In this study, the preparation of a new class of amphiphilic block copolymers consisting of a poly(phthalaldehyde) (PPA) block and hydrophilic poly(alkylene oxide) blocks is described. PPA was prepared by ionic cyclopolymerization. A telechelic polymer block was prepared by endcapping of the PPA by a bifunctional reagent carrying isocyanate and isothiocyanate groups. As the second block, monoamino-terminated poly(alkylene oxide)s (Surfonamines (R), also known as Jeffaminese (R)) were chosen. These polymers could be readily coupled to the PPA telechel and gave amphiphlic, mainly ABA-type block copolymers. The PPA block of these products can be selectively depolymerized at moderate temperature. The block copolymers were characterized by dual-detection size exclusion chromatography, and the defined and stepwise thermal decomposition of the two different block types were shown by thermogravimetric analysis. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1499-1509,2009