Conspectus
Poor waste management and unchecked consumption underpin our current
paradigm of plastics use, which is demonstrably unsustainable in the
long term. Nonetheless, the utility and versatility of plastics suggest
that the notion of a plastic-free society is also unsustainable. Responses
to this conundrum are increasing, and among these are research efforts
focused on the development of more sustainable plastics. This Account,
written by trained chemists, reflects an academic research journey
culminating in an appreciation of the importance of improving and
enabling the overarching systems that plastics exist within. Our primary
initial focus was on catalyst development because catalysts are key
drivers of sustainability by improving the efficiency and ease of
polymerization. Metal catalysts ranging in ligand structure and the
incorporated metal(s) were developed for the preparation of traditional
polyesters such as poly(lactic acid) and polycaprolactone. The central
themes in these works were stereocontrol (tacticity), efficiency (polymerization
rate), and versatility (monomer scope). Alongside insights gained
by systematically varying catalyst structure came impressive results
gained through collaboration, including the remarkably high activity
of novel heterometallic zinc catalysts toward various cyclic esters.
This catalysis work was complemented by and slowly transitioned
to a focus on polymer functionality and monomer design. Several fundamental
studies focus on polymer topology, specifically star-shaped polyesters,
tuned arm number, length, and tacticity. These reports feature emphases
on the end of life (solvolysis) and physical properties of polymers,
which were increasingly important themes as work shifted toward new
methods of incorporating functionality in polymers produced by ring-opening
polymerization. Three key highlights demonstrate this shift: the first
two rely upon the exploitation of olefin metathesis (cross- and ring-closing)
to functionalize polyesters or polyethers, and the third involves
the manipulation of ring-opening polymerization equilibrium to enable
selective monomer recovery from a polyester. Our foundational work
on 1,3-dioxolan-4-one (DOX) monomers is then discussed because this
emerging class of molecules offers a distinct synthetic pathway toward
functional polyesters, both conventional and novel. With this DOX
framework, polyesters that are usually challenging to synthesize (e.g.,
poly(mandelic acid)) are accessible because polymerization is driven
by the concomitant, controlled extrusion of small molecules (acetone
or formaldehyde).
After these polyester-focused highlights,
the foundation of our
ongoing work is presented, namely, that polymer sustainability must
be viewed from a systems-level perspective, including economic and
social components alongside the environmental considerations. Material
design must be driven by practice, and we have to involve key players
in academia, industry, and government in a concerted effort t...