The Influence of Residual Copper Catalyst on the Polymer-to-Ceramic Conversion of a Click-Derived Polycarbosilane

Authors

Abstract

Preceramic polymers (PCPs) are an emerging class of materials for the preparation of advanced ceramic components. Following conventional polymer processing and subsequent pyrolysis, polymer derived ceramic (PDC) fibers, monoliths, and composites offer novel engineering opportunities for aerospace applications. Despite the rapidly emerging commercial applications of PDCs, understanding the basic science governing structural transformation of the polymer to final ceramic and its eventual effect on materials properties is poorly understood. PCPs prepared using a mild and scalable copper (Cu) catalyzed azide/alkyne click reaction have been demonstrated as a unique class of material that can bind with transition metals, ultimately producing ultra-high temperature ceramics (UHTCs) upon pyrolysis. Unexpectedly, it was found that removal of residual Cu catalyst from a model click-derived polycarbosilane PCP significantly reduced the ceramic yield during pyrolysis. Herein we report the influence of Cu impurities on polycarbosilane-derived SiC ceramics and present a mechanistic understanding of the unintended role of Cu on the polymer-to-ceramic conversion process. Synchrotron-based scattering and spectroscopy methods were implemented to track the evolution of different atomic species and local structure and the influence of Cu toward atomic-scale structure in the final ceramics. It was determined that the Cu impurities catalyze the formation of silicon carbide through the formation of intermediate copper/copper silicide clusters, ultimately increasing the ceramic yield. Overall, this contribution highlights the need to carefully assess the interplay between the chemistries needed for PCP synthesis and their potential influence in final PDCs following ceramic processing.