The Chemical Catalysis Program supports Professor Robert M. Waymouth at Stanford University and Dr. James L Hedrick at IBM for a research project that will explore new patterns of reactivity of organic catalysts for controlled polymerization reactions. Specific objectives are to: (1) develop novel bifunctional strategies for organocatalytic polymerization reactions; (2) develop a detailed kinetic and mechanistic understanding of zwitterionic polymerizations for the synthesis of macrocyclic polymers; and (3) develop new organocatalytic methods for the synthesis of biodegradable and biocompatible polyphosphates. The zwitterionic polymerization mediated by N-heterocyclic carbenes is a new conceptual advance for the enchainment of monomers to high molecular weight cyclic polymers. Mechanistic and kinetic insights on the details of these reactions will provide a conceptual and quantitative picture of the scope, power and limitations of this new synthetic method. Organocatalytic polymerization strategies provide an environmentally friendly approach for the synthesis and recycling of major commodity polymers. Mechanistic insights on new mechanisms of enchainment will create new opportunities for the generation of novel polymer architectures, including new families of polyphosphates for biomedical applications.
With the support of the Chemical Catalysis Program in the Chemistry Division at the National Science Foundation, Drs. Waymouth and Hedrick will perform research that will provide new catalytic strategies for the design of biodegradable polymers derived from renewable resources. New synthetic methods developed as part of this program will enable new strategies for the synthesis of well-defined polymer architectures. These developments will enable studies of the role of polymer structure on properties and function, issues that are fundamental to our understanding of chemistry and to the application of macromolecules in modern technologies. Broader impacts include involving students in an exceptional training environment involving a highly interdisciplinary and collaborative effort between an academic institution and an industrial laboratory. The PIs have taken an active role in recruiting and mentoring underrepresented minorities and disabled students. In addition, IBM is committing significant resources to this effort, including laboratory and office space for a postdoctoral coworker and visiting Stanford students, materials and supplies, extensive access to IBM facilities and infrastructure as well as 25% of Dr. Hedrick's time.
The goal of this project was to investigate new environmentally-benign methods for generating biodegradable and biocompatible plastics. Plastics, our versatile modern materials, are almost exclusively derived from petrochemical sources, but the finite supply of fossil fuels and environmental impact of petroleum-based technologies highlight the need for the development of alternative strategies to provide the materials, products, and technologies that improve our lives while preserving the environment for future generations. In this highly collaborative effort between the academic laboratory of Robert Waymouth at Stanford University and the industrial laboratory of Dr. James Hedrick of IBM, this project pioneered new catalytic methods for generating polyesters utilizing small organic molecules as catalysts. As most polyesters are made with metal catalysts, this provides a distinctive approach for generating degradable plastics devoid of metal residues. We have also shown that these organic catalysts can be used to degrade polyester plastics back to their building blocks, providing a potential strategy for recycling commercial plastics such as poly(ethylene terephthalate) (PET). This project involved fundamental scientific studies on the chemical reactivity of organic catalysts as well as translational studies to apply the insights from these studies to devise new strategies for generating new classes of plastics from renewable resources, or selectively degrading these materials. The intellectual merit of the project included both fundamental insights on organic catalysis and its utility in generating new plastics as well in providing innovative technological options for the next generation of sustainable materials. Our fundamental studies led to a new strategy for making large cyclic macromolecules (molecular loops). Most plastics are derived from long chain-like molecules; if the ends of these long chains are connected in a cycle, the properties of the resulting materials differ from the linear analogs in ways that remain poorly understood. Our catalytic strategy for generating these large cycles is enabling us to address the basic question of how the connectivity (linear vs. cyclic) of large molecules influences their behavior. The unique reactivity of these organic catalysts allowed us to generate shorter chains containing chemical functionalities that mimic those found in naturally-occurring proteins. With these new techniques, we generated new classes of biomedical materials, including drug-delivery agents that mimic the properties of cell-penetrating peptides. These new biodegradable materials penetrate and deliver imaging probes, drugs and genetic material across cell membranes, a critical barrier to many drugs or imaging agents in biomedical research. We have also developed new strategies for generating plastics from renewable resources, providing materials that can mimic the performance of petroleum-based plastics, but with a potentially smaller environmental footprint by virtue of their biodegradability to non-toxic metabolites. Broader Impacts of the project are reflected in the worldwide interest spawned by the team's pioneering efforts in organic catalysis for green polymer chemistry. Over 44 manuscripts have been published with NSF support over the past 10 years and have generated over 2500 citations. Five patents were issued during the course of the project, illustrating the potential of fundamental scientific investigations to seed new technologies. This project has provided an unusually stimulating environment for the intellectual and professional development of the students working on this project. As a joint effort between an academic (Stanford) and industrial (IBM) laboratory, students working on the project have been exposed to highly collaborative research environment in a team effort. In addition to graduate students and postdoctoral fellows, we have taken an active role in recruiting and mentoring underrepresented minorities, undergraduates and high school students. The success of this collaborative effort was recognized by the Environmental Protection Agency in the 2012 Green Chemistry Challenge Award, awarded jointly to Professor Robert Waymouth and Dr. James Hedrick.
