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Novel nonlinear optical (NLO) network polyurethane of lysine triisocyanate (LTI) with 44N-(2-hydroxyethyl)-N-methylaminol-3'-(hydroxymethyl)azobenzene (AZODIOL) dye as a NLO-phore has been prepared for second harmonic generation (SHG). A soluble prepolymer of LTI with AZODIOL was prepared, and then a thin prepolymer film was spun-cast on an indium tin oxide coated glass substrate. Two types of poling were carried out. One-step poling process: while high voltage between 5.0 and 8.0 kV was applied to the corona wire, the sample film was heated up and held at a temperature range of 70-190 "C for 10 min and then cooled down to room temperature for 40 min. Two-step poling process: while high voltage was applied to the corona wire, the sample was heated up and held at 90 "C for 1 h and then heated up again and held at a temperature range of 90-190 "C for 30 min. Then the sample was cooled down to room temperature while applying the poling field. The effects of the above poling condition and storage time and thermal annealing on SHG activity are investigated in connection with polymer structure. Better long-term thermal stability of SHG at room temperature can be obtained for the sample prepared by a two-step poling process. This better thermal stability is interpreted to be due to the smaller free volume for that sample.

This paper presents a novel class of nonlinear optical (NLO) polymer for second harmonic generation (SHG). This new class of NLO polymer consists of the linear polyurethane, T-polymer, of tolylene 2,4-diisocyanate (TDI) with 3-[(2-hydroxyethyl)amino]-5-(hydroxymethyl)-4‘-nitroazobenzene (T-AZODIOL), whose dipole moment is aligned transverse to the main chain backbone. For comparison, the linear polyurethane L-polymer, whose NLO chromophore is incorporated into the main chain, is synthesized from TDI with 4-[N-(2-hydroxyethyl)-N-methylamino]-3‘-(hydroxymethyl)azobenzene (AZODIOL). T-polymer poled at optimum conditions of a corona poling voltage 8.0 kV, a temperature of 95 °C, and a time of 60 min shows a large second-order nonlinearity of d 33 = 1.6 × 10-7 esu (67 pm/V) with good thermal stability at room temperature. The oriented NLO dipole moments for T-polymer do not show significant relaxation at ambient conditions after 60 days except for small depression a few days after poling, whereas, the SHG activity of L-polymer is largely decayed at room temperature. The better thermal stability of this new class of T-polymer is related to the smaller free volume in T-polymer.

This paper presents the internal electric field created by the preferentially oriented /3-crystallite dipoles in the blends of 75 mol % vinylidene fluoride-25 mol % trifluoroethylene copolymer (P(VDF-TrFE)) and poly(methyl methacrylate) (PMMA) and the second harmonic generation (SHG) from the oriented /3-crystallite dipoles and that from the nonlinear optical (NLO) dyes noncentrosymmetrically aligned by the internal electric field. We have also prepared the copolymer of methyl methacrylate (MMA) with a vinyl monomer having a NLO pendant amino-nitro-azobenzene (P(MMA-co-MMA-DRl)) as a SHG active polymer. The blends of both P(VDF-TrFE)/PMMA and P(VDF-TrFE)/P(MMA-co-MMA-DRl) with lowDRl content (experimentally up to 4 mol %) show optical clarity that is desirable for SHG materials. Internal electric fields (Ei) of 1.7-3.2 MV/cm, which is significantly larger than the applied field of 0.8 MV/cm, were measured at the P(VDF-TrFE) content above 70 mol %. SHG coefficient <¿33 values are 3.3 X *9,2.3 x 10~9, and 0.9 X10-9 esu for P(VDF-TrFE), (90/10) P(VDF-TrFE)/PMMA, and (90/10) P(VDF-TrFE)/P(MMA-co-MMA-DR1), respectively. Temperature profiles of E¡ for the blends are shared by those of pyroelectricity and those of ¿33. Their activities are not significantly depressed at the glass transition temperature T, but are drastically lost at the temperature around the Curie transition temperature, which is higher than Tg. We will discuss the nature of the thermal stability of the internal electric field, pyroelectricity, and SHG activity, relating to the order-disorder transition of /3-crystallite dipoles at the Curie transition temperature.

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