Poly(imide-amides) oligomers based on germarylene units containing amino acid moieties: Synthesis, characterization and thermal analysis

Four oligomeric poly(imido-amides) (PIAs) were obtained from dicarboxylic acids, derived from two dianhydrides containing a Ge atom and the amino acids glycine or L-alanine, which reacted with the diamine bis(4-aminophenyl)- diphenylgermane, in order to obtain the PIAs containing two Ge atoms in the main chain. PIAs which contain Me/Me or Ph/Ph on the Ge atom of the dicarboxylic acids moiety, were characterized by IR and ¹H and ¹³C NMR, and elemental analysis. The yields were over 60% with the exception of PIA-II, and the low η_inh values are indicative of low molecular weight species. Tg and the thermal stability were evaluated by DSC and thermogravimetry respectively. When L-alanine was included in the dicarboxylic acid, it was possible to see lower values of T_g with respect to those with glycine, due to the higher flexibility of the methyl side groups. When phenyl groups are bonded to the Ge atom of the dicarboxylic acid, also there is a decrease of the T_g in front of those with methyl groups, due to that the increase of the volume of the side groups affects negatively the free rotation of the polymeric chain. The TDT values were obtained by dynamic thermogravimetry, and show that these PIAs are not thermally stables materials, because the 10% of weight loss is lower than 400 °C, with the exception of PIA-IV, in which the value is 403 °C. The low thermal stability can be due to that the dicarboxylic acids are of aliphatic nature. On the other hand, there was not a clear tendency about the influence of the nature of the amino acid and the groups, methyl or phenyl, bonded to the Ge atom in the dicarboxylic acids.