Novel Miscible Blends Composed of Poly(Methyl Methacrylate) and 2,2-Bis(3,4-Carboxyphenyl)Hexafluoropropane Dianhydride-Based Polyimides with Optical Grade Clarity

Several blends of polymers that varied concentrations of poly(methyl methacrylate) (PMMA) and polyimides based on 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) were prepared in film form by solution casting and using various solvents. The miscibility of the blended films was correlated through a differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FTIR), and an image analyzer. DSC thermograms revealed two glass-transition temperatures (Tg) for specimens using tetrahydrofuran (THF) as a casting solvent, indicating immiscibility; on the other hand, samples using methyl chloride (MC) and cyclohexanone showed a single Tg, indicating miscibility between the two polymers. The phase separation temperature for the miscible samples showed lower critical solution temperature type (LCST-type) behavior and reached its minimum when the content was about 70 mass% PMMA. Both the transmittance and haze of the miscible blended films were measured according to the American Standards Testing Method (ASTM) specification D1003. The transmittance for 6FDA-6FpDA/PMMA had a value of about 85% in the visual light range. However, 6FDA-6FpDA:DABA 2:1/PMMA showed a low transmittance below wavelengths of 550 nm. For haze, all of the films were clear with values of less than 1%. The mechanical scratch resistance was measured by pencil test (ASTM 3363). Increasing the 6FDA-6FpDA polyimide content was found to increase the scratch resistance of the films.