Characterization of Thermally Stable Dye-Doped Polyimide Based Electrooptic Materials
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ABSTRACT Preparation and characterization of novel dye-doped polyimide films for electrooptics is described. Thermal stabilities of donor-acceptor 2,5-diaryl oxazoles were evaluated by differential scanning calorimetry. Absorptive losses in thin films of Ultradel 9000D® doped with donor-acceptor oxazoles were measured by photothermal deflection spectroscopy. Absorptive losses at high doping levels may be explainable by dye-dye aggregation or dye degradation during the curing process. Lower doping levels, however, show losses of < 3.0 dB/cm at 830 nm and •2.4 dB/cm at 1320 nm.
INTRODUCTION Polymeric electrooptic materials have the potential to replace electronic switches in applications which require minimization of heat dissipation while maintaining high switching speeds. Polyimide matrices incorporating electrooptic dyes are promising materials for such applications due to their low cost and compatibility with existing processing environments. Requirements for practical systems include large electrooptic coefficients, thermal stability, high Tg, refractive index differences (waveguide formation), conductivity (poling and data impression) and low optical loss (transmission).1 (Figure 1). High It8 H
High Tg
Useful
Conductivity
nElectrooptic High Tdec
Material
An
Low loss Figure 1. Property-performance criteria for electrooptic materials. Amoco Ultradel 9000D® aromatic polyimides (Fig. 2, below) are a family of y-butyrolactone (GBL) soluble, fully imidized, fluorinated polyimides developed for integrated optical applications. Thermal or photochemical cross-linking imparts a Tg approaching 400 'C and 467 Mat. Res. Soc. Symp. Proc. Vol. 328. @1994 Materials Research Society
provides stability for poled polymer systems. Excellent optical transparencies have also been 2 demonstrated in these materials.
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Figure 2: Amoco Ultradel 9000D® Electrooptic Polyimides.
Previously we reported results of characterization of Ultradel polyimides for electrooptic applications, as well as properties of these polymers heavily doped with donor-acceptor triaryl azole dyes (1).3 (Figure 3.) In this study we have extended our investigations to examine novel diaryl oxazoles (II) and their properties in polyimide electrooptic films. Computational studies suggested that linear and nonlinear optical properties of diaryl oxazoles should be similar to their triaryl counterparts with the advantage of a higher nonlinearity to weight ratio. Thus, we undertook the synthesis and characterization of novel dyes II a-c.
N
SXO, MeO
A
=
S, NH CN, NO 2 , S0 2CH 3
MeO
A = CN, NO 2 , S0 2CH 3 II a-c
I Figure 3: Donor-acceptor triaryl- and diaryl-azoles.
RESULTS AND DISCUSSION Triaryl oxazoles were prepared in multi-gram lots by condensation of an appropriate benzamide with anisoin in the presence of an acid catalyst. 4 (Figure 4.) A more elaborate route was developed to achieve the regioselectivity required of the diaryl oxazoles. For example, 4cyanobenzoyl chloride was condensed with 2-amino-(4-methoxyphenyl)ethanone via a modified
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