Design of a Series of PreceramicB-Tri(methylamino)borazine-Based Polymers as Fiber Precursors: Architecture, Thermal Behavior, and Melt-Spinnability†

Straightforward Design Strategy toward 3D Near-Net-Shape Stoichiometric SiC Parts

Fused deposition modeling (FDM), traditionally reserved for thermoplastics, is modified here with a granule-based extrusion head to be extended to advanced nonoxide ceramics via a straightforward design strategy that considers the shaping opportunities and the chemical richness offered by preceramic polymers. Specifically, 3D near-net-shape stoichiometric silicon carbide (SiC) objects are designed by manipulating the key features of a commercially available polycarbosilane (fusibility, high carbon content, relatively high SiC yield). In the early stage of the process, the carbon-rich polycarbosilane is first mixed with Si and SiC fillers and then thermolyzed at 120 °C to increase polymer branching while offering tailored rheological properties during the subsequent extrusion process at 90 °C and adequate shape retention once extruded. This allows for the design of tailored and complex 3D complex polycarbosilane-based architectures with features down to 400 µm. Polymer-based parts are further converted into 3D stoichiometric SiC objects with quasi-near-net-shape-a volume shrinkage reduced to 9.1% is measured-by heat treatment at a temperature as low as 1400 °C (argon flow). Given the flexibility to tune the preceramic polymer chemical and rheological properties, a new combined design approach is leveraged to generate bespoke advanced ceramics with a high freedom in geometry complexity.

Approaches to Preceramic Polymer Fiber Fabrication and On-Demand Applications

The demand for lightweight, high-modulus, and temperature-resistant materials for aerospace and other high-temperature applications has contributed to the development of ceramic fibers that exhibit most of the favorable properties of monolithic ceramics. This review demonstrates preceramic-based polymer fiber spinning and fiber classifications. We discuss different types of fiber spinning and the advantages of each. Tuning the preceramic polymer chemical properties, molar mass, functional chemistry influences, and incorporation with fillers are thoroughly investigated. Further, we present the applications of preceramic-based polymer fibers in different fields including aerospace, biomedical, and sensor applications. This concise review summarizes recent developments in preceramic fiber chemistry and essential applications.

Boron nitride ceramics from molecular precursors: synthesis, properties and applications

Hexagonal boron nitride (h-BN) attracts considerable interest particularly when it is prepared from borazine-based single-source precursors through chemical routes suitable for the shaping and the nanostructuration of the final ceramic.

Polymer-Derived Boron Nitride: A Review on the Chemistry, Shaping and Ceramic Conversion of Borazine Derivatives

Boron nitride (BN) is a III-V compound which is the focus of important research since its discovery in the early 19th century. BN is electronic to carbon and thus, in the same way that carbon exists as graphite, BN exists in the hexagonal phase. The latter offers an unusual combination of properties that cannot be found in any other ceramics. However, these properties closely depend on the synthesis processes. This review states the recent developments in the preparation of BN through the chemistry, shaping and ceramic conversion of borazine derivatives. This concept denoted as Polymer-Derived Ceramics (PDCs) route allows tailoring the chemistry of precursors to elaborate complex BN shapes which cannot be obtained by conventional process. The effect of the chemistry of the molecular precursors, i.e., borazine and trichloroborazine, and their polymeric derivatives i.e., polyborazylene and poly[tri(methylamino)borazine], in which the specific functional groups and structural motifs determine the shaping potential by conventional liquid-phase process and plastic-forming techniques is discussed. Nanotubes, nano-fibers, coatings, monoliths and fiber-reinforced matrix composites are especially described. This leads to materials which are of significant engineering interest.

Ordered mesoporous polymer-derived ceramics and their processing into hierarchically porous boron nitride and silicoboron carbonitride monoliths

This review describes the elaboration of ordered mesoporous non-oxide materials such as BN and SiBCN and the subsequent fabrication of derived monoliths by spark plasma sintering using the as-prepared powders.

Polymerization of N-methyl B-methyl amino borazine

A large quantity of high-quality poly[N-methyl B-methyl amino borazine] was synthesized via a solventless method from the monomer 1,3,5-trimethyl-2,4,6-tri(methyl amino)borazine. The thermal polymerization profile was investigated with differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), size exclusion chromatography (SEC), gas chromatography, and mass spectrometry. A polymerization mechanism involving the condensation reaction of two –N(H)CH3 groups releasing methylamine was proposed and compared with the literature. As a result of cross-linking via the amino­methyl moiety, the cured polymer exhibited a molecular weight Mn of 790 g mol-1, glass transition temperature of 64°C, high cross-link density, and thermal stability with a decomposition temperature of 165°C. Functionalized poly[N-methyl B-methyl amino borazine] with chemical stability was fully characterized by 1H, 13C, 11B nuclear magnetic resonance, FTIR, DSC, and SEC analyses. Ultraviolet absorption spectra evidenced changes in the structure of the aforementioned oligomers.

A new class of boron nitride fibers with tunable properties by combining an electrospinning process and the polymer-derived ceramics route

Novel boron nitride (BN) fibers have been developed with diameters ranging from the nano- to microscale by thermal conversion of as-electrospun fibers from polyacrylonitrile and poly[B-(methylamino)borazine] blend solutions. Such a new class of ceramic fibers is seen as potential candidate for thermal management applications and filtration systems in harsh environments.