CAS: Sustainable Polymers via Amide to Ester Polymerization (ATEP)

With the support of the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Professor Stephen A. Miller of the University of Florida will convert post-consumer waste plastic and bio-based feedstocks into a novel family of sustainable polymers with properties suitable for replacing incumbent packaging plastics. Despite what is taught in most textbooks, the ester functional group is generally more stable than the amide functional group, as proof of concept experiments and computations indicate.

This relative stability will be exploited to synthesize exemplary polymers via Amide to Ester Polymerization (ATEP), an unexplored polymerization pathway particularly suited for the chemical recycling/upcycling of post-consumer polyesters (e.g., water bottles and polyester clothing) and nylons (e.g., backpacks and fishing nets), yielding polyesteramides. Convergent chemical recycling will transform mixed waste streams of polyesteramides and polyesters into a single monomer suitable for repolymerization.

Alternatively, the polyesteramides will be degraded via hydrolysis under environmentally relevant conditions (e.g., seawater). Long-term studies will establish polyesteramide degradation rates, while computational studies will explain how they can degrade in water over relatively short timescales—necessary to combat the plague of plastics accumulating in the environment.

The U.S. plastics industry directly employs over one million people and generates $550 billion in annual shipments. More sustainable polymers—whether from post-consumer materials or bio-based feedstocks—are expected to exceed a 40% market share by 2030. Inclusion of the proposed ATEP polymers could further accelerate this amazing growth and expand the variety of materials applications.

While polyester aminolysis is much more facile than hydrolysis or alcoholysis, the formed bis-amides have minimal demand because of their presumed stability. ATEP creates an application for these bis-amides and is a novel kinetic pathway for their polymerization, generally yielding polyesteramides with properties excelling those of the original polyester.

Key polymer properties include melting temperature and glass transition temperature, and these measured properties will be correlated to polymer structure. For example, aminolysis of post-consumer PET (polyethylene terephthalate) followed by ATEP will yield polyesteramides with a tunable glass transition temperature that depends on the nature of the amine originally employed for aminolysis.

Polymer upcycling will be achieved when the glass transition temperature substantially excels that of the precursor PET (72 °C). The complexities of ATEP will be unraveled by pursuing specific project goals: (1) optimizing PET aminolytic depolymerization conditions and applying them to a variety of commodity polymers, including polyesters, nylons, and others; (2) optimizing ATEP and comparing polyesteramide properties to those of extant polymers; (3) further developing the thermodynamic and kinetic rationale of ATEP via computational methods; (4) applying ATEP to a variety of bio-based diacids; (5) establishing polyesteramide structure/property relationships; and (6) investigating practical depolymerization conditions, including environmental degradation and chemical recycling.

Exploring the many facets of ATEP will greatly expand the fundamental understanding of polymerization/depolymerization chemistry.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.