Surface Wettability Controllable Polyimides Bearing Long-chain Alkyl Groups by UV Light Irradiation

Abstract

The novel aromatic diamine monomer, 4-(3,5-diaminobenzoyl)phenyl 3,4,5-tris(decyloxy)benzoate (3C₁₀-PEBPDA) having three long-chain alkyl groups connected by phenylester and benzophenone linkages was synthesized via six step reactions from gallic acid methyl ester. The novel polyimides and copolyimides were synthesized from 3,4'-oxydiphthalic anhydride (3,4'-ODPA) as a dianhydride, 3C₁₀-PEBPDA, and 4,4'-diaminodiphenylether (DDE) as a diamine co-monomer by two step polymerization systems. The thin films of obtained polyimides were irradiated by UV light (λmax; 254 nm), and the contact angles for the water decreased from near 100^o (hydrophobicity) to near 50^o (hydrophilicity) in proportion to irradiated UV light energy. Furthermore, it was observed that the incorporation ratios of 3C₁₀-PEBPDA in copolyimides affected the changes of surface wettability by UV light irradiation. From the result of various analytical experiments, it is recognized that the hydrophobic long-chain alkyl groups on the polyimide surface decrease and the hydrophilic groups such as hydroxyl groups and carboxyl groups generate on their surface, and that oxygen in an air affect the generation of these hydrophilic groups.