Mechanically Strong, Thermally Stable, and Flame Retardant Poly(ether imide) Terminated with Phosphonium Bromide

Abstract

High mechanical strength, thermal stability, and flame retardancy are three crucial criteria for highperformance polymers to be suitable for aerospace applications. Most polymers, however, cannot meet the three criteria simultaneously. Herein, phosphonium bromide-terminated poly(ether imide)s (PEI-PhPPh 3 Br) simultaneously possessing high mechanical strength, thermal stability, and flame retardancy were synthesized by functionalizing dianhydrideterminated poly(ether imide)s (PEI-DA) with triphenyl-4aminophenylphosphonium bromide. With the judiciously designed end group, PEI-PhPPh 3 Br exhibited excellent tensile properties, thermal stability, and flame retardancy. Importantly, PEI-PhPPh 3 Br with a molecular weight of 12 kDa [PEI-PhPPh 3 Br (12k)] showed a tensile strength of 109 ± 4 MPa and a Young's modulus of 2.75 ± 0.12 GPa, much higher than those of the noncharged PEI analogue. Additionally, PEI-PhPPh 3 Br (12k) showed outstanding flame retardancy, better than the state-of-the-art commercial PEIs, as evidenced by the high limiting oxygen index of 51% and high char yield of 60% at 980 °C. The study herein provides a highly effective strategy to simultaneously improve mechanical strength, thermal stability, and flame retardancy, which are three important properties rarely possessed by most polymers.

Recent development of polyimides: Synthesis, processing, and application in gas separation

“…As previously mentioned, end-groups such as ureidopyrimidinone, 21 sulfonate salts, 22,23 and phosphonium salt 24,25 endow oligomers with outstanding thermal and mechanical properties, making them comparable to even benchmark PEIs. However, the solvent resistance remains similar to the pristine PEIs because these linkages are noncovalent.…”

“…Based on this concept, low-molecular-weight PEI oligomers have recently been enhanced by hydrogen bonding 21 and ionic forces. [22][23][24][25]…”

“…After processing, the oligomers can be linked together via molecular interactions to enhance chain entanglement and compensate for thermal/mechanical performance loss. Based on this concept, low‐molecular‐weight PEI oligomers have recently been enhanced by hydrogen bonding 21 and ionic forces 22–25 …”

“…To this point, two methods are presented for improving processibility, including polymer blending and oligomers engineering. [21][22][23][24][25] In light of the energy crisis and to advocate the goal of sustainable development by United Nations, 26 we dedicate a section that focuses on gas separation using HPPs, because efficient gas separation technology could immensely reduce human energy consumption and help lessen humanities global carbon footprint. With the goal of guiding further development, some critical challenges to the advancement of HPP technology are highlighted and discussed.…”

“…Even though well‐established, these HPPs still face challenges, like low processibility that increases production costs. To this point, two methods are presented for improving processibility, including polymer blending and oligomers engineering 21–25 . In light of the energy crisis and to advocate the goal of sustainable development by United Nations, 26 we dedicate a section that focuses on gas separation using HPPs, because efficient gas separation technology could immensely reduce human energy consumption and help lessen humanities global carbon footprint.…”