Ring structures polysilazanes

They find that heating cyclotri- and cyclotetrasilazanes with ammonium halide catalysts at temperatures of 160°C for 6-8 h results in a condensation polymerization process that evolves ammonia and leads to the formation of waxy polysilazanes. Analytical results suggest that these polysilazanes consist of rings linked by silyl bridges as illustrated by the following structure ... 

Consider the effects of the N-R group on the structure and reactivity of polysilazanes as susceptible to hydrogen bonding effects. These effects alone should favor ring closure over the respective siloxane analogs. Moreover, for R = H, a new type of depolymerization reaction, analogous to reaction (4), is available as illustrated in reaction (35). Thus, reaction (35) could also contribute to the... 

A general formula for the polysilazane obtained is [CH3(CH3NH)Si(CH3N)]jc [CH3Si(CH3N)i.5]y, and its chemical structure is considered branched, partly incorporating a ring stmcture. 

Polysilazanes represent another important class of ceramic materials that contain N-Si-N and C-Si-N units, sometimes wifli or without oxygen. The structural forms of polysilazanes may be chains, rings, crosslinked networks, or, more recently, dendrimers. Generally, the prepolymers contain sihcon bonded to nitrogen in the backbone and organic groups or hydrogen as substituents on Si and N (65). 

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