Thermally stable polyimide/silica hybrid: Synthesis, characterization and optical nonlinearity

An intercalation nonlinear-optical (NLO) polyimide was synthesized based on the 3,3′, 4,4′-Bisphenyltetracarboxylic (BPDA) and [(6-nitrobenzothiazole-2-yl)diazenyl] phenyl-1,3-diamine (NBADA). Then, hybrid polymer was synthesized by the sol-gel technique. FT-IR spectroscopy and ²⁹Si NMR were used to characterize the structure of the hybrid. The results revealed that Q³, O₄ and T³ are the major microstructure elements in forming a network structure. The surface morphology, particle size, crystallinity and the thermal stability of the hybrid were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). DSC and TGA results showed that the glass transition temperature (T_g) and the decomposition temperature (T_d) at 5% mass loss were 243, 359°C and 355, 456°C, respectively. These results showed that the hybrid material had excellent thermal stability than the pure polyimide. The electro-optic coefficients of nonlinear optical polyimide and hybrid were measured at the wavelength of 832 nm. The electro-optic coefficients were 22 and 19pm/V (poling voltage of 3.8KV, 210°C) and the values remained well (retained > 93% for more than 100h). The results suggest that the materials have potential applications for high performance optical device.