Materials that can dissipate, reflect or absorb heat, are electrically insulating, have high-tensile strength, and are stable at high temperatures are crucial for many high-performance applications. Such materials find use in transport (heat resistance, friction, extreme loads); aerospace and space systems (robust wave transparent materials); electronics (non-conductive, heat dissipating materials); and functional woven textiles (thermal management). One example, of many, in the use of these so-called "next generation materials" comes from their potential for deployment in aeronautics or space technologies (hypersonic aircraft), where electrically insulating materials are required for high-voltage applications that can withstand atmospheric re-entry conditions and extreme levels of radiation. Such materials must also be easily processable, of relatively low cost, and amenable to efficient and scalable manufacture, especially of continuous fibres that allow for the shaping of the complex forms necessary for specific applications.
Hexagonal boron nitride (h-BN) is one such material. A close cousin of graphite/graphene (having a very similar structure where "BN" replaces "CC"), h-BN has excellent heat conductivities, is an electrical insulator, is chemically very stable (to over 1000 C in air), and is considered non-hazardous. However, current routes to continuous h-BN fibres are very expensive, use difficult to obtain precursors and have not been demonstrated on a commercial scale. This is in contrast to societally and technologically ubiquitous carbon fibres, that are produced on a huge scale (120kton/pa) from polymer precursors such as polyacrylonitrile. Equivalent h-BN fibres would possess all the benefits of carbon fibre (low weight/thermal expansion and high tensile-strength/shock resistance) but also have desirable thermal management, electronic (insulating) and chemical stability benefits that carbon fibre does not. In many respects, h-BN is the perfect next generation material. What is needed to overcome current roadblocks in h-BN fibre production is a relatively simple, cost-effective, and scalable source of polymer pre-ceramic, that can then be processed in a continuous and efficient manner to form h-BN fibres. We propose that a relatively new type of BN-containing polymer, polyaminoboranes (PAB), could be such ideal precursors. While PABs are made by atom-efficient catalytic coupling of smaller, accessible, precursor amine-borane units, e.g. H3B.NMeH2, they have not been used as fibre precursors due to the historical lack of reliable, scalable and controlled routes for their synthesis.
This proposal directly addresses this technological gap by bringing together expertise in two complementary fields: organometallic catalysis and mechanism for the controlled and efficient synthesis of PAB on scale (Weller), and the manufacture of high-performance nanomaterials using continuous fabrication methods (Grobert). Recent breakthroughs by Weller (scalable PAB synthesis) and Grobert (proof of principle PAB-fibre production) now show that PAB are perfectly poised to be processable preceramics to h-BN fibres. Encouraged by these exciting joint preliminary results we will develop scalable routes to high-quality h-BN fibres. This will be done through developing straightforward, controlled and efficient routes to the precursor polyaminoboranes, for which mechanism-led design strategies will be used to optimise catalytic control over the polymer characteristics. The production of bespoke B-N main chain polyaminoborane systems on scale will fully unlock their use as precursors for the fabrication of ultra-light-weight, mechanically strong, continuous h-BN ceramic fibres. The translation of our scientific breakthroughs into a broader industrial context will be enabled through close engagement with our industry project partners Boron Specialties, Strathclyde Light Weight Manufacturing Centre & Williams Advanced Engineering.
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