ANAHEIM, CALIF. -- By mimicking nature, a Cornell University chemist has found a seemingly efficient way to create a new plastic material. It would be either biodegradable or able to react with water to convert into nontoxic materials, and it would have properties such as impact resistance.
The natural system being copied is photosynthesis, nature's efficient way of extracting carbon dioxide (CO2) from the atmosphere and turning it into both monomers and polymers in the form of sugars and polysaccharides. The breakthrough, part of what is being called the second plastics revolution, is tapping the same CO2 feedstock used by plants to make synthetic polymers.
Geoffrey Coates, assistant professor of chemistry and chemical biology at Cornell, presented his findings on a new generation of catalysts for the synthesis of polymers of CO2 at the national meeting of the American Chemical Society at the Anaheim Marriott today (March 22). He will present further details on his research in a talk on Thursday (March 25).
The advance reported by Coates and his colleagues at Cornell is a zinc-based catalyst used to react CO2 and epoxide molecules to produce a class of materials called polycarbonates. An epoxide is a three-membered ring molecule, such as ethylene oxide. The resulting complex has an activity that is significantly higher than any previous catalyst in copolymerizations of CO2, Coates said. This means that for the first time the process appears to be economical and have commercial possibilities.
"This is a very rare example of a catalytic process that uses CO2 as a feedstock instead of petroleum products," Coates said.
Japanese scientists reported the copolymerization of CO2 in the 1960s, and there have been several successful attempts to produce such polymers since then, using both aluminum and zinc complexes as catalysts. But the polymerization reaction had been so slow, Coates said, that there have not been the economies of scale achievable with petroleum as a feedstock. Even catalysts developed as recently as the 1990s have poor reactivities -- only 10 molecules of CO2 could be reacted an hour. In comparison, typical petroleum feedstock reactions can combine as many as 10 million molecules an hour.
In this latest research, Coates said, "We have developed a well-defined system that exhibits unprecedented activity." One catalyst looks particularly promising, consuming more than 600 CO2 molecules an hour, he said. Furthermore, the reaction was achieved at low CO2 pressure and moderate temperatures, which could make the polymer attractive to industry. "We are at the point at which reactions now only take hours, compared to days for previous catalysts," he said.
Coates noted that the new polymer has potential application as a biodegradable material in packaging or in agricultural or biomedical materials. Difficulty of manufacture has, to date, yielded such small amounts of the polymer that a comprehensive study of its properties has not been made. He likened the stage of development of these polycarbonates to that of polypropylene when it was first produced in the 1950s. "We didn't know what to do with polypropylene. It was a new polymer with no known industrial uses. So like polypropylene, only a commercial process for making CO2-based polycarbonates will stimulate industry to find applications," he said.
However, Coates said, because of the low cost and accessibility of CO2 and the attractive properties of polycarbonates, "the development of new, efficient catalysts for the polymerization process is a significant scientific goal."
Coates was assisted in this research by Cornell graduate student Ming Cheng and staff crystallographer Emil Lobkovsky. The work is supported by the National Science Foundation and the Cornell Center for Biotechnology.
Related World Wide Web sites: The following sites provide additional information on this news release. Some might not be part of the Cornell University community, and Cornell has no control over their content or availability.
-- Geoffrey Coates: http:// www.chem.cornell.edu/department/Faculty/Coates/coates.html
-- 217th ACS national meeting, Anaheim: http://www.acs.org/meetings/anaheim/welcome.htm