Preparation And Properties Of Colorless And Transparent Semi-Alicyclic Polyimide Films With Enhanced High-Temperature Dimensional Stability Via Incorporation Of Alkyl-Substituted Benzanilide Units

Two colorless and transparent polyimide (CPI) films with enhanced high-temperature dimensional stability and solution-processability were prepared from the methyl-substituted benzanilide containing organo-soluble polyimide (PI) resins. For this target, a new aromatic diamine, 2,3 '-dimethyl-4,4 '-diaminobenzanilide (MMDABA) was synthesized. The methyl substituents were expected to endow the derived PI resins good solubility and rigid-rod benzanilide units can efficiently reduce the coefficients of thermal expansion (CTE) of the derived CPI films. CPI-a and CPI-b were prepared by the one-step thermal polycondensation from MMDABA with hydrogenated pyromellitic dianhydride for CPI-a and hydrogenated 3,3 ',4,4 '-biphenyltetracarboxylic dianhydride for CPI-b, respectively. The derived PI resins were soluble in polar aprotic solvents. Colorless and transparent CPI-a and CPI-b films were prepared from the PI solutions and the subsequent 280 degrees C curing. The CPI films showed good transparency in visible light and transmittances higher than 80% at 450 nm and yellowness index (b*) below 2.0. More importantly, the derived CPI-a film showed the glass transition temperature (T-g) of 417.5 degrees C and the CTE value of 46.9 x 10(-6)/K in the range of 50-250 degrees C. Apparently, incorporation of alkyl-substituted benzanilide units achieved good balance among solution-processability, high-temperature dimensional stability, and optical properties.