Advances in the Synthesis of Preceramic Polymers for the Formation of Silicon-Based and Ultrahigh-Temperature Non-Oxide Ceramics

Abstract

Preceramic polymers (PCPs) are a group of specialty macromolecules that serve as precursors for generating inorganics, including ceramic carbides, nitrides, and borides. PCPs represent interesting synthetic challenges for chemists due to the elements incorporated into their structure. This group of polymers is also of interest to engineers as PCPs enable the processing of polymer-derived ceramic products including high-performance ceramic fibers and composites. These finished ceramic materials are of growing significance for applications that experience extreme operating environments (e.g., aerospace propulsion and high-speed atmospheric flight). This Review provides an overview of advances in the synthesis and postpolymerization modification of macromolecules forming nonoxide ceramics. These PCPs include polycarbosilanes, polysilanes, polysilazanes, and precursors for ultrahigh-temperature ceramics. Following our review of PCP synthetic chemistry, we provide examples of the application and processing of these polymers, including their use in fiber spinning, composite fabrication, and additive manufacturing. The principal objective of this Review is to provide a resource that bridges the disciplines of synthetic chemistry and ceramic engineering while providing both insights and inspiration for future collaborative work that will ultimately drive the PCP field forward.

Efficient Cobalt-Catalyzed Coupling of Amines and Siloxanes to Prepare Ceramics and Polymers

“…Silicon nitride (Si 3 N 4 ) and silicon oxynitride (SiO x N y ) materials and coatings offer exceptional structural stability at temperatures of up to 1400 °C. , Raw Si 3 N 4 powder is produced following the reaction of N 2 with Si and textured using hot-press and sintering techniques. − Chemical vapor deposition using SiCl 4 /NH 3 , SiH 4 /NH 3 , or aminosilane monomers offers a route to Si 3 N 4 coatings. − The pyrolysis of preceramic polymers is a third methodology that generates Si 3 N 4 and SiO x N y ceramics. − Polysilazanes, which feature a repeating backbone of Si–N bonds, have been used as preceramic polymers for more than four decades to coat semiconductors and building materials. , However, they are largely accessed through the ammonolysis or aminolysis of halosilanes (Figure a) . The corrosive nature of halosilanes and generation of an equivalent of ammonium salt waste for each Si–N bond that is formed are major drawbacks of this approach.…”

Nanolayered Ceramic-Confined Graphene Aerogel with Conformal Heterointerfaces for Low-Frequency Microwave Absorption

“…Polymer-derived ceramics (PDCs), as a representative class of multiphase materials with a coexisting crystalline and amorphous structure, exhibit multiple heterogeneous interfaces and thermal and chemical stability. In addition, the crystalline domain structure within PDCs can be tailored via the manipulation of the heat treatment process, resulting in an enhanced EMW absorption performance. , …”

“…In addition, the crystalline domain structure within PDCs can be tailored via the manipulation of the heat treatment process, resulting in an enhanced EMW absorption performance. 23,24 In this study, to maximize the advantages of heterostructures, an effective method that involves coating graphene aerogels with a conformal dielectric polymer-derived silicon carbonitride (SiCN) nanoceramic via precursor infiltration and pyrolysis was presented to generate conformal heterointerfaces between graphene and SiCN. The resulting 2D sandwiched SiCN/graphene/SiCN cell wall with a double-level impedance gradient ameliorates the surface impedance matching between the graphene and air, thus enabling incident EMWs to enter the interior of the ceramic-confined graphene aerogel (GA/C).…”

Palladium-Catalyzed Cross-Coupling Polymerization of Bis-N-tosylhydrazones and Bis(silyl) Aryls: A New Access to Polycarbosilane Synthesis

“…The development of novel polymerization methods and related processes is of great importance in enriching the diversity of polymer science and accessing various functional materials. − As one of the most important families of functional materials, organosilicon polymers have been widely applied in adhesives, coatings, ceramics, moldings, and sealing materials. − In particular, polycarbosilanes containing Si–C bonds in polymer backbones have received extensive investigation due to their low toxicity, high chain flexibility, and excellent thermal and oxidative resistance. ,− The catalytic synthesis of polycarbosilanes traditionally relies on the hydrosilylation polymerization of alkenes and silanes, typically by Pt-based catalysts such as Speier’s and Karstedt’s catalysts. − More recently, rare earth metal catalysis, early transition-metal catalysis, , borane-based catalysis, , and photocatalysis , have emerged as new tools (Scheme a). In contrast to widely investigated hydrosilylation polymerization of alkenes, in which regioselectivity issues should be taken into consideration, other strategies are much less exploited and developed …”