Lightweight polyimide foams (PIFs) with exceptional thermal resistance and compressive properties are fabricated by heating polyester ammonium salts (PEASs) which are prepared by copolymerizing 4, 4'-diaminobenzanilide (DABA), 4, 4'-diaminodiphenyl methane (MDA) and 3, 3', 4, 4'-benzophenone tetracarboxylic dianhydride (BTDA). Hydrogen bonds are formed between CONH and CO in the PI chains due to the addition of DABA and the melt viscosity of PEAS precursors increase with increasing content of DABA, which is advantageous to bind the foaming gases for cell expansion. The expansion ratio of PEAS precursors is increased from 633% to 1133% when the molar ratio of MDA/DABA is changed from 10:0 to 6:4. The compressive strength and modulus of PIFM9D1 (i.e., the molar ratio of MDA/DABA is 9:1, foam density: 120.8 kg m-3 ) reach as high as 0.59 and 15.0 MPa, respectively. The PIFs possess prominent thermal performance with the initial thermal degradation temperatures (under both nitrogen and air atmosphere) and glass transition temperatures (as assessed by DSC and DMA) exceeding 511 and 292 °C, respectively. The thermal conductivity of PIFs is lower than 0.049 W m-1 K-1 , which exhibits promising applications for serving as high-temperature thermal insulation materials in the fields of aerospace, marine, and nuclear sectors among others.
Keywords: copolymerization; hydrogen bonding; mechanical properties; polyimide foams; thermal properties.
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