Synthesis of photocrosslinkable non-linear optic polyimides and electro-optic properties

Photocrosslinkable polyimide-type non-linear optical (NLO) polymers were obtained by multi-step reactions. Polyimide substrate polymer (P05) made From 3,3'-diamino-4,4'-dihydroxybiphenyl (HAB) and aromatic dianhydride (6FDA) had higher molecular weight than other polyimides due to the high nucleophilicity of the amine group in HAB compared to the one in 2,2'-bis(3-amino-4-hydroxyphenyl)hexafluoropropane(Biri-AP-AF) with the electron-withdrawing group. The introduction of DR-1 chromophore into the polyimide substrate polymers depended on the steric factor between the bulky DR-1 chromophore and the substrate polyimide in the polymer reaction via the Mitsunobu reaction. In the DR-1 substituted NLO polyimides, Tg decreased with the increasing amount of DR-1 chromophore. Photocrosslinkable NLO polyimide (P05-DR-cin) was obtained by the introduction of the photoreactive cinnamoyl group into the DR-1 substituted polyimides. The electro-optic coefficient (r(33)) Of the NLO polymer was determined with an experimental set-up capable of real-time measurement by varying both the poling field and temperature. The electro-optic coefficient (r(33)) of the linear NLO polymer (P05-DR) started to show a decrease of the r(33) value from about 80 degreesC. The photocrosslinked NLO polymer (P05-DR-cin). however, maintained a high r(33) value up to 150 degreesC due to chromophores locked in the polymer matrix with a network structure.