Effect ofDAPBOsegment on the structure and performance enhancement of powder foamedBTDA‐ODApolyimide

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Abstract
Achieving excellent thermal stability, good mechanical strength, and low‐density in one product, is a big challenge in the design and synthesis of polyimide (PI) foams. We selected a rigid diamine monomer, 2‐(4‐aminophenyl)‐5‐aminobenzoxazole (DAPBO) to partially replace 4,4′‐oxydianiline (ODA) in BTDA‐ODA system, and studied the effect on properties of foamed PI products. With various molar ratio between DABPO and ODA (0:5, 1:4, 2:3, 3:2, 4:1, 5:0), the diamine(s) polymerized with 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA) and produced six PI precursors (PAE‐0 ~ PAE‐5). After foaming and thermal imidization, corresponding PI foams (PI‐0 ~ PI‐5) prepared. Among them, PI‐3 has a glass transition temperature of 386°C, which is 95°C higher than PI‐0, and its compressive strength reaches 1.32 MPa. Moreover, PI‐3 has a uniform cell structure with an average pore size of ~200 μm. The analysis results show that PI‐3 is in a transition state from amorphous to partial crystalline, maintaining a balance between flexibility and rigidity. The addition of DABPO not only increases the rigidity of polymer molecular segments, but also introduces N and O atoms that can form intermolecular hydrogen bonds between molecules, which increases the packing density and arrangement regularity of polymer molecules.

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