A series of novel fluorinated polyimides second-order nonlinear optical (NLO) materials were synthesized from poly(hydroxy-imide)s, followed by the Mitsunobu reaction with NLO thiazolylazo chromophores. The polyimides prepared were characterized by IR, UV-vis, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetric analysis (DSC) and X-ray diffraction (XRD). These NLO polyimides possess high glass transition temperature (Tg) in the range of 193-200 °C with thermal stability up to 288 °C. The electro-optic coefficients (r33) at the wavelength of 1550nm for polymer thin films poled were measured by the attenuated total reflection (ATR) method. The r33 values of the polyimides 1a and 2a containing thiazolylazoaniline chromophore are better than that of the polyimides 1b and 2b attached thiazolylazopyrimidine chromophore, due to the thiazolylazoaniline chromophore having large hyperpolarizability in contrast to the thiazolylazopyrimidine chromophore. Low optical losses (1.8-2.1 dB/cm at 1.55 μm), which were measured via an immersion technique have been observed for these polymers. The polyimides demonstrate an excellent combination of thermal stability, electrooptic (EO) coefficients and optical loss, and therefore they are suitable for EO applications.
Polyimide (PI) /silica (SiO2) nanohybrid composite waveguide films prepared from Pyromellitic dianhydride (PMDA), 2,2-Bis(3-amino-4-hydroxyphenyl)hexafluoropropane(6FHP) , nonlinear optical (NLO) molecule, coupling agent APTES and hydrolysate of TEOS via sol-gel process and thermal imidization. The silica content in the hybrid waveguide films varied from 0 to 22.5/wt%. The PI hybrids prepared were characterized by IR, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM),etc. They exhibit fair good optical transparency. The SiO2 phase is well dispersed in the polymer matrix. DSC and TGA results show that these hybrid waveguide materials have excellent thermal stability.
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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