Di- and triblock copolymers of styrene and butyl acrylate with controlled molar masses ((M) over bar(n) up to approximate to 10(5)) were sequentially prepared by radical atom transfer polymerization in a homogeneous medium using chlorine end capped polymers,as initiators and the copper((I)) chloride/bipyridine complex as catalyst, in the presence of dimethylformamide. Random poly(styrene-co-butyl acrylate) was synthesized and the crossover reactions between Cl end capped polystyrene and poly(butyl acrylate) to the opposite monomers were examined.