Synthesis, characterization and thermal studies of wholly aromatic poly(imide-amides) containing si and/or Ge in the main Chain

Poly(imide-amides) (PIAs) containing the heteroatoms Si and/or Ge in the main chain were obtained from diacids, which were synthesized from trimellitic anhydride and the diamines bis(4-aminophenyl) diphenylsilane or bis(4-aminophenyl)diphenylgermane. With the same diamines the polymers containing the heteroatoms Si and Ge in the main chain were obtained. Polymers were soluble in aprotic polar solvents and characterized by IR and ₁H, ₁₃C and ₂₉Si NMR spectroscopy, and the results were in agreement with the proposed structures. Low inherent viscosity values (η_inh) (0.04 - 0.12 dL/g) were obtained, indicating the presence of oligomeric species. The Tg values were obtained by differential scanning calorimetry (DSC), and the results did not show a relation with the nature of the heteroatoms, in the sense that the polymers with Si should have higher Tg values than those with Ge due to the lower volume of the former atom. Also, the low values of η_inh associated to low molecular weight species, have important influence on Tg values. The thermal decomposition temperatures were obtained by dynamic thermogravimetry. These analyses showed that the highest thermal decomposition temperature (TDT) values were obtained for PIA-II and PIA-III with Si and Ge in the repeating unit, and the lowest TDT values with two Si atoms in the unit.