Combining Microwave‐Assisted Foaming and Post Curing Process to Prepare Lightweight Flexible Polyimide Foams for Thermal Insulation Applications

Abstract

Lightweight flexible polyimide foams (PIFs) with different rigid‐flexible molecular structure networks are prepared by microwave‐assisted foaming of polyester ammonium salt (PEAS) precursor powders, followed by post curing process to complete final imidization. The optimum foaming temperatures of PEAS precursors range from 85 to 135 °C, and the melting rate of PEAS is adjusted to meet the volatile releasing rate to fabricate PIFs. Results show that PIFs with nearly fully open cell rate (99.99%), micron pore sizes (400–500 µm), and micro/nano multiscale structures exhibit excellent mechanical flexibility and elasticity. The prepared PIFs demonstrate exceptional thermal stability and heat resistance in both dynamic and static environments. The PIFs possess low thermal conductivity and superior thermal insulation properties that demonstrate potential applications in high‐tech fields such as aerospace, marine use, and microelectronics among others.

Lightweight, Radiation-Resistant, and Flexible Polyimide Foams with an Anisotropic Porous Structure for Efficient Thermal Insulation Applications

“…In contrast, although PIF BTDA/MDA–DMBZ possessed the most rigid molecular chain, the mechanical properties were reduced due to its largest foam pore size (395 μm). In summary, the PIFs possessed excellent compressive properties (compressive strength at 10% strain: 68.67–95.45 kPa) and high elasticity (compression response rate at 50% strain: 96–98%), which were superior to those of the previously reported flexible PI porous materials, ,,− as tabulated in Table S3.…”

“…Thermal conductivity of PIFs in the (a) vertical direction and (b) horizontal direction. (c) Comparison of thermal conductivity between the PIFs and other porous materials, including ANF/PI aerogel (ref ), MXene/PI aerogel (ref ), PI/aramid sponge (ref ), PI foam (ref ), PI/red phosphorus/graphene foam (ref ), PI foam (ref ), CNTs@CoFe 2 O 4 /PI aerogel (ref ), HAnws/PI aerogel (ref ), SiO 2 /PI aerogel (ref ), PI/bacterial cellulose aerogel (ref ), and PI foam (ref ). (d) Top surface temperatures of PIFs [(d 1 ) PIF BTDA/ODA–MDA , (d 2 ) PIF BTDA/ODA–DMBZ , (d 3 ) PIF BTDA/MDA–DMBZ , (d 4 ) PIF BTDA/ODA&BTDA/MDA , (d 5 ) PIF BTDA/ODA&BTDA/DMBZ , and (d 6 ) PIF BTDA/MDA&BTDA/DMBZ ].…”

Fabrication of Lightweight Polyimide Foams with Exceptional Mechanical and Thermal Properties

“…The compressive curves are divided into three distinct regions: 1) the initial linear elastic region, corresponding to the bending of the edges of elastic foam cells; 2) the stress plateau region which is related to the elastic yielding and bending of foam cells; 3) the stress‐dense region which is related to the densification of bubble walls. [ 47 ] It should be noted that the stress corresponding to 10% strain was considered as the compressive strength, and the compressive modulus was obtained as the slope of strain ≤3%. Three specimens were tested for each sample.…”

Applications of flexible polyimide: barrier material, sensor material, and functional material

“…The material parameters comprise a range of elements such as monomer type, cross-linking agent type, monomer mole fraction, number of main chain repeat units, and polymer concentration. To begin with, the type of monomer (diamine and dianhydride) is a critical aspect in the synthesis of PI, and the functional group, stiffness, and intrinsic qualities of PI will influence the chain's interaction, shrinking, form, and performance [67] . Ni et al obtained the precursor powder of polyester ammonium salt (PEAS) by the polymerization reaction with three different diamine monomers (4,4′-diaminodiphenyl ether (ODA), 4,4′-diaminodiphenylmethane (MDA), 4,4′-diamino-2,2′dimethylbiphenyl (DMBZ)) and 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BTDA) [68] .…”