13WWW.CEN-ONLINE.ORG FEBRUARY 15, 2010

A NEW STRATEGY FOR producing propylene- and longer α-olefin-based polymeric materials promises to boost efficiency of polymer syn-

thesis and produce materials with highly controlled polyolefin chain lengths and properties. The process, developed by Lawrence R. Sita and coworkers of the University of Maryland, gives chemists access to previ-ously unattainable oils and waxes that could be useful in specialty chemical applications, including deter-gents, lubricants, and plasticizers.

“While millions of tons of linear α-olefins are pro-duced each year based on ethylene, the corresponding and potentially more interesting derivatives based on propylene or higher α-olefins have not been prepared in a robust fashion,” says polymer scientist Craig J. Hawker of the University of California, Santa Barbara. “The present work circumvents previous challenges and delivers a low-temperature, highly controlled process that has great potential in both academic and industrial laboratories.”

Sita’s group relied on two existing polymerization techniques to develop the new strategy. The first is liv-ing Ziegler-Natta polymerization of α-olefins, which typically involves continuous growth of a single poly-mer chain on each transition-metal catalyst molecule. The second technique, chain-transfer polymerization, relies on transferring the polymer chain to an inactive main-group metal alkyl, such as diethylzinc, to termi-nate growth of one chain and initiate growth of a new one. Polymer chemists have recently figured out how to make the chain transfer reversible, thereby opening new avenues to polymer and copolymer production.

Building on the reversible-chain-transfer concept, Sita, Jia Wei, and Wei Zhang use aluminum and zinc reagents in combination with a hafnium catalyst that produces poly-propylene as a work-around solution to the one-chain-per-metal restric-tion of living polymerization ( Angew. Chem. Int. Ed., DOI: 10.1002/anie.200906658). “All three metals must act in concert to pull off the precise chemistry,” Sita says.

During polymerization, propene monomer units insert between hafnium and the existing polypropylene chain, Sita explains. The growing chain exchanges rap-idly with an oligomer chain residing on the aluminum surrogate by way of the zinc reagent.

The rates of Hf–Zn/Zn–Al transfer are much faster than direct Hf–Al exchange, and all the chain-transfer rates are faster than the propene insertion step, Sita notes. These properties allow multiple propylene oli-gomer chains to grow at the same rate, giving exquisite control over low molecular weights and narrow mo-lecular weight distributions.

The nature of the chemistry allows preparation of block copolymers and end-group functionalization of oligomers, he adds, such as making long-chain, highly branched alcohols. Sita believes strongly enough in the prospects for the new chemistry that he has helped establish a company, Precision Polyolefins, to commer-cialize the technology. —STEVE RITTER

The nation will have a new climate agen-cy akin to the National Weather Service if Congress approves a reorganization plan for NOAA.

The proposed NOAA Climate Service would provide data to companies, local governments, farmers, and the public about projected changes in climate, such as alterations in rainfall patterns, Commerce Secretary Gary Locke says. NOAA, which is a Commerce Department agency, gets millions of requests for this

sort of information each year, he adds. “By providing critical planning infor-

mation that our businesses and our com-munities need, NOAA Climate Service will help tackle head-on the challenges of mitigating and adapting to climate change,” Locke says. “In the process, we’ll discover new technologies, build new businesses, and create new jobs.”

The new service would stem from a re-organization of existing NOAA programs, Locke says. Congressional appropriators

would have to approve of NOAA shifting funds from current programs into the new climate service, he explains. In addi-tion, the White House will have to give a green light to the plan. Locke hopes the new service will be in place by fiscal 2011.

As NOAA moves ahead, Congress is also considering legislation to create a national climate service, which would get input from a swath of federal agencies in addition to NOAA (C&EN, July 6, 2009, page 23). —CHERYL HOGUE

GOVERNMENT National Oceanic & Atmospheric Administration proposes new climate service

NEWS OF THE WEEK

PRECISE ROUTE TO POLYPROPYLENES

POLYMER CHEMISTRY: Novel chain-transfer process expands

range of possible materials

HfN

N

n

+

Znn n

n

Al

n

n

Chain transfer mediator(small amount)

Active catalyst/chain growth

Surrogate chain growth(large excess)

Monomer

Propene insertion(slowest)

Hf–Alchain transfer

(slow)

Zn–Alchain transfer

(rapid)

Hf–Znchain transfer

(rapid)

IN CONCERT Orchestrated exchange of polypropylene

chains provides tight control over polymer formation.