Here,
we report the fabrication of a dynamic enamine-one bond based
vitrimer through amino-yne click chemistry. In contrast to amine-acetoacetate
condensation, the amino-yne click reaction yields a dynamic enamine-one
motif that is composed of cis/trans (3:1) isomers and has a relatively lower activation energy (35 ±
3 kJ/mol vs 59 ± 6 kJ/mol), owing to the absence of a methyl
substituent. The resulting vitrimer network has superior mechanical
properties and faster dynamic exchange than that of a reference vitrimer
derived from amine-acetoacetate condensation, and they are attributed
to the fewer network defects and the less sterically hindered exchange
reaction, respectively. Lastly, the efficient amino-yne click reaction
is demonstrated to be compatible with the secondary-amine substrate,
which has a low reactivity toward the amine-acetoacetate condensation.
The efficient and side product-free amino-yne reaction offers a powerful
chemical tool for vitrimer fabrication and is potentially desirable
for sealing and adhesion applications.
As a class of recyclable thermoset, vitrimers are generally constructed by introducing dynamic chemistry into various synthetic or biobased building blocks. Particularly, biobased vitrimers have drawn increasing interest because of...
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 ∼ 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).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.