The free radical polymerization of chloromethylstyrene (CMS) with benzoyl peroxide (BPO) as initiator and 2,2,6,6 tetramethyl-1-piperidiniloxy (Tempo) as counter radical was studied. The living character was demonstrated by the linear dependence of (M) over bar(n) versus conversion like that the control with polydispersity lower than 1,5. In a second step, styrene was introduced in polychloromethylstyrene capped with Tempo to produce PCMS-b-PS block copolymers (12,000/60,000) with and PCMS-Tempo macroinitiator efficiency closed to 85%.