Metal-free terpolymerization of propylene oxide, carbon dioxide, and carbonyl sulfide: A facile route to sulfur-containing polycarbonates with gradient sequences

Introducing sulfur atoms into polycarbonate can improve its optical properties, but is limited by the lack of efficient synthetic methods. Here we develop a facile method to achieve the one-pot/one-step incorporation of sulfur atoms into polycarbonate chains using raw chemicals of propylene oxide (PO), carbon dioxide (CO2), and carbonyl sulfide (COS). The metal-free Lewis acid-base pair composed of N, N-dimethylcyclohexylamine combined with triethyl borane can effectively catalyze the terpolymerization of PO, CO2, and COS, affording a sulfur-containing polycarbonate with high molecular weight (M-n) up to 58.4 kDa and narrow dispersity (D = 1.24-1.56). The obtained terpolymers display gradient sequence with tunable thiocarbonate units (27%-81%) upon simply varying the feed ratio of COS. The refractive indices of the terpolymers can be enhanced up to 1.55 at high thiocarbonate content, suggesting promising applications of the terpolymer in optical materials.