Synthesis and microwave characterizations of crosslinked oligoimide

In this paper, we present the microwave characterization of polymers for el ectro-optic devices, carried out as a collaboration between chemical and ph ysical research groups. We begin by reporting the synthesis and characteriz ation of telechelic oligoimides functionalized with trialkoxysilane end-gro ups. Addition of a crosslinking agent, tris(4-hydroxyphenyl)ethane, and the rmal curing leads to network formation, with the trialkoxysilyl end-groups as crosslinking sites. The network formation is confirmed by FTIR spectrosc opy. The resulting material exhibits a glass transition temperature above 3 00 degreesC and a thermal decomposition temperature above 450 degrees. Thes e oligomers offer an attractive processing alternative as low viscosity pre cursors to polyimide networks. The permittivity from 250 MHz to 40 GHz is determined by spin-coating the p olymer on a structure as close as possible to a travelling wave electro-opt ic modulator. The permittivity is obtained from the measured scattering par ameters and a spectral domain approach (S.D.A.)-based simulation The scatte ring parameters (measured), constant propagation (simulated) and characteri stic impedance (simulated) are linked together using two alternative physic al representations, the multiple reflection method and the attenuation meth od. This approach was first validated with a commercial polymer and then ap plied to the oligoimides. (C) 2000 published by Elsevier Science S.A.