Silazanes ring-opening

Cyclosilazanes are found to be reluctant to polymerize by the ring-opening process, probably for thermodynamic reasons. On the other hand, six- and eight-membered silazoxane rings are able to undergo anionic polymerization under similar conditions to those which have been widely used for cyclosiloxane polymerization provided there is no more than two silazane units in the cyclic monomer. They can also copolymerize with cyclosiloxanes however, the chain length of the linear polymer formed is substantially decreased with increasing proportion of silazane units. 

The reactions of vinylcyclosiloxanes and vinylcyclosilazanes with styrene in the presence of RuHCl(CO)(PCy3)2 opened a new route to functionalized monomers for the ring-opening polymerization of cyclosiloxanes and cyclo-silazanes (Eq. 29) [56]. 

Bostick, E. E., Cyclic Siloxanes and Silazanes, Chap. 8 in Ring-Opening Polymerization, K. C. Frisch and S. L. Reegen, eds., Marcel Dekker, New York, 1969. 

Several reports on copolymerization of cydosilazanes with other monomers have been published. A series of new poly (siloxane)s and poly(silazane)s were synthesized by cationic ring-opening copolymerization of the cydic monomers, octa-methylcydotetrasiloxane and hexamethylcydotiisilazane, obtaining PDMS-poly(dimethylsilazane) copolymers with different concentrations of the comonomer units. The polymers were thermally cured and pyrolyzed, produdng ceramic materials. ... 

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