Synthesis and properties of copolyimides containing naphthalene group

Several series of copolyimides were synthesized from various ratios of two diamines with aromatic tetracarboxylic dianhydrides through thermal imidization process to determine the effect of naphthalene ring on the physical properties of polymers. The copolyimides were characterized using inherent viscosity, differential scanning calorimetry (DSC), TGA, DMA, TMA and dielectric analyzer. DSC showed only a Tg and exhibited that the copolyimides had a low entropy, amorphous state and formed random polymers. They retained high modulus even at high temperatures by DMA, and had measured coefficients of thermal expansion in the range of 15–57 ppm by TMA. The glass transition temperatures (Tg) of all polymers were found to be 287–321 °C by DSC. Their decomposition temperatures at 10% weight loss in nitrogen atmospheres were above 556 °C. These polymer films had dielectric constants ranging from 2.9 to 3.4 with moisture absorptions of less than 2.65%.