Design of a Series of Preceramic B-Tri(methylamino)borazine-Based Polymers as Fiber Precursors: Architecture, Thermal Behavior, and Melt-Spinnability

A series of poly[ B -(methylamino)borazine] were synthesized by thermolysis of a monomeric B -tri(methylamino)borazine at various temperatures between 150 and 200 °C and then characterized for suitability as a fiber precursor. Polymerization mechanisms and polymer architectures are discussed. It was shown that poly[ B -(methylamino)borazine] represents a network combining a majority of −N(CH 3 )− bridges with a small proportion of B−N bonds, both connecting borazine rings, and −N(H)CH 3 groups. Both the ratio between flexible −N(CH 3 )− bridges and rigid B−N bonds and the relative amounts of plasticizing −N(H)CH 3 groups cause different responses to thermal properties and spinnability (glass transition, spinning temperatures, melt throughput, and fiber drawing). Based on fiber shape visualization using CCD camera during extrusion, appreciable melt-spinnable compounds are prepared between 160 and 185 °C. Such polymers display a chemical formula of [B 3.0 N 4.4 ± 0.1 C 2.0 ± 0.1 H 9.3 ± 0.2 ] n ( n ∼ 7.5), a glass transition between 64 and 83 °C, tailored flexibility, and sufficient plasticity to successfully produce fine-diameter green fibers.