Condensation of aldehyde with primary amine or secondary amine afforded imine or aminal bonds respectively. These bonds can undergo dynamic exchange in solution and in polymer. We investigated the synthesis of polyimine networks by condensation polymerization of poly(ethylene glycol) bis(3-aminopropyl) with 1,3,5-triformylbenzene with an equal molar ratio of amine and aldehyde functionalities in organic solvents with varying polarity and in neat condition. Their stress-relaxation and self-healing behaviors have been characterized. It was found that imine bond exchange can occur either by a dissociative or an associative pathway, with the latter being kinetically dominant in the polymer networks and catalyzed by primary amine residues. The malleability of the polyimine gels can be correlated to the imine bond exchange rate in different solvents, indicating the molecular basis for the dynamical behavior of the polymine network. Similarly, we also investigated the synthesis of polyaminal network by condensation of secondary amines (i.e., piperidine, morpholine) and mono aldehydes (i.e., formaldehyde, benzaldehyde). The aminal bond exchange in toluene solution at room temperature is accelerated by protic acids. By contrast, at high temperature in the polymer network, a catalytic amount of secondary amine appears to increase the aminal bond exchange. The dynamic thermal mechanical analysis of the polyaminal networks also revealed a gradual stress relaxation with increasing temperature, consistent with vitrimer networks where dynamic bond exchange occurs by an associative pathway.

Investigating the dynamic imine and aminal bond exchange towards covalent adaptable networks

254th National Meeting (2017)

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