Thermally Annealed Solid State Polymerization of 2,3-Dicyano-5,7-Dimethyl-6H-1,4-Diazepine: An NMR Study

Abstract

The thermally annealed solid state polymerization of 2,3-dicyano-5,7-dimethyl-6H-1,4-diazepine(A) was studied by 1 H, 13 C, and 15 N CP=MAS solid state NMR spectroscopy, and by a 1 H solution state NMR deuterium exchange experiment of A. Collectively, the NMR data suggests that a tautomeric form of the monomer is responsible for the solid state reactivity of the crystalline monomer. The solid state polymerization of crystalline A proceeds as a heterogeneous decomposition of the crystalline lattice resulting in an insoluble, amorphous material. A plausible reaction scheme involving a tautomeric form of A is proposed. The scheme is consistent with the NMR spectra.