Synthesis and microwave characterizations of crosslinked oligoimide

Abstract

In this paper, we present the microwave characterization of polymers for electro-optic devices, carried out as a collaboration between chemical and physical research groups. We begin by reporting the synthesis and characterization of telechelic oligoimides functionalized with trialkoxysilane end-groups. Addition of a crosslinking agent, tris(4-hydroxyphenyl)ethane, and thermal curing leads to network formation, with the trialkoxysilyl end-groups as crosslinking sites. The network formation is confirmed by FTIR spectroscopy. The resulting material exhibits a glass transition temperature above 300°C and a thermal decomposition temperature above 450°. These oligomers offer an attractive processing alternative as low viscosity precursors to polyimide networks. The permittivity from 250 MHz to 40 GHz is determined by spin-coating the polymer on a structure as close as possible to a travelling wave electro-optic modulator. The permittivity is obtained from the measured scattering parameters and a spectral domain approach (S.D.A.)-based simulation The scattering parameters (measured), constant propagation (simulated) and characteristic impedance (simulated) are linked together using two alternative physical representations, the multiple reflection method and the attenuation method. This approach was first validated with a commercial polymer and then applied to the oligoimides.