The entire life cycle of a synthetic
polymer includes various stages
many of which involve the usage of catalysts. However, the need to
isolate intermediate products and remove catalysts at various stages
can decrease the efficiency and increase the environmental impact
of synthetic processes. In this paper, a tandem catalysis concept
was introduced in which a single catalyst enabled multiple catalytic
transformations ranging from monomer and polymer synthesis to postpolymerization
modifications and polymer property modulation through curing and transesterification.
Specifically, a simple and readily available Mn–salen complex
could catalyze copolymerization of epoxides with unsaturated cyclic
anhydrides to synthesize unsaturated polyesters; epoxidation or ring-opening
aminolysis to generate epoxy- or arylamine-functionalized polyesters;
curing of the epoxy-functionalized polyesters with cyclic anhydrides
to prepare cross-linked epoxy resins; transesterification-induced
dynamic exchange of cross-links in the epoxy resins to afford a vitrimer
system. This tandem catalysis system required minimum workup and intermediate
isolation, making it a highly efficient method to prepare novel polymers
with various properties.
Functionalization
and reinforcement of polymers by introducing
dynamic sacrificial bonds have attracted increasing attention. In
this contribution, the in situ modification of isoprene rubber by
the formation of sacrificial bonds during vulcanization has been investigated.
The sacrificial bonds were formed by in situ introduction of hydrogen
bonds and metal–ligand motifs, which became part of the vulcanized
isoprene rubber network by reaction of the former with the vulcanizing
agent. The introduction of three-component modifiers (nadic anhydride
(NA), 2-aminopyrimidine (AP), and ZnCl2) and the molar
ratio of these components can greatly affect the tensile strength
and modulus of the vulcanized rubber. Under the external load, the
sacrificial bonds preferentially rupture prior to the covalent network
and facilitate rubber chain orientation, resulting in high fracture
energy. In addition, the dynamic behavior of the sacrificial bonds
and the hysteresis behavior of the vulcanized rubbers were studied.
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