Solution properties of carboxylated polyurethanes (CPUs) and related ionomers (PUIs) in N,N-dimethylformamide (DMF) and DMF with added LiBr of different concentrations were investigated by size exclusion chromatography (SEC), viscometry and in the case of CPUs also by SEC coupled with a multi-angle light scattering detector (SEC-MALS). In DMF, both kinds of PUs have multimodal molar mass distributions, while the reduced viscosity-concentration profiles indicate an upturn in very dilute regions usually related to the polyelectrolyte effect. However, SEC-MALS measurements of non-carboxylated PU (NPU) and CPUs indicate that these PUs aggregate in DMF. After the addition of LiBr to DMF unimodal molar mass distributions with much larger elution volumes (V-c) and linear concentration dependences of reduced viscosity are obtained for both kinds of PUs. LiBr in DMF not only screens the ionic groups of carboxylated PUIs but also specifically interacts with the polar groups of PUs. Thus, LiBr suppresses any electrostatic and/or molecular interactions and consequently eliminates all the peculiarities encountered in SEC characterization of both kinds of PUs in DMF. (C) 2000 Elsevier Science Ltd, All rights reserved.