Two-step synthesis of side-chain aromatic polyimides for second-order nonlinear optics

A two-step, generally applicable synthetic approach for NLO side-chain aromatic polyimides was developed. This is a one-pot preparation of a preimidized, hydroxyl polyimide, followed by the covalent bonding of a chromophore onto the backbone of the polyimide via a mild post-Mitsunobu reaction. NLO side-chain aromatic polyimides with different polymer backbones and different chromophores were synthesized, and the chromophore loading level in the polyimides was controlled efficiently from 0 to 50% by weight. This facile method provides the synthesis of NLO polyimides with a broad variation of polymer backbone and side-chain chromophores to fine-tune the electrical and structural properties. All the synthesized NLO side-chain polyimides have high glass transition temperatures (T_g > 220 °C) and thermal stability. A large electro-optic (E-O) coefficient (r₃₃) value (11 pm/V measured at 0.83 μm and 34 pm/V at 0.63 μm) and long-term stability (>500 h at 100 °C) of the dipole alignment were observed.