Elastic-thermoplastic graft polymers manufactured by radical emulsion polymerization of resin-forming vinyl monomers in the presence of rubber present in latex form with the use of a combination of a peroxide of formula (I) ##STR1## where R.sup.1 signifies alkyl, cycloalkyl and aryl groups with 4 to 20 carbon atoms, X the groups --COOH and --SO.sub.3 H as well as their alkali, alkaline-earth or ammonium salts, n an integer in the range from 1 to 6, A alkylene, cycloalkylene and arylene groups with 6 to 40 carbon atoms and a reducing agent as initiator system, a method for their manufacture and their use as moulding compositions.