Polyimide structure–property relationships. III. Polyimides from multi‐ring diamines

Abstract

The effects of increasing the distance between, and varying the isomeric positions of, the amine groups on the glass transition temperatures of aromatic polyimides were studied in order to investigate routes to improve processability. A number of isomers of three‐ and four‐ring benzenoid diamine systems were polymerized with 3,3′,4,4′‐benzophenone tetracarboxylic acid dianhydride to poly(amic acids), which were converted to polyimides. The use of methylene and carbonyl groups to connect the benzene rings of the diamines, and in one case the dianhydride, afforded a comparison of the thermomechanical properties of the polyimides to those prepared from diphenylmethane‐ and benzophenone‐diamines, respectively. Generally, the dilution of the imide content by the insertion of benzylene and benzoylene segments into the diamines significantly reduced the glass transition temperatures, with the benzylene group being more effective in that respect than the benzoylene. However, there was evidence that the position isomerism (ortho, meta, para) of the amine groups was more influential in affecting the glass transition temperatures of aromatic polyimides than was the dilution of the imide content.