ydrocarbon radicals, R is a divalent alkylene radical of from 1 to 4 inclusive carbon atoms and x is 0, 1 or 2, any remaning siloxane units in the polyorganosiloxane having the formula ##STR7## wherein R' is as defined above and y is an integer from 0 to 3 inclusive, said polyorganosiloxane having a degree of functionality of from 2.2 to 5.0, and (b) an effective amount of a hydroperoxy initiator