Synthesis and Characterization of New Polyimides Based on 3,6-Bis(4-aminophenoxy)benzonorbornane

A novel benzonorbornane-based dietheramine monomer, 3,6-bis(4-aminophenoxy)benzonorbornane (BAPBN), was prepared in two steps from aromatic nucleophilic chloro-displacement reaction of p-chloronitrobenzene with the potassium phenolate of 3,6-dihydroxybenzonorbornane, followed by hydrazine catalytic reduction of the intermediate dinitro compound. A series of benzonorbornane-based polyimides were prepared from the diamine BAPBN with various aromatic dianhydrides via a conventional two-stage synthesis in which the poly(amic acid)s obtained in the first stage were heated stage-by-stage at 150300°C to give the polyimides. The intermediate poly(amic acid)s had inherent viscosities between 0.58 and 2.03 dL/g. Almost all the solution-cast poly(amic acid) films could be thermally converted into flexible and tough polyimide films with good tensile properties. Some polyimides with more flexible backbones exhibited good solubility in polar organic solvents. Depending on the structures of the dianhydrides, the glass-transition temperatures (T_g) of these polyimides were recorded between 209 and 327°C by differential scanning calorimetry (DSC) or dynamic mechanical analysis (DMA), and the softening temperatures (T_s) determined by thermomechanical analysis (TMA) stayed in the 197320°C range. Decomposition temperatures for 10% weight loss all occurred above 480°C in both air and nitrogen atmospheres. The polyimides also showed low dielectric constants (2.62–3.53 at 1 MHz). For the comparative purpose, a series of corresponding polyimides based on l,4-bis(4-aminophenoxy)benzene (BAPB) was also prepared and characterized.