The bis-sulfonamide m-C6H4(SO2NHPh)(2) efficiently promotes the ring-opening polymerization of lactide when combined with tertiary amines, such as N,N-dimethylamino-pyridine. Polylacticles of controlled molecular weights (M-n up to 17,700 g mol(-1)) and very narrow molecular weight distributions (M-w/M-n < 1.11) are obtained under mild conditions and in a living fashion. The reaction takes place through a bifunctional mechanism involving activation of both the alcohol and the monomer. Modulation of the sulfonamide component supports cooperative dual hydrogen-bonding of lactide involving the two (SO2NHAr) moieties. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 959-965, 2010