Carbosiloxane, hyperbranched

Like monodisperse carbosiloxane dendrimers, hyperbranched carbosiloxanes can be produced by hydrosilylation [100]. The first compounds of this kind were synthesised in 1991 by Mathias and Carothers [101] by polymerisation of an al-lyl-tris(dimethylsiloxy)silane monomer with addition of chloroplatinic acid hydrate (Fig. 4.52). The reaction proceeds relatively fast however, addition of more catalyst does not increase the molecular masses (19000 g/mol). The NMR spec-... 

Fig. 4.52 Hyperbranched carbosiloxane (according to Mathias and Carothers). Some of the monomeric building blocks are shown with a grey background for the sake of illustration...

In 1994, Rubinsztajn reported the hyperbranched hydrosilylation polymerization of the AB3 carbosiloxane monomers 9 and 10181. Since intramolecular cyclization of these monomers would lead to more highly strained five-membered rings, it was expected that intermolecular reaction would be preferred. This was indeed the case, and molecular weights were highest when polymerizations were performed in bulk. Furthermore, slow addition of monomer resulted in polymers of much higher molecular weight. Functionalization of the polymers could be performed via hydrosilylation reactions, although these... 

Herzig and Deubzer also reported the slow monomer addition process in the formation of hyperbranched poly(carbosiloxanes)188. In this report, they added vinyltris(dimethyl-siloxyjsilane (9) (previously reported by Rubinsztajn181) to various cores (16, 17 and 18). A dependence of polymer molecular weight on overall amount of monomer added was established by viscosity measurements. In addition, the formation of small cyclic compounds was reported and quantified. 

Hydrosilylation is not the only reaction available for the preparation of hyperbranched poly(carbosiloxanes). In a recent report, Weber and Londergan described the preparation of hyperbranched poly(carbosiloxanes) by ruthenium-catalyzed addition of ortho C—H bonds across terminal double bonds (Scheme 26)190. Depending on reaction conditions, soluble or insoluble polymers could be obtained. NMR endgroup molecular weight analysis of the soluble polymer gave a value of 12,200. The structure of the polymer was established with XH, 13C and 29Si NMR analysis. 

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