Poled Polyimides for Thermally Stable Electro-Optic Materials

ABSTRACTUsing polyimide as host in a guest-host electro-optic (EO) thin film a thermally stable poled electro-optic response is demonstrated at temperatures at 150 °C and 300 °C. Electric field poling during curing process including imidization (170 -230 °C) and densification (340 -380 °C) accounts for the highly thermally stable EO response. As a room temperature curing process, chemical imidization is employed as a novel curing process. Dehydration occurring through imidization of the polyamic acid is completed chemically after poling rather than thermally during poling. After thermal aging at 155 °C (above the poling temperature) chemically imidized samples retain over 30% of their original poling induced EO signal while similarly poled samples, which have not been chemically imidized, produce a null EO response. For a class of polyimides possessing aliphatic structure, the thermoplastic behavior of cured guest-host polyimide system allowed the electric field poling at temperatures above the glass transition temperature (Tg). One example of polyimide doped with 10% nonlinear optical molecules exhibits Tg near 200 °C, leading to an excellent thermal stability of the poled EO response with a depoling knee-temperature of 150°C.