A process of making a sulfur-containing organosiloxane polymer, comprising reacting a polymerizable organosiloxane having the formula RI [-s't-o-J wherein R is a monovalent hydrocarbon radical, x is at least 3, and R is a member of the group consisting of vinyl and allyl radicals, with a mercaptan, said mercaptan being a member of the group consisting of alkyl mercaptan, mercapto alkanol and merca