Graft copolymer production with minimal reactor coating

Graft copolymers are obtained by an aqueous- phase process in which polymerization of the rubber-elastic base is taken to completion and an N-oxyl radical compound of a sec. amine with no hydrogens on the alpha -carbon atom is added before and/or during polymerization of the grafted shell. A process for the production, in the aqueous phase, of graft copolymers (A) of (a1) 30-95 wt% rubber-elastic graft base derived from (a11) 50-100 wt% conjugated diene and (a12) 0-50 wt% other monounsaturated monomer(s) or from (a11 asterisk ) 50-100 wt% 1-10C alkyl acrylate, (a12 asterisk ) 0-10 wt% polyfunctional crosslinking monomer and (a13 asterisk ) 0-40 wt% other monounsaturated monomer(s) and (a2) 5-70 wt% grafted shell derived from (a21) 50-100 wt% styrene compound of formula (S): R , R = H or 1-8 C alkyl (a22) 0-40 wt% (meth)acrylonitrile and (a23) 0-40 wt% other monounsaturated monomer(s). In this process, polymerization of the base stage (a1) is taken to completion and then at least one N-oxyl radical compound of a sec. amine with no hydrogen atoms on the alpha -carbon atom is added before and/or during polymerization stage (a2). An Independent claim is also included for graft copolymers obtained by this process.