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 °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 -butylbenzene indicates that the symmetric compound leads to the strong intermolecular interaction and good packing ability. In the 1 H 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.