Organometallic units, polymers

The advantage of these polymers over poly(vinylferrocenes) or related species with pendent organometallic units is that the condensation polymers have ferrocene units in the main chain where they can exert their maximum influence on polymer thermal stability. The disadvantage of the condensation products is that, except in the last example, the molecular weights are too low to favor fiber or flexible film formation. Nevertheless, this work indicated the potential usefulness of polymers with metallocene units in the main chain. 

The disulfide links in the organometallic ferrocene polymers can be reductively cleaved, as in other disulfide-connected structures such as proteins, and the iron centers can be oxidized electrochemically to give ferrocenium units [273] both these redox processes are reversible in principle. 

Metal-containing polymers may be produced by various methods, such as chemical reactions of precursors— in particular, reactions of metal salts in polymer solutions, the treatment of polymers with metal vapors, or the polymerization of various metal-monomer systems [1-4], Depending on the metal nature and the polymer structure, these processes lead to organometallic units incorporated into polymer chains, metal-polymer complexes, or metal clusters and nanoparticles physically connected with polymer matrix. Of special interest are syntheses with the use of metal vapors. In this case, metal atoms or clusters are not protected by complexones or solvate envelopes and consequently have specific high reactivity. It should be noted that the apparatus and principles of metal vapor synthesis techniques are closely related to many industrial processes with participation of atomic and molecular species [5]—for example, manufacturing devices for microelectronic from different metals and metal containing precursors [6]. Vapor synthesis methods employ varying metals and... 

The R group can be an alkoxy, aryloxy, amino, alkyl, heterocyclic ring or an inorganic or organometallic unit. Allcock and co-workers were the first who did study extensively the synthesis of poly[(organo)phosphazene] derivatives. Most polyphosphazene derivatives are prepared starting from a precursor polymer, poly[(dichloro)phosphazene]. A variety of polymers with variable properties can be prepared by nucleophilic displacement reactions (Allcock, 1972, 1979, 1986) (Figure 2). 

Metal-acetylide complexes have been used as a unit of organometallic polymers that have metallic species in the main chain [20]. Representative examples are metal-poly(yne) polymers (19) of group 10 metals depicted in Scheme 5. These polymers are easily prepared from M(PR3)2Cl2 (M=Pt, Pd) and dialkynyl compounds catalyzed by Cu(I) salts in amine. Recently, this synthetic method was successfully applied to the construction of metal-acetylide dendrimers. 

As a final example of catalytic hydrogenation activity with polymer-stabilized colloids, the studies of Cohen et al. should be mentioned [53]. Palladium nanoclusters were synthesized within microphase-separated diblock copolymer films. The organometallic repeat-units contained in the polymer were reduced by exposing the films to hydrogen at 100 °C, leading to the formation of nearly monodisperse Pd nanoclusters that were active in the gas phase hydrogenation of butadiene. 

The three phases that are present in the Ziegler-Natta polymerisation are (i) the monomer (ii) the solvent and (iii) the catalyst. Reactions take place at certain points on the surface of catalyst particles. The polymer molecule grows as the monomer units join the chain where earlier monomer is attached to the catalyst particle. The precise nature of the action of catalyst is not yet known. However, the first step in the polymerisation process proposed is the formation of a monomer-catalyst complex between the organometallic compound and the monomer. 

Polymer % organometallic Ratio of all/organo-metallic units pa n [%]... 

As surmized in a recent review article there are literally hundreds of polymeric systems featuring organometallic complexes within a conjugated organic backbone. Given recent reviews of these systems, here we shall restrict discussion to the various polymeric species and ceramic materials derived from diyne complexes and from coordination of metal fragments to polymers featuring C=CC=C repeat units. 

Other reactions of dienes with metal atoms are only of a limited synthetic use. Dibenzylideneacetone (PhCH=CH—CO—CH=CHPh DBA) reacts with palladium vapor to afford Pd2(DBA)3, a complex in which the coordination is through the two C=C units and does not involve the C=0 (5, 92). Cobalt vapor undergoes an extremely complicated reaction with 1,4-pentadiene, producing pentenes, C5H6, and various polymers as well as the organometallic product, HCo( 1,3-pen tadiene)2, which involves isomerization from a nonconjugated to a conjugated diene (104, 110). 

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