Presidential Green Chemistry Challenge: 2012 Academic Award (Waymouth and Hedrick)
Professor Robert M. Waymouth of Stanford University
Dr. James L. Hedrick of IBM Almaden Research Center
Organic Catalysis: A Broadly Useful Strategy for Green Polymer Chemistry
Innovation and Benefits: Traditional metal catalysts required to synthesize polyesters and other common plastics end up trapped in the plastic, raising human health and environmental concerns. Professor Waymouth and Dr. Hedrick discovered an array of alternatives—metal-free catalysts—that are highly active and able to make a wide variety of plastics. Their discoveries include catalysts that can depolymerize plastic and enable cradle-to-cradle recycling.
Summary of Technology: Catalysis is a foundation for sustainable chemical processes, and the discovery of highly active, environmentally benign, catalytic processes is a central goal of green chemistry. Conventional routes to polyesters rely on metal catalysts such as those derived from tin complexes, even though the residual metal catalysts used for high-volume plastics can have negative environmental impacts in solid waste. For this reason, the European Union recently phased out many organotin compounds. As a result, research on organic catalysts to replace the tin-based workhorse catalysts has gained significant prominence in industrial settings related to important commodity polymers such as siloxanes, urethanes, nylons, and polyesters.
Dr. James L. Hedrick and Professor Robert M. Waymouth have developed a broad class of highly active, environmentally benign organic catalysts for synthesizing biodegradable and biocompatible plastics. Their technology applies metal-free organic catalysts to the synthesis and recycling of polyesters. They discovered new organic catalysts for polyester synthesis whose activity and selectivity rival or exceed those of metal-based alternatives. Their approach provides an environmentally attractive, atom-economical, low-energy alternative to traditional metal-catalyzed processes. Their technology includes organocatalytic approaches to ring-opening, anionic, zwitterionic, group transfer, and condensation polymerization techniques. Monomer feedstocks include those from renewable resources, such as lactides, as well as petrochemical feedstocks. In addition to polyesters, Dr. Hedrick and Professor Waymouth have discovered organocatalytic strategies (1) to synthesize polycarbonates, polysiloxanes, and polyacrylates, (2) to chemically recycle polyesters, (3) to use metal-free polymers as templates for inorganic nanostructures for microelectronic applications, and (4) to develop new syntheses for high-molecular-weight cyclic polyesters. This team has shown that the novel mechanisms of enchainment brought about by organic catalysts can create polymer architectures that are difficult to synthesize by conventional approaches.
The team also developed organic catalysts to depolymerize poly(ethylene terephthalate) (PET) quantitatively, allowing recycling for PET from bottles into new bottles as a way to mitigate the millions of pounds of PET that plague our landfills. Dr. Hedrick and Professor Waymouth also demonstrated that their organic catalysts tolerate a wide variety of functional groups, enabling the synthesis of well-defined biocompatible polymers for biomedical applications. Because these catalysts do not remain bound to the polymer chains, they are effective at low concentrations. These results, coupled with cytotoxicity measurements in biomedical applications, highlight the environmental and human health benefits of this approach. Professor Waymouth and Dr. Hedrick have produced over 80 manuscripts and eight patents on the design of organic catalysts for polymer chemistry with applications in sustainable plastics, biomedical materials, and plastics for recycling.
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