Synthesis and properties of a second-order nonlinear optical side-chain polyimide

A thermal stable aromatic polyimide (PT) 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 PT had number and weight-average molecular weights (M(n), M(w)) of 25,000 and 80,000, respectively, and a relatively high glass transition temperature of 180 degrees C. The second harmonic coefficient (d(33)) of PI at the wavelength of 1.064 mu m was 138 pmN (329.6 x 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. (C) 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1321-1329, 1999.