Neoprene

Natural rubber swells and softens in oil and cracks in sunlight. In April 1930 Arnold Collins, working in Wallace Carothers' group at DuPont, isolated chloroprene - a close relative of the isoprene in natural rubber, with one chlorine atom in place of a methyl group - and found that it polymerised by itself into a rubber-like solid. DuPont sold it from 1931 as DuPrene and renamed it neoprene in 1937. It was one of the first commercially successful synthetic rubbers, and its selling point was exactly what natural rubber lacked: resistance to oil, weather and heat. **No patent number is cited here**: the chemistry is well documented and dated, but no single patent was verified as covering neoprene itself, so none is claimed. **You make a snug neoprene sleeve with a glued-and-stitched butt seam, then test the claim** - a strip of neoprene and a natural rubber band in mineral oil for a day, measured before and after.