| Summary: | 博士 === 國立中興大學 === 化學工程學系所 === 97 === Organic nonlinear optical (NLO) materials have been extensively investigated due to their higher bandwidth, larger nonlinearity and lower cost as compared to inorganics. The most important subjects in developing NLO polymers for electro-optical (EO) modulation are whether the polymers possess excellent poling efficiency, temporal stability and low optical loss.
In the previous researches, NLO chromophores are usually incorporated into high glass transition temperature (Tg) polymers and/or crosslinked polymer networks in order to achieve stable optical nonlinearity. However, the high Tg characteristic of polymer allows the NLO-active polymer to exhibit low poling efficiency. The lattice-hardening phenomenon such as the sequential self-repetitive reaction (SSRR) process would be the best choice of the high poling efficiency approach.
A series of thermally stable side-chain NLO poly(amide-imide)s via SSRR have been developed. The difunctional azo chromophores DNDA was respectively reacted with excessive amount of methylene-diphenylisocyanate (MDI) to form polycarbodiimide, and subsequently trimellitic anhydride was added to obtain an intermediate, poly(N-acylurea). After in-situ poling and curing process, N-acylurea moieties were converted to amide-imide structures via SSRR, and the Tgs of the polymers were elevated significantly. For the polymer PIDN with the feed ratio (MDI/DNDA=6/1), the electro-optical coefficients (r33) at 830 nm was around 20 pm/V. In order to improve the thermal stability of NLO polymer, alkoxysilane was used to form semi- interpenetrating polymer network composites via sol-gel process. The side-chain carboxyl acid group of poly(N-acylurea) could act as a binding site for alkoxysilane, and the organic-inorganic compatibility was enhanced as a result. The refractive indices of composites could be controlled by varying the inorganic ratios, and the optical losses of the optical films for the materials were reduced with increasing inorganic content. The layered montmorillonite was also used for enhancing the stability. The ameliorated morphology of nanocomposites due to the rich chemical bonds between the intercalating agent-modified MMT and the polymer chains would bring about better thermal properties. Furthermore, a wholly aromatic polyimide structure was attempted to develop via SSRR. The relaxation peak of polyimide which was measured by the dielectric analyzer at a heating rate of 2 oC/min was higher than that PIDN. Moreover, the optical loss of this polyimide was also lower than that of PIDN.
On the other hand, the optical loss of polymer was improved by fluorinated the polymer chain. Not only could low optical loss (2.0 dB/cm at 1310 nm) be obtained, but excellent temporal stability of EO coefficient was also achieved.
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