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A novel class of NLO polyimide was obtained by modified a backbone polyimide, consisting of promellitic dianhydride (PMDA) and succinamide, with a functional based on biphenyl. The resulting polymer shows exceptional thermal stability higher than the polyimide skeleton. Moreover, high electro- optical activity of the corona poled polymeric film is determined, and the phase separation which usually occur in the side-chain system is effectively minimized. Successful reactions were confirmed by 1H NMR and FT-IR spectra and the weight of the polymer was determined by gel permeation chromatography analysis. From DSC and TGA thermograms the glass transition temperatures up to 320 degree(s)C and initial decomposition temperature up to 480 degree(s)C. The polymer solution in DMF could be spin coated on the indium-tin-oxide (ITO) glass or other substrates to form optical quality thin films. In our experiments the in situ poling and temperature ramping technique was used to select the optimal temperature (Topt) in order to get the largest second-order NLO response. The electro-optic coefficient ((gamma) 33) at the wavelength of 830 nm for polymer thin film poled around Topt was up to 42 pm/V, and the value remained well at elevated temperatures for move than 120 hours in the air.
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