Photoinduced optical anisotropy in new poly(amide imide)s with azobenzene units

Two series of new photosensitive poly(amide imide)s (PAIs) containing photochromic azobenzene moieties as side groups have been synthesized. For this purpose the following diamines with azobenzene groups have been prepared: 2,4-diamino-4′-fluoroazobenzene, 2,4-diamino-4′-methylazobenzene, 2,4-diamino-4′-trifluoromethoxy-azobenzene and 2,4-diamino-4′-nitroazobenzene. The poly(amide imide)s have been obtained from diamidedianhydrides and diamino-chromophores using high-temperature polycondensation. The resulting polyimides are characterized by good solubility in some solvents, high glass transition temperatures (257-280 °C), high thermal decomposition temperatures and good film forming properties. The irradiation with linearly polarized light (488 nm, 100 mW/cm2), causes a reorientation of the azobenzene groups by angular-selective EZ photoisomerization. In this way optical anisotropy is induced in the initially isotropic films casting from the amorphous polymers. The photoinduced dichroism in the films has been measured, and the results are discussed in relation to the structure of these polymers, whereas the substitution of the azobenzene moiety and the structure of the backbone are varied.