The complex (tBu-SalAmEE)Al (tBu-SalAmEEH3 = N,N-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-2-(2-aminoethoxy)ethanol) catalyzes the ring-expansion polymerization of lactide to form cyclic poly(lactide). The polymerizations achieve high molecular weights and, in the melt or in solution, display characteristics of a controlled reaction including linear relationships between molecular weight and time or catalyst loading. The proposed monomeric catalyst structure has been crystallographically confirmed. Solution kinetics have determined the order in lactide and catalyst. Variable temperature NMR shows that (tBu-SalAmEE)Al reversibly binds a variety of Lewis bases, although lactide shows no evidence of coordination. Taken together, these data are consistent with a coordination-insertion mechanism whose rate determining step is intramolecular catalyst rearrangement by loss of the hemilabile, datively bound, bridging ligand ether. Some catalyst synthesis conditions yielded a polymetalate that was characterized crystallographically. Several recent reports of unexpected aluminum polymetalates emphasize this as a cautionary tale for metalation using aluminum alkyls.

Lactide cyclopolymerization by (<i><sup>t</sup></i>Bu-SalAmEE)Al: Polymerization mechanism and catalyst characterization

245th National Meeting (2013)

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Lactide cyclopolymerization by (tBu-SalAmEE)Al: Polymerization mechanism and catalyst characterization

Lactide cyclopolymerization by (^tBu-SalAmEE)Al: Polymerization mechanism and catalyst characterization