Surface Wettability Controllable Polyimides Having Natural Product Skeletons by UV Light Irradiation

Novel diamine monomers having hydrophobic groups were synthesized from natural products such as ferulic acid and gamma-oryzanol. The novel polyimides and copolyimides were synthesized from 3,4'-ODPA as a dianhydride, above diamines having natural product skeleton, and DDE as a diamine co-monomer by two step polymerization systems. The thin films of obtained polyimides were irradiated by UV light (lambda max; 254 nm), and the contact angles for the water decreased from 90- 100 degrees (hydrophobicity) to minimum 35 degrees (hydrophilicity) in proportion to irradiated UV light energy. The tendency in this wettability change is larger in the case of polyimides based on a gamma-Oryzanol skeleton than in the case of polyimides based on a Ferulic acid skeleton. From the result of surface analyses (ATR, XPS, AFM), it is recognized that the hydrophobic alkyl groups on the polyimide surface decrease and the hydrophilic groups such as hydroxyl groups and carboxyl groups generate on their surface.