Molecular-scale understanding on the structure evolution from melamine diborate supramolecule to boron nitride fibers

Abstract The melamine diborate (C3N6H6·2H3BO3) supramolecules are very promising precursor to boron nitride (BN) fibers in addition to polyborazane. However, deep understanding on the structure evolution from C3N6H6·2H3BO3 into BN remains rare, thus limiting the precise regulations on the constituents of BN fibers and their performance improvement. Herein, we provided a molecular-scale insight into this evolution process. Specifically, dehydration of boric acid and condensation of melamine generated the boron oxide oligomer tangled with melamine condensates in first stage, then cross-linking of the two parts gave formation of the polymer network, afterwards decomposition of triazine ring promoted the nitridation of boron oxide to evolve into the BN structure, and the structure rearrangement facilitated crystallization in final. This transformation mechanism could be used to instruct the regulation on the constituents of BN fibers through controlling pyrolyzing reactions of C3N6H6·2H3BO3, and to further realize performance optimization.