Comparison of the properties of polyimides derived from various dianhydride and diamine monomers

Dianhydrides 4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA) and dicyclo-hexyl-3,4,3',4'-tetracarboxylic dianhydride (HBPDA) were reacted with four different diamines to synthesize eight polyimide (PI) films through various heat treatment processes. BPADA contains aromatic benzene, whereas HBPDA contains alicyclic cyclohexane. The four diamine monomers contained either a linear benzene, highly electronegative trifluoromethyl (-CF₃) group, bulky sulfone (-SO₂-) group, or methyl (-CH₃) group between the benzene rings. The PIs obtained using the four different diamines and BPADA dianhydride were designated as series (I), while the PIs synthesized using HBPDA dianhydride were designated as series (II). To improve the physical properties of the synthesized PI films, all diamine structures contained hydroxy (-OH) groups capable of forming hydrogen bonds. The thermomechanical properties, optical transparencies, and solubilities of eight PI films synthesized from various monomer structures were investigated. Structure-property relationships were established through comparative analysis and film properties is also explained, and the results are compared. Overall, series (I), which contained aromatic dianhydride monomers, exhibited better thermomechanical properties than series (II) films, which contained cycloaliphatic dianhydride monomers. However, the optical transparency and solubility of the series (II) PIs were superior to those of the series (I) PI films.