In one or more embodiments, the present invention provides an way to modify the isoprene unit using an alder-ene reaction to form thermoset compounds comprising the resultant electron-deficient, readily crosslinkable polyisobutylene-based rubber that avoids the use of corrosive bromine or chlorine to make the activated butyl rubber, is easier to crosslink than the halobutyls, allows crosslinking with a simple organic base or a peroxide, and has mechanical properties as good as or better than sulfur crosslinked butyl rubbers.