| Summary: | 博士 === 輔仁大學 === 化學系 === 87 === Although polymeric nonlinear optical materials have been developed for many years，poor thermal stability has discouraged consideration of these materials for electonic application. In order to prevent the rotation and translation of the chromophore molecules，several methods have been used to improve the thermal stability： including side chain、main chain、cross-linking、L-B film、liquid crystal and self-assembled superlattice. As for the decrease of the polymer main chain relaxation，high Tg type polymers are always choosed，such as polyimide and epoxy etc.
Silica glass with Tg>1000℃ is an excellent polymer matrix candidate for the thermal stability purpose. The conventional method to produce silica glass needs to raise the temperature up to 1000℃，which is too high for the chromophore. An alternative method is to use sol-gel process. The sol-gel process is a low temperature method for producing a three dimensional silica network by chemical reaction. By chemical bonding (as side chain or crosslinking )the chromophore onto the silica networks may improve the thermal stability and nonlinear optical properties significantly. Besides, highly crosslinked epoxy resin contains extremely high Tg (>160℃) which is also an excellent candidate for NLO polymeric matrix.
We synthesize a series of reactive chromophores which will crosslink onto the silica and epoxy structure. Since the chromophore is part of the backbone，it chould be much more difficult for the chromophore to relax，which should further increase the thermal stability of the second NLO properties.
A series of transparent silica films with organic chromophores as side chain, main chain or crosslinking agent were prepared by the sol-gel process. The resulting films heated at 100 -200℃ under high corona field exhibit d33 =16 -32 pm/V, in the Maker-fringe measurement. The S-Ch 8-4 film shows excellent temporal stability. The d33 signal remained at 86% of its initial value after heating even at 200℃ for 1h.
In order to increase the nonlinear optical chromophore concentration and the crosslinking density, the crosslinkable NLO dye , Ch 7, was processed and poled in the epoxy-based nonlinear optical (NLO) polymeric material . After crosslinking at 150℃for 8h, the glass transition temperature (Tg) of the polymer increased to 175℃ . It exhibits a d33 value of 23pm/V and retains 77% of its original value after being subjected to thermal treatment at 100℃for 1h.
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