The thermal properties of poly(esters) containing Si and/or Ge in the main chain derived from the acid dichlorides bis(4-chloroformylphenyl)-dimethyl-silane, bis(4-chloroformyl-phenyl)-dimethyl-germane, bis(4-chlorofonnyt-phenyl)-diphenyl-silane and bis(4-chloroformyl-phenyl)-diphenyl-silane, and the diphenols bis(4-hydroxyphenyl)-dimethyl-silane, bis (4-hydroxyphenyl)-dimethyl-germane, bis(4hydroxyphenyl)-diphenyl-silane and bis(4-hydroxyphenyl)-diphenyl-germane were studied by differential scanning calorimetry and dynamic thermogravimetry. Poly(esters) with two Si atoms in the main chain showed higher values of Tg than those with two Ge atoms, and the same was observed for poly(esters) with phenyl groups bonded to the heteroatoms, instead of those with methyl groups. Thermal decomposition temperatures were also higher for those poly(esters) with two Si atoms in the main chain and those in which the heteroatom is bonded to phenyl groups, due to the higher polarity of the Si-C bond in front of the Ge-C. (C) 2004 Elsevier B.V. All rights reserved.