Thermally Stable Electrooptic Diazirine-Based Polymers via Carbene Insertion Cross-Linking

Electro-optic (EO) polymers are promising for high-performance modulators due to their high EO coefficients, yet maintaining alignment stability at elevated temperatures remains challenging. While current strategies rely on thermal cross-linking or specific photoreactive groups, a novel diazirine-based carbene insertion strategy was first proposed to enhance the thermal stability and long-term electro-optic performance of the resulting polymers. A custom-synthesized poly(methyl methacrylate) cross-linker (PW1) containing trifluoromethyl-diazirine groups generates highly reactive carbenes upon UV exposure, which insert indiscriminately into C–H bonds─enabling covalent cross-linking without requiring custom-designed chromophores. This approach significantly broadens the applicability of photo-cross-linking to unmodified EO systems. We demonstrate that the glass transition temperatures (Tg) of polymer materials cross-linked via photo-cross-linking and thermal cross-linking exceed 170 and 200 °C, respectively. The EO films treated with these cross-linking methods maintained over 93% of their initial EO efficient (r33) values after 500 h at 85 °C. The carbene-mediated cross-linking offers a versatile, efficient route to enhance thermal stability in EO polymers, compatible with standard photolithography and scalable device integration.