NONLINEAR-OPTICAL POLYMERS .1. NOVEL NETWORK POLYURETHANE WITH AZOBENZENE DYE IN THE MAIN FRAME

Novel nonlinear optical (NLO) network polyurethane of lysine triisocya nate (LTI) with 4-[N- ethyl)-N-methylamino]-3'-(hydroxymethyl)azobenze ne (AZODIOL) dye as a NLO-phore has been prepared for second harmonic generation (SHG). A soluble prepolymer of LTI with AZODIOL was prepare d, and then a thin prepolymer film was spun-cast on an indium tin oxid e coated glass substrate. Two types of poling were carried out. One-st ep poling process: while high voltage between 5.0 and 8.0 kV was appli ed to the corona wire, the sample film was heated up and held at a tem perature range of 70-190 degrees C for 10 min and then cooled down to room temperature for 40 min. Two-step poling process: while high volta ge was applied to the corona wire, the sample was heated up and held a t 90 degrees C for 1 h and then heated up again and held at a temperat ure range of 90-190 degrees C for 30 min. Then the sample was cooled d own to room temperature while applying the poling field. The effects o f the above poling condition and storage time and thermal annealing on SHG activity are investigated in connection with polymer structure. B etter long-term thermal stability of SHG at room temperature can be ob tained for the sample prepared by a two-step poling process. This bett er thermal stability is interpreted to be due to the smaller free volu me for that sample.