Well-defined poly(methyl methacrylate) (PMMA) with very low polydispersity and with α-Et₂NCS₂ and ω-Cl end groups was synthesized ia in situ atom transfer radical polymerization (ATRP), using a tetraethylthiuram disulfide (TD)–FeCl₃–PPh₃ initiating system. The in situ ATRP of methyl methacrylate (MMA) was a “living”/controlled polymerization and the polydispersity indices of PMMA were very narrow (M_n = 7100 and M_w/M_n = 1.04). The presence of the Et₂NCS₂ and the chlorine atoms as end groups in PMMA was determined by ¹H NMR, FT-IR and UV spectroscopies. The presence of an ω-chlorine end group on the polymer chain was used to chain extend the PMMA using a conventional ATRP initiation system.