Thermally stable second-order nonlinear optical addition-type polyimides functionalized by diamine chromophore

A series of chromophore-functionalized polyimide prepolymers with excellent processibility were prepared by a Michael addition reaction of diamine chromophore 2 with structurally different bismaleimide (BMI) monomers. The effects of the BMI moiety's structure and thermal curing condition on glass transition temperature (T_g) and thermal stability of the polyimides were studied by DSC, TGA, and FTIR. Among the five cured polyimides, PI₃, bearing a sulfone moiety, exhibited the highest T_g and thermal decomposition temperature (T_d). Its corresponding prepolymer, PP₃, was selected to evaluate NLO properties in a simultaneously poling and thermal polymerization process. A relatively large poling-order parameter was observed. The second-order nonlinear coefficient, d₃₃, was 25 pm/V at 1064 nm fundamental wavelength. The second harmonic generation signal was almost without decay up to 170 °C.