Comparison of properties of colorless and transparent polyimide films using various diamine monomers

Abstract Six different types of polyamic acids were synthesized by reacting 1,2,4,5-cyclohexanetetracarboxylic dianhydride with the diamine monomers 3,4-oxydianiline, 1,3-bis(3-aminopheno- xy )benzene, 1,4-bis(4-amino-phenoxy)benzene, m -bis[4-(3-aminophenoxy)phenyl]sulfone, p -bis[4-(4-aminophenoxy)-phenyl]sulfone, and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane. Thereafter, polyimide (PI) films were prepared via various heat treatment processes. The diamine monomers used in this study for the synthesis of colorless and transparent PI (CPI) were characterized by a bent meta-structure or a para-linear chain containing ether (–O–) bonds. In addition, some monomers included fluorine (–CF 3 ) substituents and sulfone (–SO 2 –) groups. Furthermore, the thermal and mechanical properties, optical transparency, and solubility of the CPI films with six different diamine monomer structures were investigated. The correlation between CPI film properties and related monomer structures was specifically emphasized.