Preimidization of Unreactive Cycloaliphatic Dianhydrides to Enable Room-Temperature Polymerization for Colorless Polyimides

Cycloaliphatic monomers can produce low-color polyimides, but their low reactivity makes it difficult to create high-quality free-standing films. This study addressed this by preimidizing low-reactivity cycloaliphatic dianhydrides with excess standard diamine, yielding imide-containing diamines suitable for room-temperature polymerization with a second dianhydride. The resulting high molecular weight copolymers exhibited excellent solubility and processability and could be further imidized to form quality polyimide films. These films were systematically evaluated for their optical, thermomechanical, and mechanical properties. Additionally, a method involving in situ preimidization and chain extension for film fabrication was demonstrated.