In this work, we introduced Lewis Pair (LP) reversible interactions in vinylogous urethane covalent adaptable networks (VU-CANs) as a tool to control their rheological properties through the simultaneous release of a primary amine and Lewis acid catalyst. The formation of LP within the material between free primary amine and boron-based Lewis Acids (LAs), including different triaryl and one trialkylborane (BR 3 ) was confirmed by combining small molecule studies, 11 B solid NMR, and extensive rheological characterizations. Depending on Lewis acid strength and steric hindrance, different behaviors were observed. Aryl substituents were found necessary to achieve suitable stability for both network synthesis and reprocessing. Highly acidic B(C 6 F 5 ) 3 promoted the covalent exchange even at moderate temperature, but no latency was observed. The introduction of mild LAs such as B(Ph) 3 or B(mes) 3 led to VU-CANs with low creep up to 150 °C and fast exchange at 200 °C but also superior stability at high temperature by limiting undesired amidation side reactions.
Arnould et al. (Sun,) studied this question.