Effect of ring size on the cationic ring-opening polymerization of cyclic sulfites

The cationic polymerization of five- and eight-membered cyclic sulfites (5CS and 8CS) was examined. The monomer 5CS polymerized in the presence of cationic initiators such as TfOMe, BF3 · OEt2, and TsOMe in bulk to afford a polyether, accompanied by quantitative desulfoxylation. On the other hand, 8CS polymerized without desulfoxylation. Ring strains of 5CS and 8CS were evaluated by molecular orbital (MO) calculations, which confirmed the larger ring-strain of 8CS compared with 5CS.