No abstract

Rigid polymer networks with aromatic polyimide (PI) backbones end‐linked with symmetric crosslinkers are designed. 1,3,5‐Tris(4‐aminophenyl)benzene (TAPB) and tetra(4‐aminophenyl)methane (TAPM) are used as the crosslinkers. Whereas TAPB has three reactive amines at planar threefold symmetric (C3) positions, TAPM has four amines at tetragonal (S4) positions. Poly(amide acid) (PAA) precursors are end‐linked with TAPB or TAPM to make PAA networks. The crosslinking reaction efficiencies and mechanical properties of the PAA gels are investigated by the sol fraction method and compressive stress–strain tests, respectively. The PAA gels are successively transformed to PI gels through chemical imidization treatments. From the swelling behavior, it is found that the PI gels have high void contents up to 70%.

Front Cover: The framework structure of rigid poly(amide acid) and polyimide networks can be tuned by the selection of a robust and symmetric crosslinker structure. The S4‐symmetric four‐armed crosslinker can provide homogeneous network structures compared with the C3‐symmetric three‐armed crosslinker. Further details can be found in the article by N. Yoshihara, N. Hosono,* R. Ohshima, K. Totani, and T. Watanabe* on page 988.