How can the degree of branching influence the lyotropic properties of amphiphilic block copolymers? In order to provide a qualitative answer to this question, we have prepared a library of poly(propylene sulfide)-bl-poly(ethylene glycol) (PPS-PEG) block copolymers, varying the hydrophobic block (PPS) length and its branching degree and thus producing diblock, triblock (that can be seen as two-armed star), tri-armed star and tetra-armed star structures. The PEG block, on the contrary, was kept constant (linear PEG2000). Although all the polymers exhibited a qualitatively similar lyotropic behaviour, an increased degree of branching of the hydrophobic block caused clear differences in the rheology of lyotropic phases, with an increasingly softer character, and in the organisation of the PEG chains, which appeared to adopt possibly more extended and dehydrated conformations. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved