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

Abstract

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 ( Tg) of PIs with two tert-butyl substitutes can be reached at 327.7°C, and the 5% weight loss temperatures of PI derived from CBDA were lowest at 439.7°C. These PI films had cutoff wavelengths between 301.2 and 400.0 nm and the transparency at 450 nm 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 Tg of PIs, but decreased the optical transmittance and thermal stability of PIs.