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Chris Schaller, Chemistry


The goal of this research is the synthesis of a phenol-containing transition metal complex with a carbene unit that can effectively catalyze the ring-opening polymerization (ROP) of cyclic esters such as caprolactone, lactide, and menthide. Although catalysts such as tin octoate and triethylaluminum are typically used for ROP of cyclic esters, they are toxic. Hence there is a demand for catalysts that are faster, more efficient, and less harmful. While carbene ligands have been documented as effective catalysts for ROP of cyclic esters, less is known about the catalytic abilities of these ligands when bound to a labile metal center such as aluminum. A previously developed catalyst with an aluminum center that works faster than tin octoate and triethylaluminum proved unreliable as it decomposes over a short period. This research focuses on increasing its reliability by replacing an ethyl ligand in the complex with a bifunctional alcohol initiator 1,4-butanediol to allow the formation of a telechelic polymer. In addition, the THF ligand was replaced with other solvents. The aluminum-based complex combined with the 1,4-butanediol initiator resulted in some of the highest degrees of polymerization reaching over 160 units in length and increased control over the polymer chain length. Replacement of THF with solvents such as toluene resulted in the growth of chains ranging from 16-35 in length by varying feed ratios. This work is important as there is a high demand for biodegradable polymers such as polycaprolactone, polylactide, and polymenthide by biomedical, pharmaceutical, and industrial fields.