Epoxy/dicarboxylic acid vitrimer
was prepared by the solvent-free
reaction of diglycidyl ether of bisphenol A (DGEBA) and 1,4-cyclohexane
dicarboxylic acid (CHDA) with the addition of monobutyltin oxide (Sn)
as a catalyst. By tailoring the catalyst content (≥5 mol %),
an effective conversion of functional groups during cure demonstrated
the network polymerization mechanisms and a sequence of the side reactions.
Indeed, the manufactured vitrimers exhibit creep and full stress relaxation
thanks to catalytic transesterifications. By changing the epoxy/diacid
ratio, the thermo-mechanical properties and mechanical behavior of
the epoxy/acid vitrimers can be tuned while keeping self-healing ability.
At high epoxy excess, both glass-transition temperature (T
g) and solid–liquid viscoelastic transition temperature
(T
v) shift to a higher temperature. At
vitrimer formulations 1:0.6 and 1:0.5 (epoxy/acyl), a remarkable improvement
of fracture toughness (K
Ic) is observed,
indicating the transition from stiff to relatively ductile materials
at 1:0.6. This is attributed to the altered network structures due
to etherification and epoxy homopolymerization. The rough fracture
surface suggests more energy dissipation during crack propagation
in vitrimer with a high excess epoxy. After healing, welded vitrimers
still exhibit good fracture toughness with only a slight reduction
(<10%) in K
Ic. We believe that these
vitrimer formulations are promising as matrices in the composite fields.
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