Enhancing flame retardancy and mechanical performance of polycarbonate with cinnamate-containing liquid crystalline copolyester

The flame-retardant modification of polymers, while preserving or enhancing their mechanical properties, is critical for engineering plastics. In this study, we develop flame-retardant polycarbonate (PC) composites with improved mechanical performance by incorporating cinnamate-containing liquid crystalline copolyester (CLCP). During the injection molding process, CLCP forms oriented microfibrils in situ, boosting the tensile strength of the composites by up to 66 %. The cinnamate groups in CLCP undergo radical-initiated thermal crosslinking, which increases melt viscosity, prevents dripping, and achieves a UL-94 V-0 rating. The primary flame retardancy mechanism occurs in the condensed phase: early decomposition of CLCP triggers thermal crosslinking, leading to the formation of a dense, graphitized char layer that reduces the peak heat release rate (PHRR) by 46.8 %, total smoke production by 17.9 %, and increases the limiting oxygen index (LOI) to 32.5 % (compared to 27.0 % for neat PC). This dual-functionality of CLCP addresses both the flammability and mechanical limitations of PC, making it a promising candidate for engineering applications requiring high-performance materials. This work introduces a novel molecular design strategy, integrating liquid crystallinity and cinnamate crosslinking, to enhance both flame resistance and mechanical properties in engineering plastics.