pure organic hyperbranched polymers can be functionalized with organometallic complexes. Both approaches have been utilized by other research groups and will be briefly reviewed at the beginning of Chapters 3 and 4. 

Although a wide range of methodologies exist for the preparation of hyperbranched polymers, examples of metal-containing materials— which are directly synthesized from organometallic monomers— are very limited. Reinhoudt and coworkers reported the preparation of hyperbranched polymers via self-assembly of an... 

While A-B-A with composed alkylene dioxythiophene monomeric A units can be polymerized oxidatively to the corresponding polymer, linear (AB) and star branched polymers have to be made by organometallic reactions due to a low reactivity of the B unit. (AB) polymers with EDOT as the A unit and phenylene (Vlf) as well as fluorene (Vlg) structures as the B unit were synthesized by Suzuki polycondensation and show electrochromic behavior without any conspicuous properties. On the other hand, hyperbranched polymers with an additional triarylaminic core unit and similar composed branches made from 3,4-ethylenedioxythiophene and didodecyloxybenzene structures exhibited multicolor electrochromism to produce the three basic colors in the RGB system red, green, and blue. 

Some of these pol)miers exist as unusual colloid-like aggregates. Some organometallic hyperbranched polymers were found to aggregate even at very... 

Scheme 7 Synthesis of hyperbranched organometallic polymer from AB2-type monomer...

Recently, Abd-El-Aziz and colleagues reported different hyperbranched poly(arylethers) (4,5) and poly(arylthioethers) (6) containing cyclopentadienyliron moieties, which were successfully furnished by nucleophilic substitution of A + Bj type monomers (Scheme 2.3) [54], The polymers were thoroughly characterized by standard spectroscopic analysis techniques, they exhibited generally low viscosities, and the organometallic complexes were stable up to 230 °C, as evaluated by thermal gravimetric analysis (TGA). 

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