Synthesis and optical nonlinearity of thermally stable polyimides incorporated with electro-optic chromophore as side chain

We prepared thermally durable nonlinear optical (NLO) polymers, based on a polyimide attached with a NLO chromophore as a side-chain. The polyimide with two aromatic hydroxyls in the repeat unit was prepared by condensation polymerization between 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane and oxydiphthalic anhydride in DMAc, followed by imidization reaction. Mitsunobu coupling was carried out to incorporate the NLO chromophore into the polyimide backbone, to yield the side-chain polymer with a loading level of the chromophore up to 65 wt%. The thermal characterization of the polymer showed that the NLO polyimide had T_g at 168°C and was thermally stable up to 370°C. The polymer solution was spin coated on the ITO glass to produce an optical quality film. The electro-optic coefficient of the film was obtained using 1.55 μm laser source, giving 31 pm/V with an electrical poling field of 1 MV/cm. The temporal stability of the polymer was confirmed over 330 h at 85°C under nitrogen condition.