Organosilicon dendrimers and hyperbranched polymers have proved to be highly versatile materials. We have authored or co-authored several reviews on these interesting compounds.
In 1998, we were the first group to report the synthesis of dendritic carbosilazanes such as that shown to the right. The synthesis involved a series of alternating hydrosilylation and nucleophilic substitution steps. We also succeeded in making small branched silazanes, potential cores for dendritic silazanes.
In 2009, we reported the synthesis of carbosilane-thioether dendrimers, a new class of organosilicon dendrimers, using thiol-ene chemistry. Click here for our research in thiol-ene chemistry.
We have also synthesized a series of hyperbranched organosilicon polymers from AB2 and AB3 monomers. Propagation occurs in high yield through Pt-catalyzed hydrosilylation or nucleophilic substitution reactions. Some of our monomers are shown below.
Methyldiethynylsilane is a particularly interesting monomer to us, as the resulting hyperbranched polymer possesses excess ethynyl groups located throughout the structure. On heating to ~200°C, the ethynyl groups crosslink and subsequent heating to 1300°C under an inert atmosphere results in only a 10-15% weight loss.
The ethynyl groups can also be chemically functionalized. Our research efforts were somewhat limited by the difficulty and expense involved in synthesizing methyldiethynylsilane.
In our published report, the synthesis involved a 72h reaction at 30° in the presence of Kryptofix® 222, an expensive catalyst. Yields were typically around 50%. However, in early 2008, graduate student Chinwon Rim discovered a new method in which we could make the monomer in 2h at room temperature without the catalyst (unpublished). The yield increased as well, as we can now reproducibly obtain pure monomer in 60-65% yield.
Our efforts are again focused on this monomer, and we are now exploring polymer functionalization reactions as well as additional modes of polymerization.