Development and characterization of homo, co and terpolyimides based on BPDA, BTDA, 6FDA and ODA with low dielectric constant

Polyimides are a sophisticated family of materials, which cover an exhaustive range of high performance polymers and find applications from aerospace to microelectronics. Microelectronic applications demand low dielectric constant and high performance. Aromatic terpolyimides were synthesized by reacting 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA), 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) with 4,4′-oxydianiline (ODA) by thermal imidization with the view to decrease their dielectric constant without compromising thermal properties and mechanical properties compared to their homo and copolyimides. They were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Their FTIR spectra established formation of polyimide by the characteristic vibrations at 1375 cm-1 (C-N stretch) and 1113 cm-1 (imide ring deformation). The TGA results showed decomposition of imides at about 515°C. The glass transition temperature (Tg) of the polymers varied from 261°C to 281°C. The XRD spectrum of BPDA/BTDA/6FDA-ODA, which contained 50% of 6FDA, showed a broadened envelope with a peak at 16.8° (2θ), illustrating a semicrystalline nature. Incorporation of 6FDA, with a bulky bridging group into the backbone of BPDA/6FDA-ODA and BPDA/BTDA/6FDA-ODA (0.25:0.25:0.5::1) caused a decrease in the dielectric constant (2.13 and 2.38, respectively). Such polyimides can find application in microelectronics such as flexible printed circuits and tape automated bonding applications.