Molecular weight organometallic polymers

Since the yield in the oxidative coupling is practically quantitative, the oxidative polymerization of a,( )-diethynyl monomers would be expected to yield high molecular weight, linear polymers, as shown in equation (18). Hay has reported that almost any diethynyl monomer, even organometallic monomers, can be polymerized to high molecular weight polymers in Ae presence of a soluble amine complex catalyst of a copper(I) salt (Hay modification). ... 

Segal, S. Goldberg, I. Kol, M. Zirconium and titanium diamine bisfphenolate) catalysts for a-olefin polymerization From atactic oligomers to ultra-high molecular-weight isotactic polymers. Organometallics 2005, 24, 200-202. 

Development of more efficient transition metal catalyst systems including using novel and efficient ligands has been one of the focuses in organometallic chemistry.35 The developments in this area will allow not only to synthesize polymers under mild conditions with higher or desired molecular weights but also to use less expensive, more readily available materials for the polymerizations. 

One previous synthesis of ferrocene-containing condensation polymers via interfacial methods at room temperature has been reported by Knobloch and Rauscher, who formed low molecular weight polyamides and polyesters by reacting l,l -bis(chloro-formyl)ferrocene with various diamines and diols. Further, Carraher and co-workers have utilized interfacial techniques in the formation of other types of organometallic polymers. 

Since the properties of a polymer can be noticeably influenced by small variations in the molecular structure, and these in turn depend on the preparation conditions, it is necessary when reporting data to indicate not only the type of measurement (e.g., molecular weight by end group analysis crystallinity by infrared measurement or by X-ray diffraction etc.), but also the type of preparation (e.g., radical polymerization in bulk at 80 °C polymerization with a particular organometallic catalyst at 20 °C). 

Alkynyl halides are possible monomers for the cross-coupling polymerization, in which boronic acids are used as the organometallic counterparts. For example, bifunctional boronic acid 46 is allowed to react with l,4-di(bromoethy-nyl)benzene 138 to afford the corresponding PAE 139 as shown in Equation (64). Polymerization proceeds at room temperature in toluene in the presence of silver(i) oxide as an activator of the boron reagent. The polymer 139 is obtained in 30-50% yield showing color of red-brown to deep red-brown and slight solubility in toluene (<0.1 wt.%). The molecular weight (Mr of 139 was 1700-4300 (PDI = 1.3-3.6). 

This diversity of sites explains why the molecular weight distribution (MWD) of polymers produced by Cr/silica is broad (71). Model calculations which assume a single type of active site usually predict Mw/Mn 2,4 but in reality Mw/Afn = 6-15 is common, and 20-30 can be achieved with catalyst modifications. The distribution is also broader than that generally obtained from Ziegler catalysts, for which Mw/Afn = 3-6 under similar conditions. Experience with organometallic compounds suggests that a broad MWD may be a general feature of catalysts which terminate by -elimination. 

Polymers with much higher average molecular weights, from 90,000 to 4 x 106, are formed by a process of coordinate anionic polymerization (43—45). The patent literature describes numerous organometallic compounds, alkaline-earth compounds, and mixtures as polymerization catalysts. Iron oxides that accumulate in ethylene oxide storage vessels also catalyze polymerization. This leads to the formation of nonvolatile residue (NVR) no inhibitor has been found (46). 

Higher molecular weight polymers (40,000-50,000) have been reported from condensation reactions between monomer 6.15 and various silanediols, as illustrated in reaction (6).2 Polymer 6.16 can be melt-fabricated into films or fibers, which probably reflects the presence of roughly 100 repeating units per chain. However, the separation of the ferrocenyl units by the organic linker groups reduces the influence of the organometallic component. 

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. 

Organometallic macro cycles and cyclic polymers were prepared by the photolytic ring opening of a silicon-bridged ferrocenophane with a bipyridine initiator. The relative amounts of cyclic oligomers and cyclic polymer, as well as the molecular weight of the cyclic polymer, can be controlled by the reaction temperature [228]. 

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