Synthesis and Properties of a Second-Order Nonlinear Optical Side-Chain Polyimide YOSHIMASA SAKAI, 1 MITSURU UEDA, 1 TAKASHI FUKUDA, 2 HIRO MATSUDA 2 1 Department of Human Sensing and Functional Sensor Engineering, Graduate School of Engineering, Yamagata University, Yonezawa, Yamagata 992-8510, Japan 2 National Institute of Materials and Chemical Research, 1-1 Higashi, Tsukuba, Ibaraki, 305-0046 Japan Received 26 June 1998; accepted 7 September 1998 ABSTRACT: A thermal stable aromatic polyimide (PI) with side-chain second-order nonlinear optical (NLO) chromophores has been developed. The PI was prepared by the ring-opening polyaddition of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride with a new diamine having two N-ethyl-N-[4-[(6-chlorobenzothiazol-2-yl)diazenyl]phenyl]-2- aminoethanol units as the NLO chromophore, followed by poling during or after the thermal imidization process. The resulting PI had number and weight-average molec- ular weights ( M n , M w ) of 25,000 and 80,000, respectively, and a relatively high glass transition temperature of 180°C. The second harmonic coefficient ( d 33 ) of PI at the wavelength of 1.064 m was 138 pm/V (329.6  10 -9 esu) and remained unchanged at elevated temperatures. The corona poling process of the NLO-substituted poly(amic acid) to the PI was also studied in detail by measuring the second harmonic generation (SHG) from the polymer films. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1321–1329, 1999 Keywords: second-order nonlinear optical polyimide; second harmonic coefficient; corona poling INTRODUCTION Second-order nonlinear optical (NLO) materials are currently of interest to a large number of research groups as they have potential applica- tions in areas such as telecommunications, optical information processing, and data storage. 1–3 Many reports have been published on the devel- opment of polymers with NLO chromophores. These polymers are prepared either by radical polymerization or by step growth polymerization of monomers containing chromophores. One of the major difficulties with these materials is the long term relaxation of the NLO chromophores back into the isotropic state. Therefore, recent research efforts have been focused on enhancing the stability of dipole orientation at elevated tem- peratures. 4–6 Among various polymers, aromatic polyimides have been selected as promising can- didates to overcome the above problem because their higher glass transition temperatures are ef- fective in restraining the relaxation of the NLO- chromophore alignment induced by an electric field. The NLO polyimides exhibiting high orienta- tion stability were prepared by using diamines containing NLO chromophores 7,8 and through the introduction of chromophores to poly(hydroxy– imide)s. 9 –12 The magnitude of the macroscopic nonlinear effect is determined by the number den- sity of chromophores within the polymers. Thus, the former approach should be reliable for the introduction of chromophores in every repeating unit. Correspondence to: M. Ueda Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 37, 1321–1329 (1999) © 1999 John Wiley & Sons, Inc. CCC 0887-624X/99/091321-09 1321