Butyl Rubber

Polyisobutylene was a soft, sticky material that could not be vulcanised - it had no double bonds left for sulphur to bridge. At Standard Oil in 1937 William Sparks and Robert Thomas added a few percent of isoprene to the isobutylene, just enough double bonds to cure it, and polymerised the mix far below freezing. The result held air better than any rubber before it, and inner tubes have been made of it ever since. **US 2,356,128**, "Mixed olefinic polymerization process and product", Thomas and Sparks, assigned to Jasco, filed 20. October 1939, granted 22. August 1944: an isoolefin with a small amount of diolefin, polymerised below 0 °C (down to about -160 °C) with aluminium chloride; it describes "a low, controlled, chemical unsaturation, capable of being cured with sulfur". **You measure the two properties that made its name**: it barely bounces, and it barely leaks.