The d (FEU) value was calculated from d (PFPE)= 12Y13 MPa0.5[12] and d (urethane)=20Y21 MPa0.5, but the application of Eq. 4 to a segmented, phase segregated copolymer is admittedly a rough approximation. It could be noticed that in M15 the volume fraction of polar solvent (methanol, 15%) is similar to the volume fraction of polar