Tuning the Dynamics of Enamine-One-Based Vitrimers through Substituent Modulation of Secondary Amine Substrates

Polymer networks embedded with dynamic covalent bonds have been demonstrated to be capable of network reconfiguration. This reprocessability is often related to the network dynamics or flowability, the precise control of which highly depends on the underlying chemistry. Particularly, vitrimer materials flow at a constant crosslinking density because of the associative dynamic chemistry involved. Here, we report the fabrication of enamine-one vitrimers through an amino-yne click reaction using secondary amine substrates. Compared with primary amines, the secondary amine-based amino-yne click reaction is mild and yields less gel content (70 vs 97%) in our curing system. By modulating the substituents of the secondary amine, we show that the activation energy of the exchange reaction increases (52-90 kJ/mol) with increasing steric hindrance (piperidyl similar to methyl < ethyl < isopropyl < tert-butyl), and a similar trend was observed in the vitrimer networks. Interestingly, piperidine exhibits reactivities (including the yielded gel content and network dynamics) comparable to that of primary amines because of the less steric hindrance related to the constrained cyclic structure. This study not only enriches the scope of amine substrates for vitrimer fabrication but also offers a convenient means to tune the network dynamics through substrate choices or combination strategies (i.e., mixing primary and secondary amines or various secondary amines).