Borazine-based polymers

Borazine is an important and well-studied inorganic heterocyclic ring. It is isoelectronic with benzene and has been known as inorganic benzene (5.23). 

Interest in borazine-based polymers arises out of their possible utility as precursors for the preparation of boron nitride, a high value ceramic material. It was discovered that borazine readily undergoes a dehydropolymerization at 70-110 °C to afford a soluble polymer, polyborazylene, in about 80-90% yield (see Eq. 5.15) [30, 31]. 

Recently, modified polyborazylenes have been prepared by reactions with secondary amines containing alkyl chains such as diethylamine, dipentylamine as well as silyl amines such as hexamethyldisilazane (see Eq. 5.16) [32]. 

Modified polyborazylenes have better solubility properties than the parent polyborazylene. Also, these new versions of polyborazylenes are melt-spinnable and have been shown to afford boron nitride ceramic fibers on thermal treatment [33]. 

Allcock HR, Coley SM, Manners I, Visscher KB Parvez M, Nuyken O, Renner G (1993) Inorg Chem 32 5088 

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Processable boryl-borazine based polymers. An alternative approach was undertaken in order to prepare polyborazines with multi-atom bridges between the rings. The reaction of 2,4,6-trichloroborazine with BfNHPr h yields a polymer (3) in which the borazine rings are connected through N-B-N bridges (Scheme 3). 

PAINE SNEDDON Recent Developments in Borazine-Based Polymers 359... 

Alternative synthetic approaches to Si-B-C-N-H polymers starting from functionalized borazine derivatives were published by Srivastava et al. " and Haber-echt et al." Srivastava et al. published a method for synthesizing a soluble borazine-based Si-B-C-N-H polymer by reacting B-chloroborazines with LiSi(Si(CH3)3)3 followed by subsequent polymerization with hexamethyldisilazane. 

SCHEME 18.25 Synthesis of borazine-based Si-B-C-N-H polymers by hydrosilylation of B-triethynylborazine with trichlorosilane and subsequent hydrogenation with LiAlH4 or aminolysis with methylamine, respectively." - 2 ... 

Borazine-based Si/B/N/C polymers have been obtained by polycondensing H3N3B3(Cl)2Si(SiMe3)3 with hexamethyldisilazane [88]. Here once again silazane cleavage, forming the volatile chlorotrimethylsilane as a byproduct, is the driving process. 

To improve the thermal durability and inflammability of the materials, we have been investigating organoboron structures to hybridize with silicon polymers. In this field, the preceramic character of the borazine structure [2] and its catalytic function for anti-oxidation [3] are already known. Lately Chujo reported hydroboration polymerization to obtain boron-based polymers [4]. 

Borazine Based Preceramic Polymers for Advanced BN Materials... 

Because of the difficulties encountered for handling borazine due to its high reactivity and volatility at room temperature, very few efforts were devoted to the preparation of borazine-based preceramic polymers. Sneddon et al. have demonstrated that polymers derived from borazine, namely polyborazylenes, could be... 

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