Synthesis and characterization of branched phenylethynyl-terminated polyimides

A series of PEPA-TAP-ODA-6FDA branched phenylethynyl-terminated polyimides (BPIs) are successfully synthesized by incorporation of branching units into the linear PI. The molecular structures, thermal and rheological properties of the BPIs are investigated and characterized by FTIR, ¹H NMR, elemental analysis, TGA and rheological test. All the BPIs exhibit high transparent in visible region, high solubility, excellent thermal stabilities and melting processability. All the BPIs have excellent thermal stabilities, and the corresponding T₅ and heat resistance index values of the BPIs are all higher than 470 and 265 °C, respectively. All the BPIs have a relatively lower melt viscosity values. Compared to that of neat PI, the minimum melt viscosity values of the BPIs are all decreased obviously. Herein, BPIs-b exhibits the minimum melt viscosity (210 Pa•s), far below than that of neat PI (1260 Pa•s).