Sulfonyl‐Containing Polycarbonate Copolymer: Ultra‐Thin Flame‐Retardant, Transparency, and High Notched Impact Toughness

Abstract Bisphenol‐A polycarbonate (PC) is facing severe challenges in balancing flame retardancy with optical transparency and mechanical strength, especially in the ultra‐thin configuration required for advanced electronic products and 5G applications. Here, a kind of flame‐retardant polycarbonate (PC‐SDP _n ) is reported and synthesized by interfacial polycondensation of 4,4'‐sulfonyl diphenol (SDP) and bisphenol A. The radical quenching in gas phase, the dilution of combustible gas, and the catalytic char formation in condensed phase can be realized by chemically embedding sulfonyl into the polymer backbone. This molecular design avoids the inherent contradiction in modification based on additives. The PC‐SDP _n showed excellent flame retardancy and fire safety, and it can still pass the UL‐94 V‐0 rating when the thickness is 0.8 mm, the limiting oxygen index increased to 32.1%, the peak heat release rate and smoke production rate decreased by 55.7% and 62.5% respectively. In addition, PC‐SDP ₅ maintains a light transmittance of 89.6% and a notched impact strength of 88.3 kJ m ⁻² , which is superior to most commercial PC. This work shows its application potential in microelectronics and fire‐proof transparent buildings, which require transparency and ultra‐thin flame retardant.