Effects of tert-butyl substitutes of fluorinated diamine on the properties of polyimides

To investigate the effect of tert-butyl substitutes on the properties of fluorinated polyimides (PIs), 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (1), 1,4-bis(4-amino-2-trifluoromethylphenoxy)-2-tert-butylbenzene (2), and 1,4-bis(4-amino-2-trifluoromethylphenoxy)-2,5-di-tert-butylbenzene (3), which were synthesized in this study. Three series of organosoluble and light-colored PIs were synthesized from 1, 2, and 3 with four dianhydrides 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), pyromellitic dianhydride, 3,3,4,4-biphenyl tetracarboxylic dianhydride, and 4,4-oxydiphthalic anhydride and prepared through a typical two-step polymerization method. These obtained PIs with tert-butyl substituents were soluble in amide polar solvents and even in less polar solvents. The glass transition temperatures (T-g) of PIs with two tert-butyl substitutes can be reached at 327.7 degrees C, and the 5% weight loss temperatures of PI derived from CBDA were lowest at 439.7 degrees C. These PI films had cutoff wavelengths between 301.2 and 400.0nm and the transparency at 450nm between 43.0 and 86.2%. Compared with diamine 1, we found that the introduction of tert-butyl side group of the diamine improved the solubility and T-g of PIs, but decreased the optical transmittance and thermal stability of PIs.