Synthesis and characterization of soluble poly(ether imide)s based on 2,2′-bis(4-aminophenoxy)-9,9′-spirobifluorene

A series of aromatic poly(ether imide)s containing 9,9′-spirobifluorene moieties in the main chain have been synthesized via the polycondensation of 2,2′-bis(4-aminophenoxy)-9,9′-spirobifluorene with a variety of aromatic dianhydrides. In the diamine monomer, the two aminophenoxyfluorene entities are orthogonally arranged and are connected through an sp3 carbon atom (the spiro center). The resulting poly(ether imide)s have a polymer backbone which is periodically twisted with an angle of 90° at each spiro center. This structural feature, which restricts the close packing of the polymer chains and reduces inter-chain interactions, leads to amorphous poly(ether imide)s with good solubility in common organic solvents. In addition, the rigidity of the main chain of these polymers appears to be preserved due to the spiro-structure. As a result, these poly(ether imide)s exhibit a high Tg and excellent thermal stability.