Synthesis and characterization of oxyethylene containing diisocyanates and polyimides therefrom

A facile synthesis of a series of oxyethylene containing diisocyanates, the α,ω‐bis(isocyanatophenoxy)alkanes and bis[2‐(isocyanatophenoxy)ethyl] ethers, is described. The key step involves the uneventful decomposition of the corresponding diacylazides to the diisocyanates in the Curtius rearrangement reaction. Further, eight thermally stable oxyethylene containing polyimides were synthesized by the polycondensation reaction of two meta‐ and two para‐oriented diisocyanates, namely, 1,2‐bis(3‐isocyanatophenoxy)ethane and 1,2‐bis(4‐isocyanatophenoxy)ethane, and bis[2‐(3‐isocyanatophenoxy)ethyl] ether and bis[2‐(4‐isocyanatophenoxy)ethyl] ether, with pyromellitic dianhydride (PMDA) and benzophenonetetracarboxylic dianhydride (BTDA) in N,N‐dimethylacetamide (DMAc). These polyimides were characterized by IR spectroscopy, x‐ray diffraction, viscosity measurements, and thermogravimetric analysis.