Important factors controlling synthesis of imides in water

Four amine/anhydride models have been studied in order to understand the cr itical factors which control the synthesis of imides and polyimides in wate r. This synthesis method has been proposed recently as a convenient, enviro nmentally friendly method of producing both thermosetting and thermoplastic polyimides. The key starting step in the synthesis is the formation of a s alt/complex between the hydrolysed anhydride and the amine. The results fro m a combination of quantitative H-1 NMR, HPLC and DSC analysis have shown t hat the reactions are reversible, and that the important factor in driving the reaction to completion in water is the insolubility of the imide produc t. Analysis of the precipitated imides shows them to be free of significant amounts of the considerably more water soluble amic acids (i.e. the uncycl ized amide acids), which often contaminate imides made in conventional apro tic solvents. Of the models investigated, only the imidization of the secon d amino group in 2,4,6-trimethyl-1,3-phenylene diamine (TMPDA) was subject to kinetic control. A general conclusion from these experiments is that where a different resul t is observed in water synthesis of imides compared with conventional aprot ic solvent synthesis, it is likely to reflect the vastly different solvatio n powers of the two solvents rather than a difference in reaction mechanism .