Polymers with chemically labile disulfide groups in the backbone were prepared by atom transfer radical polymerization (ATRP) of styrene using the 2-bromopropionic acid diester of bis(2-hydroxyethyl) disulfide as the initiator and CuBr/N,N,N',N'',N''-pentamethyldiethylenetriamine as the catalyst at 90 degreesC. Polymerization kinetics indicated insignificant transfer to the disulfide originating from the initiator. Using a monomer-to-initiator-to-catalyst ratio of 300:1:0.2, radical coupling reactions were suppressed compared to systems with more catalyst (300:1:1), and well-defined (with symmetrical and narrow (M-w/M-n < 1.1) molecular weight distribution) disulfide-containing polymers were prepared. The internal disulfide bond was cleaved by reduction with dithiothreitol to yield the corresponding thiol-terminated polystyrene. The thiol end groups were efficiently coupled back to the starting disulfide by oxidation with FeCl3. A dibromo-terminated polystyrene was synthesized under similar ATRP conditions using dimethyl 2,6-dibromoheptanedioate as the initiator and was used as a precursor for dithiol-terminated polymer. Thiodimethylformamide was employed to convert the bromine end groups to thiol functionalities. The obtained difunctional polymer was coupled to a high molecular weight product with internal disulfide bridges upon oxidation with FeCl3.