A new diacid monomer containing a pendent adamantyl ring was reacted with various aromatic diamines to prepare novel aromatic polyisophthalamides (PIPAs). The polymers were obtained in high yield and high molecular weight by the Yamazaki-Higashi phosphorylation method of polycondensation. Inherent viscosities ranged from 0.40 to 0.82 dL/g, which corresponds to weight-average and number-average molecular weights (GPC) in the range 21,000-63,000 g/mol and 9000-31,000 g/mol, respectively. The polymers were essentially amorphous and soluble in a variety of polar aprotic solvents, and they afforded transparent, creasable films by the solution-casting method. The great size of the polyhedral adamantyl moiety brought about a significant restriction of segmental mobility, which translated into a strong increase of T-g, so that very high glass transition temperatures were observed, in the range 335-370 degrees C (DSC), which are 70-90 degrees C above the glass transition temperatures of homologous PIPAs without pendent groups. Thus, it can be stated that these adamantyl containing polyamides are among the soluble aromatic PIPAs with highest T-g ever described. Conversely, the initial decomposition temperature, as measured by thermogravimetric analysis, was about 400 degrees C, which is lower by 40-70 than that of unsubstituted counterparts. Polymer films exhibited good mechanical properties, with tensile strengths over 65 MPa and tensile moduli between 2.0 and 2.6 GPa. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1743-1751, 2010