Block copolymers of ethylene oxide (EO) and propylene oxide (PO) are characterized by liquid chromatography under critical conditions (LCCC) for EO on a Diol column in acetone water 78:12 (w/w) and for PO, on a poly(divinyl benzene) column in acetone water 92:8 (w/w) or on a silica based poly(ethylene glycol) phase in 45:55 (w/w). Under these conditions, the other (non-critical) block elutes in exclusion mode, which allows an independent determination of the molar mass distribution of the individual blocks. These systems allow also the identification of homopolymers. The results thus obtained are compared to those from size exclusion chromatography (SEC) with coupled density and refractive index (RI) detection, which allows the determination of the entire MMD and the chemical composition along the MMD. (c) 2005 Elsevier Ltd. All rights reserved,