Improving the ring-opening polymerization of ε-caprolactone and L-lactide using stannous octanoate

A series of ligands were tested to meliorate the catalytic activity of epsilon-caprolactone (CL) and L-lactide (LA) polymerization by Sn(Oct)(2) and BnOH. There are seven ligands (methyl 2-(dibenzylamino)acetate (MDBAA), di(1H-pyrazol-1yl)methane, benzanide, 8-aminoquinoline, 2-bromo-1-phenylethanone, 2,6-di-tert-butyl-4-methylphenol, and dipyridine) were found to be useful in increasing the polymerization rate for CL polymerization. For LA polymerization, there are only two ligands (8-aminoquinoline and p-thiocresol) effectively raised the polymerization rate. Moreover, the kinetic study reveals a first-order dependency on [CL] and second-order dependency on [LA], indicating different polymerization mechanisms in Sn(Oct)(2) catalytic system. The mechanistic study also explains that MDBAA could potentially modify the framework of the catalytic intermediate and produce the hydrogen, thereby increasing the rate of CL polymerization.