Ring-opening metathesis polymerization (ROMP) is typically a transition metal activated polymerization method using cyclic olefins, which are joined together to form a polymer chain. However, metal byproducts lead to complications with measurements using electronic or optical properties. Residual metallic species also compromise biological studies and lead to unwanted oxidative processes.

Andrew J. Boydston and colleagues at the University of Washington, Seattle, USA, have developed a transition-metal free alternative to ROMP that uses a one-electron oxidation of a vinyl-ether initiator. The direct oxidation of the vinyl ether generates a radical cation, which reacts with a cycloalkene monomer giving a [2+2] complex. The complex rapidly ring-opens to alleviate ring strain, and propagation with additional monomers yields ROMP polymers.

The researchers investigated the propensity of vinyl ethers to activate ROMP both electrochemically and via photoredox initiation using a norbornene monomer. Photo-oxidation gives high yields of polymer under mild conditions as well as temporal control over reinitiation of polymer growth during on/off cycles of blue LED light.

• Metal-Free Ring-Opening Metathesis Polymerization,
  K. Ogawa, A. Goetz, A. Boydston,
  J. Am. Chem. Soc. 2015, 137, 1400–1403.
  DOI: 10.1021/ja512073m