Boron-nitrogen-containing polymers

The recent interest in boron-nitrogen-containing polymers has spurred some renewed interest in borazine preparations since these compounds are potential monomers. The direct reaction between (ClBNHJs and NH3 produces an organic solvent insoluble polymer. In an attempt to control ammonolysis chemistry, the reactions of (Mc2NBNH)3 with... 

Boron- and Nitrogen-Containing Polymers for Advanced Materials 103... 

Boron-containing nonoxide amorphous or crystalline advanced ceramics, including boron nitride (BN), boron carbide (B4C), boron carbonitride (B/C/N), and boron silicon carbonitride Si/B/C/N, can be prepared via the preceramic polymers route called the polymer-derived ceramics (PDCs) route, using convenient thermal and chemical processes. Because the preparation of BN has been the most in demand and widespread boron-based material during the past two decades, this chapter provides an overview of the conversion of boron- and nitrogen-containing polymers into advanced BN materials. 

Phosphorus-boron-nitrogen-containing oligomer and polymer products comprising -P=0, -P-0-B-, -B-O-C- and -C-N-H- bonds are not studied enough. IR spectroscopy showed that these groups are a part of the PEDA luacromolecule composition. 

Detailed investigations are being conducted in the field of boron-nitrogen polymers with N— B coordinative bonds due to their hydrolytic stability (superior to that of the polymers containing tricoordinate boron). Such plastics and elastomers are likely to become candidates for special applications because of the high cross-section of 10B for the (n, a) reaction.171... 

A cautionary note is that, in addition to the polymer itself, the polymer additive system may contain elements other than carbon, hydrogen and oxygen. The detection of an element such as nitrogen, sulphur, halogens, phosphorus, silicon or boron in a polymer... 

As a typical example, isophthalonitrile was reacted with rert-butylborane-trimethylamine in diglyme at 100°C under nitrogen to produce a boron-containing polymer as shown in Scheme 4 (27). The white solid polymer was soluble in various organic solvents such as THF, chloroform and benzene. This polymerization involves the dimerization of iminoborane to form the four-membered ring as a key essential step. In this... 

For the preparation of poly(cyclodiborazane)s, a condensation method can also be used. For example, lV,JV -bis(trimethyl-silyl)terephthalaldehyde diimine was reacted with monochloro-dihexylborane to produce a boron-containing polymer with boron-nitrogen four-membered rings (31). This polymerization can be applied to various bis(silylimine)s such as N,N -bis(trimethylsilyl)isophthalaldehyde diimine. However, N,N -bis(trimethylsilyl)anthraquinone diimine gave only the monomeric iminoborane species and no polymer. 

Ceramic-type materials that contain no organic linkage units can be prepared by the pyrolysis of cyclic or high polymeric aminophosphazenes. An example is shown in reaction (44). Under appropriate conditions, pyrolysis products that correspond to phosphorus-nitride are formed. Polyphosphazenes that contain both amino and borazine side groups yield phosphorus-nitrogen-boron ceramics following pyrolysis 94,95 The conversion of a formable polymer into a ceramic has many potential advantages for the controlled synthesis and fabrication of advanced ceramics. This principle is discussed in more detail in Chapter 9. 

In the following sections some examples are given of the ways in which these principles have been utilized. The first example is the use of these techniques for the low temperature preparation of oxide ceramics such as silica. This process can also be used to produce alumina, titanium oxide, or other metal oxides. The second example describes the conversion of organic polymers to carbon fiber, a process that was probably the inspiration for the later development of routes to a range of non-oxide ceramics. Following this are brief reviews of processes that lead to the formation of silicon carbide, silicon nitride, boron nitride, and aluminum nitride, plus an introduction to the synthesis of other ceramics such as phosphorus nitride, nitrogen-phosphorus-boron materials, and an example of a transition metal-containing ceramic material. 

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