Low Dielectric Constant and High Organosolubility of Novel Polyimide Derived from Unsymmetric 1,4-Bis(4-aminophenoxy)-2,6-di-tert-butylbenzene

A series of new polyimides (PIs) containing tert-butyl side groups were synthesized via a polycondensation of 1,4-bis(4-aminophenoxy)-2,6-di-tert-butylbenzene (4) with various aromatic tetracarboxylic dianhydrides. The introduction of the asymmetric di-tert-butyl groups is an effective way to increase the interchain distance and decrease in the intermolecular force and packing ability of the resulting polymers. Thus, this novel Pis exhibit a low dielectric constant (2.74-2.92), low moisture absorption (0.32-1.53%), excellent solubility, and high glass transition temperature (276-398 degrees C). The Pis derived from the very rigid pyromellitic dianhydride (PMDA) were soluble in N-methyl-2-pyrrolidone, N,N-dimethylacetamide, chloroform, tetrahydrofuran, and cyclohexanone. The crystal structure of 1.4-bis(4-phthalimidophenoxy)-2,5-di-tert-butyl benzene indicates that the symmetric compound leads to the strong intermolecular interaction and good packing ability. In the H-1 spectrum of the diamine 4, the protons of 4-aminophenoxy moiety are not chemical shift equivalent. This is because the steric hindrance of the bulky di-tert-butyl groups prevents the benzene ring of 4-aminophenoxy moiety from rotating freely. In addition, the effect of symmetric and asymmetric di-tert-butyl pendent groups on the properties of Pis was discussed.