Poly(amides) and poly(imides) containing the heteroatoms Si or Ge in the main chain and bonded to four carbon atoms were synthesized and characterized by IR and H-1, C-13 and Si-29 NMR. The acid dichlorides bis(4-chloroformylphenyl)-dimethylgermane, bis(4-chloroformylphenyl)diphenylgermane, bis(4-chloroformylphenyl)-dimethylsilane, and bis(4-chloroformylphenyl)-diphenylsilane were synthesized from the ditolyl derivatives, which were oxidized to the respective diacids. The dianhydrides bis(3,4-dicarboxyphenyl)-dimethylgermane dianhydride, bis(3,4-dicarboxyphenyl)-diphenylgermane dianhydride, bis(3,4-dicarboxyphenyl)-dimethylsilane dianhydride, and bis(3,4-dicarboxyphenyl)-diphenylsilane dianhydride were synthesized from the dixylyl derivatives, which were oxidized to the tetraacids. Fully aromatic diamines also containing Si or Ge were synthesized from 4-bromo-N,N-bis(trimethylsilyl)-aniline and diphenyl-dichlorosilane or germane. The ditolyl and dixylyl derivatives were synthesized from 4-bromo-toluene or 4-bromo-xylene and dimethyl- or diphenyl-dichlorogermane, dimethyl- or diphenyl-dichlorosilane. The glass transition temperatures and the thermal stability were determined showing in general that the polymers with Si atom in the main chain presented higher values of both parameters due to the higher ionic character of the C-Si bond compared with the C-Ge one, and due to the lower size of the Si atom that presents lower rotational barriers. (c) 2006 Wiley Periodicals, Inc.