Novel synthetic route of soluble polyimides and their second-order nonlinear optical properties

Abstract

Nonlinear optical (NLO)-functionalized polyimides were directly synthesized using a nitro-displacement reaction between an alkyldiol monomer and a diimide monomer without thermal curing step and complicating condition. The polyimides are soluble in aprotic polar solvents such as DMSO, DMAc, DMF and NMP and showed their glass transition to be between 172 and 198℃. The polyimides showed good thermal stability up to 300℃ (at 5% weight loss). The weight average molecular weights of the resulting polymers were determined to be 10400~15100 $(M_w/M_n = 1.84 \sim 2.00)$. The poled polymer films showed very high nonlinearity with second harmonic generation coefficient $d_{33}$ in the range of 54~76 pm/V in second harmonic generation (SHG) experiment using Maker Fringe method. Also, the non-resonant value, $d_{33}$ (∞) calculated with two-level model was 21 pm/V and 14 pm/V for PEI 1-DANS and PEI 2-DANS, respectively.