A strong understanding of the coordination-insertion mechanism(s) at play in the ring opening transesterification polymerization (ROTEP) of lactones is a prerequisite to rational design of metal-alkoxide catalysts for synthesis of sustainable polymers. Mechanistic studies of ε-caprolactone (CL) and rac-lactide (LA) conducted with tetramethyl-5,7,12,14-dibenzo-1,4,8,11-tetraaza[14]annulene (TMTAA) aluminum ethoxide and (R-salan)zinc alkoxide (R = OMe, Br, NO2) complexes provide insight into steric and electronic effects controlling polymerization rates, molecular weight distribution, and isotacticity. Reaction rates of these sustainable polymers monitored by 1H NMR and, for reactions too fast for NMR, in situ FT-IR (ReactIR) show the extrema of lactone polymerization rates from the slowest aluminum alkoxide to one of the fastest measurable zinc alkoxide catalysts. The basis for the stark contrast between these metal-alkoxide complexes will be discussed.

Steric, electronic, and geometric effects on the ring opening transesterification polymerization mechanism for sustainable poly(lactones) with aluminum and zinc alkoxide catalysts

253rd National Meeting (2017)

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