Synthesis of oligoimides with terminal nadic groups in the presence of a new cyclizing system methyltriethoxysilane — tertiary aliphatic amine

A new method for the synthesis of reactive oligoimides with terminal nadic groups without the use of toxic reagents is proposed. The synthesis of ROI is carried out in dimethylacetamide (DMAA) in two stages without isolation of an intermediate product. Aromatic diamine is condensed in the first stage with the mixture of aromatic dianhydride and nadic anhydride at 25 °C to form oligoamidoacid. Thermochemical imidization of oligoamidoacid is carried out in the second stage in the presence of a cyclizing system of methyltriethoxysilane and diazobicyclooctane (MTEOS—DABCO) at 140 °C with the formation of oligoimides carrying terminal nadic groups. The structure of the final products was confirmed by ¹H NMR and IR spectroscopy. Bis-amidoacid 2a was obtained as an example of a model compound by condensation of 2,2-bis(4-aminophenoxyphenyl)-propane and nadic anhydride (1: 2 mol) and the kinetics of imidization was investigated. It is demonstrated that the imidization reaction is significantly accelerated in the presence of the MTEOS + DABCO system compared to the reaction in the absence of additives. Almost complete conversion of carboxyamide groups into imide cycles is achieved in 30 min, while maintaining unsaturated bonds in the terminal groups.