A strategy for preparing spirobichroman dianhydride from bisphenol A and its resulting polyimide with low dielectric characteristic
A spirobichroman dianhydride (SBCDA) was prepared through oxidation of an octamethyl spirobichroman (OMSBC), which was synthesized from acid-fragmentation of bisphenol A by 3,4-dimethylphenol, followed by Diels–Alder reaction. The reaction mechanism was proposed, and the optimal reaction conditions were discussed. Based on a high temperature solution polymerization of SBCDA and 4,4′-diaminodiphenylmethane (DDM), a spirobichroman-containing polyimide, SBC-DDM, was successfully prepared. Because of the contorted spiro-structure and rigid polymer backbone, SBC-DDM exhibits a large free volume, leading to outstanding organo-solubility and a low dielectric constant. In addition, the resulting film of SBC-DDM shows foldability, a high glass transition temperature, and good thermal stability.