A new method to synthesize a variety of well-controlled polylactide (PLA)-based block copolymers having disulfide linkages at block junctions (PLA-ss-PATRPs) was investigated. The method uses a combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP) that initiates the synthesis of a new disulfide-labeled double-head initiator having both terminal OH and Br groups (HO-ss-iBuBr). The amount of tin catalyst and polymerization time significantly influenced the control of ROP initiated with HO-ss-iBuBr. A series of ATRP of various methacrylates as well as acrylate and styrene in the presence of the resulting PLA-ss-iBuBr macroinitiators proceeded in a living manner. These well-controlled PLA-ss-PATRPs were further characterized for thermal properties using differential scanning calorimetry and thiol-responsive degradation upon the cleavage of disulfide linkages. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym. Chem. 2013, 51, 3071-3080