| Abstract
| - Three functionalized second-order nonlinear optical polyimides were synthesized by thestep growth polymerization reaction between a chromophore-containing dianhydride andthree different diamine compounds. This alternate approach (i.e., incorporating a nonlinearchromophore into a dianhydride monomer) may avoid troublesome syntheses of thechromophore-containing diamine and can provide easy preparation of the polyimides withvarious chromophores. The number-average molecular weights (Mn) of final polymersdetermined by GPC ranged between 10 000 and 16 800 (Mw/Mn = 1.59−2.28). No meltingwas detected and they showed relatively low glass-transition temperatures ranging from161 to 181 °C. They are readily soluble in aprotic polar solvents such as tetrahydrofuran,N,N-dimethylformamide, N-methylpyrrolidinone, and so forth. High optical quality filmswere prepared by spin casting from a 10 wt % cyclohexanone or N-methylpyrrolidinonesolution. The second harmonic generation (SHG) coefficients, d33, of the polymers weredetermined to be 24−37 pm/V (d33(∞) = 7−10 pm/V) at a fundamental wavelength of 1064nm. All of the poled polymer samples showed outstanding orientational stability up to 125°C without any measurable decay of the SHG signal. In particular, the polyimide with a4,4‘-(hexafluoroisopropylidene)dianiline unit (PI-2-DANS) showed the best dynamical thermalstability of the poling-induced dipole alignment up to ca. 170 °C.
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