(X = Et, Bu, Me(CH(2))(5) or Me, Y = Me, Me, Me or Me(CH(2))(7), resp.) were added to SiO(2)-filled methylvinylsilicone rubber (3 parts per 100 parts rubber) to accelerate its vulcanization with (PhMe(2)CO)(2). The vulcanization time was a reduced from 30 min down to 6 min. The rubber vulcanizates showed improved mech. properties but deteriorated degrdn. resistance during UV and heat ageing.