In these days, we are investigating about the functions of side chain crystalline block co-polymer (SCCBC). The side chain crystalline unit (SCCU) of SCCBC shows very strong adhesive force to polyethylene (PE) crystalline surface. The origin of this force is van der Walls interaction. And the SCCU and PE are thought to be forming pseudo crystal. So, we can call this interaction as “Crystalline Supramolecular Interaction”. By using this interaction, we can modify the surface properties of PE to any by choosing the other side of the block copolymer. We can also modify the inner surface properties of micro porous PE membrane. The hydrophilic modified membrane shows good separator function and also solid electrolyte membrane properties of Li ion secondary battery. Recently, we found that by using a monomer that has a tetrafluoroethylene structure side chain, we can modify the surface property of polytetrafluoroethylene to hydrophilic. In this time, we will discuss the mechanism of this Crystalline Supramolecular Interaction.