Yusuke Tsuda

The novel polyimides containing perfluoroalkyl group on their side chain were synthesized using the novel diamine monomers containing perfluoroalkyl group. The films of obtained polyimides on glass substrates were prepared and the surface wettability of these films were measured before and after UV (ultraviolet) light irradiation (254 nm). The water contact angles of these polyimide films were changed from about 113° to 56° by UV light irradiation. The novel polyimides containing both perfluoroalkyl group and spiropyran group was synthesized by introducing spiropyran group by Mitsunobu reaction with base polyimide containing phenolic OH group. The surface wettability of the polyimide film containing the spiropyran group changes from about 114° to about 104° by irradiation of UV light (365 nm), and reversibly changes from about 104° to about 114° by irradiation of Vis (visible) light.

The novel polyimides having trifluoromethyl groups were synthesized and the introduction of spiropyran groups on their side chain by Mitsunobu reaction were succeeded. The films of obtained polyimides on glass substrates were prepared and the surface wettability of these films were measured before and after UV/VIS light irradiation. As a result, the initial contact angles of the novel spiropyran-containing fluorinated polyimides improved by up to 40°. As expected, the contact angle decreased by UV light irradiation and recovered by VIS light irradiation. However, the change in contact angle was about 10°, which was the same values as the result previously reported.

The soluble polyimides were synthesized from tetracarboxylic dianhydrides such as 3,4'-oxydiphthalic anhydride (3,4’-ODPA) and diamine monomers having various photoreactive groups, which are photo-oxidative groups, photoreaction groups based on photoresist technology, and photochromic groups. The thin films of obtained polyimides were irradiated by UV light (λ max; 254 nm or 365 nm), and the contact angles for the water decreased from near 100° (hydrophobicity) to minimum 20° (hydrophilicity) in proportion to irradiated UV light energy. The reversible wettability changes of the polyimides having photochromic groups by UV-Vis light irradiation were also investigated. Various surface analysis such as ATR, solid state refractive UV, XPS support above surface wettability changes of the polyimides.

The novel polyimide having spiropyran groups on their side chain was synthesized, and the thin films of the polyimide on glass substrates were prepared. It was confirmed that the surface wettability of these films were changed from around 76° to around 67° by UV (365 nm) light irradiation, and the surface wettability were reversibly changed from 67° to 76° by Vis (visible) light irradiation. These wettability changes were photo-cyclized three times. The UV-Vis spectroscopy analysis indicates that the photo-induced isomerization of the spiropyran group leads to reversible changes on the surface of the polyimide films.

The novel polyimides and copolyimides are synthesized from the diamines having three long-chain alkyl groups connected by phenyl ester linkages, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride or diphenylsulfonetetracarboxylic dianhydride as a tetracarboxylic dianhydride, and 4,4’-diaminodiphenylether as a diamine comonomer. These polyimides show good film-forming ability and good thermal properties. The thin films of obtained polyimides were irradiated by ultraviolet (UV) light ( λ_max = 254 nm), and the contact angles for the water decreased from near 100° (hydrophobicity) to near 20° (hydrophilicity) in proportion to irradiated UV light energy. From the result of attenuated total reflectance analysis, it is recognized that the hydrophobic long-chain alkyl groups on the polyimide surface decrease and the hydrophilic groups such as carboxyl groups and hydroxyl groups generate on their surface. Thus, the surface wettability of these polyimides can be controlled by UV light irradiation, and this method is expected to be applied in the field of printed electronics.

Polyimides having dendritic side chains were investigated. The terphenylene diamine monomer having a first-generation monodendron, 3,4,5-tris(n-dodecyloxy)-benzoate and the monomer having a second-generation monodendron, 3,4,5-tris[-3’,4’,5’-tri(n-dodecyloxy)benzyloxy]benzoate were successfully synthesized and the corresponding soluble dendritic polyimides were obtained by polycondensation with conventional tetracarboxylic dianhydride monomers such as benzophenone tertracarboxylic dianhydride (BTDA). The two-step polymerizations in NMP that is a general method for the synthesis of soluble polyimides is difficult; however, the expected dendritic polyimides can be obtained in aromatic polar solvents such as m-cresol and pyridine. The solubility of these dendoronized polyimides is characteristic; soluble in common organic solvents such as dichloromethane, chloroform, toluene and THF. These dendronized polyimides exhibited high glass transition temperatures and good thermal stability in both air and under nitrogen. Their application as alignment layers for LCDs was investigated, and it was found that these polyimides having dendritic side chains were applicable for the vertically aligned nematic liquid crystal displays (VAN-LCDs).