Improved synthesis and properties of BTDA-TDI/MDI ternary copolyimides via microwave-assisted polycondensation

Polyimides are usually synthesized over a long period of time, and the process is complex. In order to shorten the synthesis time and simplify the process, we developed an improved synthesis method, namely, microwave-assisted polycondensation. The 3,3′-4,4′-benzophenone tetracarboxylic dianhydride (BTDA)–2,4-tolylene diisocyanate (TDI)/1,1′-methylenebis(4-isocyanatobenzene) (MDI) ternary copolyimides prepared in this work have been synthesized using microwave heating at rather short reaction times (15 min), without the need for either the once-off addition of TDI/MDI or the drop-wise addition of that mixture. The structure of the desired ternary copolyimide was confirmed by proton nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy. Its glass-transition temperature is above 400°C, and the temperature for 5% thermal loss under nitrogen atmosphere is 508.8°C. The tensile strength is 141 MPa, which shows that the microwave-assisted copolyimide has excellent heat resistance and mechanical properties.