Study of physicochemical properties of meta and ortho trifluoromethyl substituted isomeric aromatic polyimides

Two novel isomeric fluorinated diamines were synthesized via Williamson etherification reaction. Their polymerization was carried out with commercially available anhydrides i.e., 3,3′,4,4′-Benzophenone tetracarboxylic dianhydride (BTDA), pyromellitic dianhydride (PMDA), 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropanedianhydride (6FDA) and oxydipthalic anhydride (ODPA) respectively. A series of meta substituted fluorinated polyimides PD-11, PD-13, PD-14, PD-15 and ortho substituted fluorinated polyimides PD-41, PD-43, PD-44, and PD-45 were synthesized from each respective anhydride and diamine. FTIR confirmed the successful synthesis of polyimides with characteristic peaks. Solubility studies revealed comparable solubility attitude for meta and ortho substituted fluorinated polyimides, only PD-14 and PD-44 were soluble at room temperature. The other polyimides showed solubility at elevated temperatures in all solvents tested. The inherent viscosities of the polyimides also exhibited a descending order PD-43 > PD-11 > PD-45 > PD-44 > PD-14 > PD-41 > PD-13 > PD-15 that lies in the range of 0.372–0.875 dL/g respectively. X-ray diffraction (XRD) analysis premeditated the crystalline behavior of the polyimides. Furthermore thermal analysis i.e., thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) expressed enhanced thermal properties with meta-substituted fluorinated polyimides compared to their ortho-substituted analogues. Nonetheless, electrical recital of fluorinated polyimides was observed from moderate (meta) to low (ortho) dielectric constants values. Furthermore, the newly synthesized fluorinated polyimides demonstrated a low dielectric tangent loss and moisture absorption content.