Long‐Term Stability of Quadratic Nonlinear Optical Response of Polymer Composite Materials via Polymer Chains Cross‐Linking

ABSTRACT The development of composite polymer materials with quadratic nonlinear optical (NLO) activity is presented; long‐term stability of NLO response is provided by polymer chains cross‐linking. For this purpose, polymer matrices based on methyl methacrylate and glycidyl methacrylate copolymers ( P1 ) or hydroxyethyl methacrylate ( P2 ) containing epoxy and hydroxyl groups, respectively, intended for polymer chains cross‐linking, were synthesized. Based on these copolymers, quinoxaline chromophores and cross‐linking agents (succinic acid, terephthalic acid, and 4,4′‐diphenylmethane diisocyanate), polymer composite materials were developed that exhibit quadratic NLO activity up to 37 pm/V for the best samples. Composites were poled to achieve chromophores' polar order in the material necessary for the quadratic NLO response; polymer matrix chains were cross‐linked during poling. An extremely important role of time–temperature poling protocols for the materials' enhanced NLO response is demonstrated. The materials were shown to exhibit high relaxation stability of the NLO coefficient, d 33 : 92%–95% of the initial value preserved after keeping at ambient temperature for several months; after heating at 55°C for 50 h, d 33 for non‐crosslinked samples decreases noticeably (to 80%–86%), while cross‐linked samples keep d 33 unchanged.