Isothermal and isoconversional modeling of solid-state nitroso polymerization

The solid-state formation of azodioxide polymers from aromatic dinitroso compounds with different spacer groups was used as a model reaction for a comprehensive analysis that included bulk-based, mechanistic, and isoconversional kinetic methods. Dinitroso species were prepared in situ from azodioxides by UV cleavage under cryogenic conditions, after which their thermally induced conversion to azodioxides was followed by Fourier transform IR spectroscopy. The obtained data were used to calculate activation parameters and determine the influence of the spacer on the kinetics. Isoconversional models suggest a distribution of activation energies, pointing to an important (topochemical) effect of the local environment on the reactivity. In general, bulk-based and isoconversional kinetic models gave poorer fits but produced mutually consistent rate parameters. Similar energies and entropies of activation were obtained with all three approaches, suggesting that they all describe the same underlying physical phenomena; that is, the polymerization by bond-making is the dominant process.