A series of new poly(amide-imide)s were synthesized by direct polycondensation of 4,9-bis(trimellitimido)diamantane (1) with various aromatic diamines in N-methyl-2-pyrrolidone (NMP) containing lithium chloride. The poly(amide-imide)s had medium and high number-average molecular weights (M-n) of 79 000-255 000. The new polycyclic monomer 1 was synthesized from 4,9-diaminodiamantane with trimellitic anhydride. Dynamic mechanical analysis (d.m.a.) revealed that the glass transition of the poly(amide-imide) derived from 4,4＇-oxidianiline appeared at similar to 290 degrees C. D.m.a. results also indicated that poly(amide-imide)s remained stable at high temperatures and maintained good mechanical properties (G＇ > 10(8) Pa) up to high temperature (300 degrees C). Most of the poly(amide-imide)s were soluble in NMP, N-dimethylacetamide (DMAc) and o-chlorophenol. Most were cast into flexible films which had tensile strengths ranging from 35.6 to 52.5 MPa, elongation-to-breakage from 3.5 to 7.9%, and initial moduli from 1.9 to 2.1 GPa. The temperatures at 5% weight loss ranged from 423 to 435 degrees C in air and from 438 to 471 degrees C in N-2.