Blend of polyimide having internal acetylene units and oligoimide end-capped with biphenylenes

A N-Methylpyrrolidone (NMP) solution of polymic acid having internal acetylene units in the backbone was mixed with a NMP solution of oligomeric amic acid end-capped with biphenylenes to afford a miscible solution. The viscosity of polymic acid solution lowered considerably by the addition of oligomers, which could lead to improved processability. The amic acid mixture was thermally or chemically cyclized to give a blend of internal-reactive polymide and end-reactive oligoimide. Films of imide blends were easily prepared by casting solutions of the amic acid blends followed by imidization. The imide blends were thermally cured at 400°C for 10 min to give cross-linked polyimides that showed excellent thermal stability as confirmed by DSC, TGA, TMA, and viscoelastic analyses of the cured films. A selective co-crosslinking reaction between biphenylene in the oligomide and acetylene in the polyimide to give phenanthrene linkage is supposed to be the cause of the high thermal stability.