Polymeric macromolecules of well-designed structures and specific properties open promising directions in the capillary entangled polymer electrophoresis. Pluronic F-127, as a thermoassociating polymer, possesses some unique properties that can be utilized in capillary entangled polymer electrophoresis of amino acids, peptides and proteins. In this study, we studied properties of Pluronic F-127 polymer as an additive to BGE for the separation of peptides and proteins. The influence of the thermoassociation on separation selectivity was studied. The addition of Pluronic caused severe instabilities of the electrical current and the signal of the UV detector. This study reveals remarkable positive effect of a low pressure applied to the inlet buffer vial during the analysis, which apparently stabilizes the electrical current and the detector signal. The effect of hydrodynamic flow induced by the pressure applied on the separation efficiency was studied and the significance of this effect was discussed. Pluronic F-127, as a representative of synthetic macromolecules, was compared with dextran, as a representative of natural polymers, in terms of separation power, selectivity and repeatability of migration times.