Kinetic Study of the Ring‐Opening Polymerization of Diaziridines With Diamines

Polyureas spread their portfolio of applications in the last years due to their unique mechanical and chemical properties. However, the scale-up required to sustain this growing interest brings about safety and sustainability concerns. First, the possibility of avoiding the use of isocyanates is compelling. To fill this gap, an innovative isocyanate-free route has been proposed based on the step-growth polymerization of a diazirine with an aliphatic diamine. Still, the selection of an environmentally friendly solvent and the proper understanding of the kinetic mechanism of this polymerization remain as open points to be urgently cleared to favor the adoption of this appealing route. For this reason, the present work pretends to establish a safe solvent for the step-growth polymerization of N,N’-(hexane-1,6-diyl)bis(aziridine-1-carboxamide) based on the evaluation of its Hansen solubility parameters. Then, a systematic kinetic analysis is performed at different stoichiometric ratios of hexamethylenediamine and diaziridine (r) to develop a kinetic model for their co-polymerization, by deriving the rate constant associated with the reaction and its dependence from temperature. With the aid of this model, the polymer microstructure can be reliably predicted and tuned by acting on the process conditions and r, thus expanding the interest in this new class of materials.