Novel diamine monomers having hydrophobic groups were synthesized from natural products such as ferulic acid and γ-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 (λmax; 254 nm), and the contact angles for the water decreased from 90-100° (hydrophobicity) to minimum 35° (hydrophilicity) in proportion to irradiated UV light energy. The tendency in this wettability change is larger in the case of polyimides based on a γ-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.
The novel aromatic diamine monomer, 4-(3,5-diaminobenzoyl)phenyl 3,4,5-tris(decyloxy)benzoate (3C 10 -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, 3C 10 -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° (hydrophobicity) to near 50° (hydrophilicity) in proportion to irradiated UV light energy. Furthermore, it was observed that the incorporation ratios of 3C 10 -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.
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