Mechanical force stimulates polymer growth

To date, most examples of polymer mechanochemistry—in which mechanical force initiates a chemical reaction—have involved breaking covalent bonds. But chemists working in this field would also like to use mechanical force to build bonds, just as the body uses mechanical force to restructure and reinforce bone. Taking a step in this direction, chemists at the University of California, Irvine, have developed a mechanically controlled radical polymerization process (Nat. Chem. 2016, DOI: 10.1038/nchem.2633). Aaron P. Esser-Kahn, Hemakesh Mohapatra, and Maya Kleiman used ultrasound to agitate piezoelectric BaTiO₃ nanoparticles, generating a potential that then reduced a copper(II) complex. The reduced copper(I) complex then reacted with an atom-transfer radical polymerization initiator, ethyl α-bromoisobutyrate, to stimulate polymerization of n-butyl acrylate monomer. The longer the team used ultrasound, the longer the polymer chains grew. Now the chemists are gearing up to use environmental vibrations to spur polymerization reactions.