Cyclization in the synthesis of hyperbranched polymers

During the synthesis of hyperbranched polycarbosilanes, the polyaddition of the vinyl- and allyl silane monomers stopped at rather low molecular weights when the hydrosilylation reaction was not performed in bulk but in solution. A reduced possibility of polymer molecules to react with each other might in fact be explained by an increased probability of intramolecular addition of the terminal SiH group that competes with polymer-polymer addition. The largest degree of cyclization was to be expected for methyldivinylsilane because ring formation of a dyad yields a thermodynamically favored six-membered ring.