Synthesis of Acetoxy Substituted Polyimide Copolymers for Improved Solubility in Organic Solvents

Polyimides (PIs) possess excellent thermal and mechanical properties, but their poor solubility in organic solvents restricts their utility. Numerous studies have focused on improving PI solubility by weakening inter-molecular interactions within the polymer. The polyimide composed of aromatic anhydride, 6,6′-(hexafluoroisopropylidene)dipthalic anhydride and aromatic diamine, 4,4′-oxidianiline, is known to be soluble, but solubility at room temperature is very limited. In this study, a soluble polyimide copolymer, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (Bis-ap-af), a diamine containing hydroxyl groups, was incorporated into the above-mentioned PI via chemical and thermal imidization. Chemical imidization resulted in the acetylation of the hydroxyl groups of Bis-ap-af units, while the hydroxyls remained intact under thermal imidization conditions. The acetoxy-containing soluble polyimide copolymers displayed improved solubility in a number of organic solvents compared to the conventional PI, and the copolymer films maintained their mechanical properties and presented reduced yellowness.