Hyperbranched Polycarbosilanes and Polycarbosiloxanes via Hydrosilylation Polymerization

As pointed out in Chapter 1, silicon chemistry offers a variety of quantitative, high yielding reactions, i.e. hydrosilylation, Grignard reactions and controlled condensation of silanols that are suitable for the synthesis of organic-inorganic hybrid materials. Thus, silicon-based chemistry played a prominent role in the evolution of dendrimer chemistry [1–4], and it did not take long until the first examples of silicon-containing hyperbranched polymers were reported. Hyperbranched polymers are generally prepared by one-pot polymerization of AB_x (x ≥ 2) (see also Section 1.2) monomers and are characterized by polydispersity as well as a randomly branched structure due to the multifunctional polycondensation or polyaddition process. The statistical treatment of such polyfunctional polycondensations was achieved in the early 1950s by Flory, who calculated both molecular weights and polydispersity in such systems, as is discussed in Section 13.3 of this chapter [5, 6]. The properties of hyperbranched polymers are significantly different from their linear analogs and are characterized by good solubility, low viscosity and a large number of end-groups that can be used for further functionalization. Despite imperfections in branching and structure of hyperbranched polymers compared to monodisperse dendrimers, these properties render them easily accessible competitors for dendrimers, particularly in applications where structural perfection is not a mandatory prerequisite.