Reversible crosslinking offers an attractive strategy
to modify
and improve the properties of polymer materials while concurrently
enabling a pathway for chemical recycling. This can, for example,
be achieved by incorporating a ketone functionality into the polymer
structure to enable post-polymerization crosslinking with dihydrazides.
The resulting covalent adaptable network contains acylhydrazone bonds
cleavable under acidic conditions, thereby providing reversibility.
In the present work, we regioselectively prepare a novel isosorbide
monomethacrylate with a pendant levulinoyl group via a two-step biocatalytic
synthesis. Subsequently, a series of copolymers with different contents
of the levulinic isosorbide monomer and methyl methacrylate are prepared
by radical polymerization. Using dihydrazides, these linear copolymers
are then crosslinked via reaction with the ketone groups in the levulinic
side chains. Compared to the linear prepolymers, the crosslinked networks
exhibit enhanced glass transition temperatures and thermal stability,
up
to 170 and 286 °C, respectively. Moreover, the dynamic covalent
acylhydrazone bonds are efficiently and selectively cleaved under
acidic conditions to retrieve the linear polymethacrylates. We next
show that recovered polymers can again be crosslinked with adipic
dihydrazide, thus demonstrating the circularity of the materials.
Consequently, we envision that these novel levulinic isosorbide-based
dynamic polymethacrylate networks have great potential in the field
of recyclable and reusable biobased thermoset polymers.