ma8b02654_si_001.pdf (1.34 MB)
Investigation of Secondary Amine-Derived Aminal Bond Exchange toward the Development of Covalent Adaptable Networks
journal contribution
posted on 2019-01-04, 00:00 authored by Albert Chao, Donghui ZhangSecondary
amine-derived aminal bonds represent an attractive class
of dynamic covalent bonds that undergo rapid exchange reaction under
mild conditions without the need of exogenous catalysts. The aminal
bond exchange occurs by a dissociative transamination mechanism in
organic media with a low activation barrier. Kinetic studies using
model compounds have revealed that the transamination pathway is catalyzed
by a protic source and involves the formation of iminium ion intermediate.
Polyaminal polymers can be readily synthesized by condensation of
multifunctional secondary amines and paraformaldehyde with a 2:1 amine-to-formaldehyde
stoichiometry. The rapid aminal exchange by transamination has given
rise to the stress relaxation and self-healing behaviors of polyaminal
thermosets. Thermodynamic measurements revealed that the aminal–iminium
equilibrium is weakly dependent on temperature, thus rendering the
polyaminal thermosets to remain as a network (above the gel points)
in a wide temperature range. This allows for remolding and reprocessing
of the fractured polyaminal networks as a solid by heating at high
temperatures, resulting in the restoration the mechanical properties
that are comparable to the undamaged polymers.