Zinc-Based Catalyst for the Ring-Opening Polymerization of Cyclic Esters

A zinc-based catalyst zinc bis[bis(trimethyl-silyl) amide] was used for the polymerization of cyclic esters including L-lactide (L-LA) and 2-methyl-2-carboxyl-propylene carbonate (MBC). The polymerization of L-lactide in THF could be carried out successfully under mild conditions in very short time by using the zinc catalyst and alcohols as the initiators. Kinetic study in solution polymerization prooved the polymerization has high monomer conversion degree close to 100% and the molecular weight of the resulting polyester has linear increase with the increase of [M](0) /[I] (molar ratio of monomer to initiator). Sequential polymerization of L-LA and MBC in THF also showed high MBC conversion of 94% with a narrow molecualr weight maintained, indicating a living nature of this polymerization. The zinc catalyst system has also been used for the L-LA bulk polymerization with a high monomer conversion. C-13 NMR indicated the polymer possesses high regioregularity and the minor regioirregular component was owing to the D-LA in the monomer inserted into the polymer mainchain during the transesterifcation. Interaction between monomer and zinc catalyst has been found to be a key factor to sustain a homogenous solution during the initiating procedure. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 2378-2385, 2011