Hexafluoroisobutylene and its higher homologs are easily reacted with SO.sub.3 to give fluorosulfates of the formula CH.sub.2.dbd.C(R)CF.sub.2OSO.sub.2F, wherein R is a linear branched or cyclic fluoroalkyl group comprised of 1 to 10 carbon atoms and may contain ether oxygen. These compounds react under mild conditions with many nucleophiles to give CH.sub.2.dbd.C(R)CF.sub.2X, where X is derived from the nucleophile. This reaction provides a route to many substituted hexafluoroisobutylenes, which copolymerize easily with other fluoro- and hydrocarbon monomers such as vinylidene fluoride and ethylene.