Dynamic Curing Agents for Amine-Hardened Epoxy Vitrimerswith Short (Re)processing Times
2020
This
work presents a straightforward strategy to introduce highly
dynamic and adaptable cross-links into common epoxy resin formulations.
For this, an oligomeric amine-based curing agent containing vinylogous
urethane (VU) bonds was developed. This novel polyfunctional amine
curing agent can be used as a drop-in solution for existing epoxy
resin technologies, resulting in transparent, rigid, and, at the same
time, highly reprocessable catalyst-free epoxy vitrimers. The oligomeric
VU-curing agents are prepolymerized via a straightforward condensation
reaction between acetoacetates extended with different classical amine
monomers and epoxy hardeners. It is found that vitrimer properties
can be readily introduced into these epoxy formulations by converting
<50 mol % of the hardener’s amine functionalities into dynamic
vinylogous urethane bonds. In this way, epoxy vitrimers can be obtained
with material properties comparable to ones of the VU-free epoxy formulations.
In addition, remarkably short processing times are observed in the
absence of any catalyst, and the material displayed very short stress
relaxation times and good recyclability, actually representing the
most performant VU-based vitrimers so far. Furthermore, a proof of
concept for its use in obtaining glass-fiber-reinforced epoxy composites
is also presented.
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