Molecules of low molecular weight have a different effect on the interface compared with polymers.Surface is less sensitive to changes in the solution when liquid-solid interface is analyzed.However, properties associated with nature of chain could be strongly affected by its length.The objective of this work was study the effect of chain length on surface free energy when molecules with low molecular weight are grafted to porous membrane.This procedure produces a surface change in order to make a more hydrophobic surface without to change the functional properties of the membranes (permeability, porosity, thickness, etc.).The development of this type of modified membranes could permit the making of anti-biofouling surface by decrease of interaction between the surface and extracellular polymeric substances.Results evidence that interpenetrating polymer network (IPN) can be made using polypropylene membranes as support and poly(allyl alcohol) as secondary network.In addition, alcohols can be inserted by urethanization Polymer network Surface modificationUrethanization Grafting