Atom-transfer radical polymerization, or ATRP, is a popular method for making polymers used as adhesives and coatings. The technique polymerizes styrenes, acrylates, methacrylates, acrylonitrile, acrylamides, and other vinyl monomers to produce polymers with uniform chains. The polymerization has one problem though: It requires a metal catalyst, such as copper, ruthenium, or iron, which can contaminate the polymer. Now, chemists at Dow Chemical; the University of California, Santa Barbara; and Cornell University have found a way to eliminate the metal from this transformation. The team, led by UCSB’s Craig J. Hawker and Cornell’s Brett P. Fors, uses an organic catalyst, 10-phenylphenothiazine, and light to initiate the polymerization (J. Am. Chem. Soc. 2014, DOI: 10.1021/ja510389m). In addition to being metal-free, the polymerization process can be controlled by switching the light on or off. “Having a green, organic ATRP process will open many new avenues for this field and also plays into the growing interest in photoredox systems in organic chemistry,” Hawker says.