Novel melamine-based porous organic materials as metal-free catalysts for copolymerization of SO2 with epoxide

Copolymerization of SO 2 with epoxide into the poly(cyclohexene sulfite) (PCS) is crucial due to the severe harm of SO 2 to the environment and the wide application need of the PCS product. However, the copolymerization tends to exhibit low conversion rate even under harsh conditions. The introduction of high-efficiency catalysts is an efficient way to solve the problem of limitation of SO 2 copolymerization. Herein, the novel and metal-free Schiff-base network (SNW) material, SNW-KUST1, was successfully designed and structurally characterized, which exhibits an excellent catalytic performance for the copolymerization of SO 2 and cyclohexene oxide with a record PCS selectivity of 93%. In comparison with the SNW-1, the catalytic activity of SNW-KUST1 is greatly improved, which can be attributed to the introduction of hydroxyl and increasing specific surface area. Moreover, the SNW-KUST1 can be reused more than 6 times without obvious decrease of the catalytic activity, and presents a wide applicability to various epoxides. A possible mechanism for the SO 2 copolymerization over SNW catalysts is proposed which includes the epoxide adsorption, ring-opening of epoxide, SO 2 insertion and the formation of PCS. It is an optimistic hope that this investigation can give a valuable guideline to design SNW materials with π-π conjugated and nitrogen-rich building blocks for the SO 2 copolymerization.