Copolymerization cluster containing monomers

Figure 4-12. Scheme of chain transfer in copolymerizations of cluster-containing monomers. 

In reeent years, methods for synthesizing such catalysts through copolymerization of cluster-containing monomers with common monomers have been elaborated (see Chapter 4). In these cases the exact ratio metal-functional group is determined during the catalyst preparation stage. High activity and selectivity in the action of such catalysts may be expected. 

Well-defined nanoclusters (w 10-100 A diameter) of several metals have been prepared via the polymerization of metal-containing monomers. The synthetic approach involves the block copolymerization of a metallated norbornene with a hydrocarbon co-monomer which is used to form an inert matrix. Subsequent decomposition of the confined metal complex affords small clusters of metal atoms. For example, palladium and platinum nanoclusters may be generated from the block copolymerization of methyl tetracyclododecane (223) with monomers (224) and (225) respectively. 10,611 Clusters of PbS have also been prepared by treating the block copolymer of (223) and (226) with H2S.612 A similar approach was adopted to synthesize embedded clusters of Zn and ZnS 613,614... 

Remarkably, the tolerance of the M(CH/-Bu)(NAr)(0/-Bu)2 catalysts (M = W or Mo) for functionalities allowed them to be used to effect ring-opened polymerization of norbornenes containing metals. Such monomers have already been copolymerized with norbornene or methyltetracyclododecene, to obtain semiconductor clusters of controlled cluster dimensions. A first block copolymer containing lead (e.g., 86) was prepared from norbornene and (C7H9CH2C5H4)2Pb in the presence of Mo(CHr-Bu)(NAr)(Ot-Bu)2 (Ar = 2, 6-C(,Hii-Px2) [59]. 

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