Poly-borazines

Another example is the poly(borazine) chain, with repeat unit -BRNR-.53,65 The synthesis of tractable, unbranched polymers of this type is complicated by the formation of borazines, which are very stable cyclic molecules, [(RBRN)3], This problem can... 

Y. Kimura, Y. Kubo and N. Hayashi, High-performance boron nitride fibers from poly(borazine) preceramics. Composites Science and Technology, 51,173-179 (1994). 

A. Poly(/i-amino)borazines Prepared in a One-Step Process 156... 

D. Poly(/i-borylamino)borazines Prepared in a Two-Step Process 166... 

A. tris(Alkylamino)boranes-Derived Poly Z -(alkylamino)borazines]... 

Poly[/i-(alkylamino)borazines] can be prepared through a multistep thermolysis process involving tris(monoalkylamino)boranes of the type B(NHR)3 (R = Me, Pr ). Heating these molecular precursors under reduced pressure or in an inert atmosphere... 

In our research,16171819 we first prepared a series of tris(/i-alkylamino)borazines that possess different pendent groups. This allowed us to investigate the effect of the nature of the /i-(alkylamino) substituents on both the viscoelastic behavior of the thermal properties and, therefore, the melt spinnability of the resulting poly[/i-(alkylamino)-borazines] polymers. 

Table 1 Glass-Transition Temperatures and Ceramic Yields Measured for Poly[f -(alkylamino)borazines] 10, 9, 8, and 7... 

Poly[5-(alkylamino)borazines] 7-10 exhibited suitable viscoelastic and thermal stabilities to be extruded in the molten state through the monohole spinneret of a lab-scale melt-spinning apparatus. Thus, an extruded filament (diameter, 200 gm) was drawn with a windup unit, that is, a graphite spool. This provided green fibers with a wide range of diameters (16 =s (f> =s 50 gm Table 2), depending on polymer architecture. 

By analogy with B-trialkylaminoborazi ne and polyborazine derived therefrom, the first route envisioned to poly(borylaminoborazine) was the thermal condensation of molecular precursors under a convenient atmosphere. As detailed earlier the innovative idea behind this procedure is to tailor the polymeric precursor structure by increasing the distance between the two borazinic rings. For that purpose, we explored... 

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