Carbosilanes block

Matsumoto K, Matsuoka H (2005) Synthesis of core-crosslinked carbosilane block copolymer micelles and their thermal transformation to silicon-based ceramics nanoparticles. J Polym Sci A Polym Chem 43(17) 3778-3787... 

ADMET is quite possibly the most flexible transition-metal-catalyzed polymerization route known to date. With the introduction of new, functionality-tolerant robust catalysts, the primary limitation of this chemistry involves the synthesis and cost of the diene monomer that is used. ADMET gives the chemist a powerful tool for the synthesis of polymers not easily accessible via other means, and in this chapter, we designate the key elements of ADMET. We detail the synthetic techniques required to perform this reaction and discuss the wide range of properties observed from the variety of polymers that can be synthesized. For example, branched and functionalized polymers produced by this route provide excellent models (after quantitative hydrogenation) for the study of many large-volume commercial copolymers, and the synthesis of reactive carbosilane polymers provides a flexible route to solvent-resistant elastomers with variable properties. Telechelic oligomers can also be made which offer an excellent means for polymer modification or incorporation into block copolymers. All of these examples illustrate the versatility of ADMET. 

Fig. 4.44 Carbosilane dendrimer assembled from thiophene building blocks (according to Nakayama et al.)...

A first-generation carbosilane dendrimer consisting of 16 thiophene rings could be isolated in 19% yield, albeit together with various by-products in comparable amounts [85]. The synthetic building block methyl tris(2-thienyl)silyl ether was first prepared from tetramethoxysilane and an excess of thienyl-lithium (Fig. 4.44). 

It is important to end-cap the living carbosilane polymer with 1,1 -diphenylethylene to decrease the reactivity of the living center in order to obtain the block copolymer successfully. The diphenylethylene thus provides a milder carbanion for initiation of the methacrylate monomer. With this modification, efficiency of the end-capping by an electrophile (quenching) has reached 0.95 <2001PSA86, 1998PSA2699>. 

PEO formed a surface while the hydrophobic carbosilane dendritic block was incorporated into the micelle core. Micellar characteristics were determined using fluorescence techniques and dynamic light scattering. Copolymers with a third-generation dendritic block could not be dispersed in water. 

We have described a new system of polymeric snpports based on multifunctional, exceptionally sterically hindered carbosilane moieties, grafted with block poly(vinylmethyl-co-dimethyl)siloxane arms. They offer uniformly periphery-distribnted active sites (-CH = CH moieties) and can be used for preparation of novel catalysts. Platinum was thus attached to the polymers via coordination to vinyl gronps. The materials used in hydrosilylation of vinylsilanes can be considered as an alternative for traditional platinum catalysts. The utility of the catalysts seems to be dependent on the ratio [D]/[V] in the copolysiloxane arm. Those with too high amonnt of vinyl groups suffer from poor solubility and catalytic performance dne to excessive inter/intra-chain coordinative cross-linking. 

Terunuma and coworkers reported the properties of a different type of carbosilane dendrimer (Nq = 3, Wb = 3) bearing either cyanobiphenyl species or an optically active unit derived from 2-phenylpyrimidine at the periphery (Fig. 15). Only three branches emanated from the central silicon atom, the fourth valency being blocked by a phenyl group leading to 3 (GO), 9 (Gl), and 27 (G2) terminal functional units. 

Carbosilane dendrimers containing titanium and zirconium complexes on their periphery have been prepared and used in olefin polymerization reactions.Generally, the best synthetic route to these materials involves the synthesis of generations of suitably functionalized dendrimers to which the metal is added in the final step giving products such as 276. Routes involving the incorporation of pre-metallated building blocks gave only low yields of the desired dendrimers. 

Pd complexes of soluble P,0-fimctionalized carbosilane dendrimers (8) were used by Vogt and co-workers for the hydrovinylation reaction (codimerization of ethylene and styrene). This C-C coupling reaction is of great interest, because it opens an easy access to building blocks for fine chemicals as well as pharmaceuticals [Eq. (6)] [16]. 

Design and synthesis of hybrid polymers and of dendrimers for special applications and as building blocks for carbosilanes, polysilanes catalysis and highly crosslinked coatings. 

Keith, C. Reddy, R. A. Hahn, H. Lang, H. Tschierske, C. The carbosilane unit as a stable building block for liquid crystal design a new class of ferroelectric switching banana-shaped mesogens. Chem.Commun. 2004,18, 1898-1899. 

Carbosilane Dendrimer Synthesis. is also used as a building block for the preparation of carbosilane dendrimers. The preparation of these dendrimers follows the method of van der Made, which involves alternating cycles of platinum-catalyzed hydrosilylation of a terminal alkene with a chlorosilane and alkylation of the resulting chlorosilane with allylmagnesium bromide. The first step in the preparation of the dendrimeric structure involves the hydrosilylation of with dichloromethylsilane in the presence of platinum on carbon as the catalyst. This process introduces a methyldichlorosubstituent on each of the four vinyl groups to afford 7 in excellent yield (eq 5). 

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