Heteroatom-doping or peripheral addition of functional groups are the major strategies used to enrich the chemical and physical properties of the polyphenylene-based frameworks. In this work, we describe the synthesis of the first BN-doped polyphenylenic material obtained through a decarbonylative [4 + 2] Diels-Alder cyclo-addition reaction between a tri-ethynylborazine unit and a bis-cyclopentadienone derivative. The BN-polymer was extensively characterized by FT-IR, solid-state C- and B-NMR and by comparison with the isolated monomeric unit. Given the unique thermal and chemical properties, the material was studied as potential support for solid state electrolytes, thus presenting great potential for the application of this new class of materials in lithium-ion batteries.