The polychaete worms of the Nereididae family are distinguished by lightweight, conical teeth that exhibit a hardness level analogous to human dentin. While comparable in material properties to the mineral comprising dentin, the polychaete worm’s teeth are proteinaceous material built from histidine rich proteins cross-linked with Zn+2 ions through coordination chemistry. The exemplified material properties achieved through coordination cross-linking of such biomaterials has inspired us to extend this method of cross-linking to preceramic polymers. Preceramic polymers require rigorous cross-linking as a means to reduce volume shrinkage and mass loss during pyrolysis, and often require extensive thermal curing steps to prepare a green body viable for ceramitization. Coordination cross-linking offers a faster, dynamic platform to preparing preceramic green bodies. Herein, we report the functionalization of commercially available polysiloxane and polycarbosilane backbones with pyridyl-moieties and the subsequent coordination cross-linking of these polymers with Zn+2 and Ti+4 ions. The rapidly cross-linked materials were characterized with ATR-FTIR, oscillatory rheology, and thermal gravimetric analysis. The cross-linked green bodies were then pyrolyzed at 1400°C to ceramic materials, and characterized with XPS, XRD, and TEM. Ceramics generated from coordination cross-linked preceramic polymers represent the metal ion cross-linker, with Ti+4 cross-linked polymers generating TiC/SiC, and Zn+2 cross-linked materials generating SiC, as Zn+2 evaporates between 1000–1200°C. Coordination cross-linking is a single dial that can adjust material characteristics before and after pyrolysis. Particularly, the viscoelastic properties, thermal stability, and ceramic yields at 800°C can be systematically changed with the loading equivalents of metal cross-linker and the ceramic composition can be changed by metal ion choice. To the best of our knowledge, this is the first example of silicon-based preceramic polymers cross-linked through pyridine-based metal ion coordination.

Bioinspired cross-linking of preceramic polymers via metal ion coordination bonding

ACS Spring Meeting 2021

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