In 1927, he found that when the olefin stilbene was added to an ethyl ether solution of phenylisopropyl potassium, an abrupt color change from red to yellow took place. He had just observed the first addition of an organoalkali metal compound across a carbon-carbon double bond. Further work showed that he could successively add more and more of the olefinic hydrocarbon butadiene to a solution of phenylisopropyl potassium and obtain a long-chain hydrocarbon with the reactive organopotassium end still intact. Oligomers such as these were the forerunners of the so-called "living polymers"