SIGNS OF STRESS
to polymers in solution before, but this is the first time they’ve been incorporated in solid polymers, according to Sottos. MATERIALS SCIENCE: Polymers indicate “The trick was precisely placing the mechanophore, which is a very small molecule, imminent failure by changing color into a large polymer chain,” Sottos says. She notes that her team chose a particular spiroEOPLE UNDER STRESS may exhibit certain pyran as their mechanophore because it contelltale signs that indicate they’re near a breaktains multiple potential attachment points. ing point. Some, for example, will turn bright Thus they were able to incorporate the molecule in red just before they blow their top. Now, a new polymer both a rubbery poly(methyl acrylate) polymer and a does the same thing, changing color when stressed to glassy poly(methyl methacrylate) polymer. the point of mechanical failure (Nature 2009, 459, 68). “These polymers are extremely interesting to materiSuch a material could be used as a damage sensor that als scientists since they combine photo-, thermo-, and enables researchers to assess the mechanochromic properties into a effects of stress on polymeric masingle system,” comments Stephen Polymer terials before they fail. H. Foulger, a materials science O The new polymers can change professor at Clemson University, in color thanks to the addition of South Carolina. “These properties, N O NO2 spiropyran molecules that undergo coupled with the fact that the color electrocyclic ring-opening in rechange can be maintained with the CH3 O sponse to mechanical force. The recessation of stress, can be exploited Spiropyran sulting ring-opened merocyanine by engineers in the design of polyPolymer molecules are brightly colored, meric components that visually producing red or purple hues in the indicate to the end-user their stress, polymer, depending upon how the strain, thermal, or ultraviolet-visiNO 2 Polymer indicator molecule is covalently ble light exposure history. It’s a true linked to the polymeric structure. smart material,” he says. O The spiropyran undergoes “a Sottos tells C&EN that the + –O N force-induced reaction inside of a work demonstrates the concept O solid structural polymer,” explains that mechanical force can trigger CH3 Polymer University of Illinois, Urbanathe activation of specific covalent Merocyanine Champaign, materials science bonds in a polymer. She hopes to professor Nancy R. Sottos, who develop new mechanophores that spearheaded the research. “It’s do more than just change color. RECKONING WITH FORCE a selective covalent bond cleavFor example, molecules that crossA colorless spiropyran age that occurs long before there link or polymerize in response to mechanophore undergoes is any backbone cleavage” of the mechanical stress could lead to electrocyclic ring opening to polymer itself, she adds. Forceself-toughening or self-healing produce a colored merocyanine sensitive molecules, known as materials, she says.—BETHANY in response to mechanical force. mechanophores, have been added HALFORD
P
Embedded mechanophores turn a rubbery polymer red just before it fails.
BIOTECHNOLOGY New report sees dry capital markets shrinking the sector Although the global biotechnology industry fared well in 2008, the recession is likely to spark consolidation in the year ahead as traditional sources of public funding go into long-term decline. Thus states Ernst & Young’s annual report on the industry. The consulting firm found that revenues of publicly traded biotech firms grew 12% to $90 billion in 2008. The global industry’s net loss shrank from $3.0 billion in 2007 to $1.4 billion last year, and the U.S. industry reached aggregate profitability for the first time.
Capital raised by publicly traded firms in the U.S. and Europe declined by 46%, however, to $16 billion in 2008. Funding for initial public offerings fell 95% to $116 million; other forms of public funding also dropped off almost entirely. Venture capital funding, on the other hand, remained relatively strong last year, falling only 19% from 2007’s all-time record of $6 billion. Glen T. Giovannetti, who coauthored the report, says Ernst & Young uncovered a spike in the number of companies that
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have less than a year’s worth of capital on hand. This is a concern, he says, given the difficulty these firms will now have in raising capital through the usual venues. The annual report has consistently found 20–25% of public biotech companies with less than a year’s worth of capital on hand, but Ernst & Young counted 44% of them in this position in 2008. Giovannetti estimates that that number has since risen to more than 50% and that the sector could shrink by as much as a quarter during the downturn.—RICK MULLIN
D. STEVEN SON , A. JER EZ, A. HAM ILTON & D. DAVIS
NEWS OF THE WEEK
