Polyamides (PAs) and polyimides (PIs) containing two silarylene units were synthesized and characterized by their spectroscopic properties. Bis(4-aminophenyl)methylphenylsilane was employed as a unique diamine, whereas acid dichloride and dianhydride monomers contained combinations of methyl and phenyl groups bonded to the silicon atom. The PAs were obtained in dimethylformamide solutions, and the PIs were prepared by thermal cyclization of the respective poly(amic acid)s (PAAs). The yields were low (32-51%), and the inherent viscosities for PAAs were slightly higher than the PA values. The low inherent viscosities were indicative of oligomeric species. The thermal stability was also evaluated by thermogravimetric analysis and differential scanning calorimetry analysis. In both series, the glass-transition temperatures increased with the replacement of methyl groups by aromatic rings according to the lower mobility of the polymeric chain. On the other hand, an increase in the aromatic content also increased the thermal stability of the PAs and PIs, and this was registered through their thermal decomposition temperatures. (C) 2008 Wiley Periodicals, Inc.