Guaiacolate derivatives-containing sodium complexes as catalysts for l-lactide polymerization

In this study, guaiacolate derivatives-containing tetranuclear sodium catalysts were synthesized, and their catalytic activity in l-lactide (LA) polymerization was evaluated. Using L-BF-Na (sodium complex bearing 2,3-dihydro-2,2-dimethyl-7-benzofuranolate) as a catalyst, the polymerization of LA was studied in various solvents. L-BF-Na polymerized LA in dichloromethane, tetrahydrofuran, and toluene, and the catalytic activity of L-BF-Na was similar in these solvents. Among the sodium complexes, L-OH-Na (sodium complex bearing guaiacolate) exhibited higher catalytic activity (5 min, conversion = 93%; Mn-GPC = 7200) than the other tetranuclear sodium complexes. Furthermore, L-OH-Na exhibited an "immortal" property after 20 equivalents of benzyl alcohol loading during LA polymerization and good controllability in polylactide production. Thus, guaiacolate ligands increase the catalytic activity of sodium catalysts in LA polymerization in both coordinating and halogen-containing solvents and under the condition of extra alcohol loading.