Aliphatic polyimides containing adamantyl units (APIs) were prepared by the poly(addition/condensation) of a dianhydride bicycle[2.2.2] octane-2,3,5,6-tetracarboxylic 2,3:5,6-dianhydride with a rigid diamine, 1,3-diaminoadamantane or 3,3'-diamino-1,1'-biadamantyl, and a flexible diamine, 4,4'-methylenebis(cyclohexylamine) or 1,4-cyclohexanediamine. One-step polymerizations were conducted at 80-200 degrees C in m-cresol, producing APIs with inherent viscosities up to 0.53 dL g(-1). These APIs are soluble in haloalkanes, m-cresol, and sulfuric acid and show high thermal stability and excellent transparency.