A synthetic route is described to a new monomer, N-(2-biphenylenyl)-4-[2'-phenylethynyl]phthalimide (BPP), which contains both phenylethynyl and biphenylene reactive functional groups. The monomer can be made either from N-(2-biphenylene)acetamide or 2-amino-biphenylene, by reaction with the phenylethynyl-containing anhydride. The monomer was characterised fully and the thermal cure of the material was studied by infrared (IR) spectroscopy and differential scanning calorimetry (DSC). The IR spectra showed that the phenylethynyl group reacted completely within 1 h at 370 degreesC. DSC showed the polymerisation exotherm of BPP centred at 379 degreesC, lower than two NASA-developed phenylethynyl-terminated imide (PETI) resins. In comparison with the PETI systems, the T-g of cured BPP was ca. 100 degreesC higher, making it a candidate for possible high temperature applications.