Atom transfer radical polymerization (ATRP) was successfully applied to the synthesis of styrene-acrylonitrile (SAN) copolymers of predetermined molecular weights and low polydispersities. The monomers were copolymerized under azeotropic conditions (ca. 63 mol % styrene and 37 mol % acrylonitrile) in bulk using mono- and difunctional alkyl halide initiators such as 2-bromopropionitrile, I-phenylethyl bromide, methyl 2-bromopropionate, poly(ethylene oxide) monomethyl ether 2-bromopropionate, and the bis(2-bromopropionate) esters derived from poly(ethylene oxide), poly(propylene oxide), or poly(epsilon-caprolactone) diols of various molecular weights in combination with two catalytic systems: CuBr/2,2'-bipyridine (bpy) and CuBr/N,N,N',N",N"-pentamethyldiethylenetriamine (PMDETA). The synthesized copolymers had high chain end-functionalities, as proven by further chain extension with styrene, n-butyl, tert-butyl, or glycidyl acrylate, and methyl methacrylate. In the last case, the reaction in the presence of CuBr/bpy led to a block copolymer of high polydispersity, which was decreased to M-w/M-n = 1.5 using halogen exchange (i.e., CuCl/bpy as the catalytic system). All other block copolymers (including di-, tri-, and pentablock copolymers) had narrow molecular weight distributions (M-w/M-n, 1.1-1.4).