CO ₂ -Mediated Cyclic Carbonate Route to High-Molecular-Weight Optical Resin

A long-standing challenge in the synthesis of optical resins using styrene oxide (SO) is the inevitable SO isomerization side reactions that deteriorate the polymerization, giving low-molecular-weight products. Here, we report a CO2-mediated monomer-protection strategy that converts SO into its stable cyclic carbonate, styrene carbonate (SC), effectively preventing side reactions. Upon thermal activation, SC undergoes selective ring-opening followed by in situ decarboxylation to generate an active species, which is immediately captured by phthalic anhydride (PA) to realize efficient and controlled polymerization. The average molecular weight of the resulting polyesters was significantly increased to 178.4 kDa with a low dispersity (Đ = 1.39) under optimized conditions. Owing to the markedly enhanced molecular weight, the polyesters exhibit superior thermal stability, electrical insulation, optical transparency, and a balanced refractive index (nd = 1.588) and Abbe number (Vd = 42). This work demonstrates a rational, design-driven approach for reprogramming labile epoxides and provides a versatile platform for the synthesis of high-molecular-weight optical resins with potential applications in advanced optical, electronic, and insulating materials.