[en] Highlights: • Membrane permeability due to pluronic polymers was investigated by SH spectroscopy. • Permeability depends on the length of the hydrophobic segment present in the polymer. • Permeability increases by 9 times in presence of ∼0.3 molecule of F-127 per liposome. • Lipid mobility near the vicinity of the adsorbed polymer increases significantly. • Polymer-lipid interaction depends on bilayer rigidity and polymer hydrophobocity. Pluronic polymer induced transport of an organic cation across a negatively charged POPG membrane bilayer were studied using interfacial selective Second Harmonic (SH) spectroscopic technique. The length of either hydrophilic (poly-ethylene oxide) or hydrophobic (poly-propylene oxide) unit in the polymer was varied to investigate their effect on membrane transport. Membrane transport was observed to depend critically on the length of the hydrophobic segment present in the polymer. Membrane transport studies using polymers which were either ‘incorporated’ or ‘incubated’ with the lipid bilayer suggested that bilayer packing plays a critical role in the insertion of polymers having a long hydrophilic chain.