Evaluation of the synthesis of polysilanes by the reductive-coupling of dihaloorganosilanes

The blue color that develops during the alkali metal-mediated reductive-coupling of dihaloorganosilanes to form polysilanes has been shown to arise from colloidal alkali metal particles. The development of the color is demonstrated to mark the end of reaction, and the role that the colloid particles play in determining the proportion of very high molecular weight polymer that develops in these systems is discussed. The overall polymodal molecular weight distributions that result are explained in terms of an anionic mechanism of polymerization and the heterogeneous reaction conditions. Oligomeric materials that are always present in the product mixtures are shown to arise from alkali metal-induced polymer degradation reactions and from otherwise unreacted monomer that is consumed during the polymer isolation procedure. The problems of the reproducibility and control of such preparative methods are assessed in the light of these conclusions.