A series of new polyimides (PIS) containing di-tert-butyl side groups were synthesized via a polycondensation of 1-(4-aminophenoxy)-4-(4-amino-2-methylphenyl)-2,6-di-tert-butylbenzene (3) with various aromatic tetracarboxylic dianhydrides. The novel unsymmetric PIs exhibited a low dielectric constants (2.78-3.02), low moisture absorption (0.53-1.35%), excellent solubility, and high glass transition temperature (308-450 degrees C). The PI derived from the new diamine and the very rigid naphthalene-1,4,5,8-tetracarboxylic dianhydride (NTDA) was soluble in N-methyl-2-pyrrolidone, chloroform, in-cresol, and cyclohexanone. The unsymmetric di-tert-butyl pendent groups significantly enhance the rotational barrier of the polymer chains; thus these PIS had high T(g)s. The H-1 NMR spectrum of the diamine 3 revealed that 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. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 24432452,2009