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

Abstract

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.

New High-Performance Materials: Bio-Based, Eco-Friendly Polyimides

“…The imidization degree attained by microwaves was double the size of the one obtained by common thermal cyclization at 200°C and was almost complete at 250°C. Moreover, the PIs obtained by microwaves displayed higher thermal stability and superior mechanical resilience (even up to 30% higher) as compared to their thermally imidized counterparts [115,117,127].…”

“…The outstanding downsizing of reaction time is the strongest point of this experimental technique. Microwave-assisted polycondensation reactions proceed very rapidly, requiring only a few minutes of irradiation to obtain binary or ternary soluble polyimides with more than acceptable inherent viscosity (up to 1.2 dL/g) and molecular masses (up to 200 kDa) [117]. The irradiation time is a key parameter that can easily turn from a benefit to a drawback.…”