Lavoie, Gino G.Campos Rivera, Lya Evelyn2025-04-102025-04-102024-08-212025-04-10https://hdl.handle.net/10315/42789Aluminum and zinc complexes bearing bidentate guanidine-ethenolate ligands are reported and used in the solvent-free polymerization of rac-lactide at 130 °C. Solid-state structures of the zinc complexes showed a distorted tetrahedral geometry. Solid-state structures of the bischelated aluminum complex showed dynamic trigonal pyramidal and square-based pyramidal geometries. The spectra provide evidence of hydroxy and L1H end group for PLA generated from Zn(L1)2 with and without BnOH, as well as from Zn(L1)Et with BnOH. These terminated PLA chains result from water contaminants present in LA. However, it remains challenging to determine whether AMM or CIM is the dominant mechanism. In contrast, Zn(OBn)2, both with and without BnOH, generated polymers with hydroxy, OBn, and macrocycles sodium adducted cationized open chain polymers. The presence of OBn end groups indicates that the polymerization proceeded through CIM. All spectra indicated transesterification side reactions present due to peak separations of m/z 72 g/mol. The π-accepting properties of the guanidine moiety in the Zn(Lx)2 complexes, as estimated by the 31P NMR chemical shift of the corresponding N-heterocyclic carbene–phosphinidene adduct, resulted in a negative correlation in the rate for the ROP of LA polymerization using zinc complexes produced polylactic acid (PLA) with a heterotactic bias (Pr = 0.52–0.65) with molecular weights comparable to those obtained in the SnOct2 control experiment. The most active zinc catalyst reported herein, Zn(L1)2 is only about three times less active than SnOct2, for the ROP of rac-LA at 130 ℃. For the polymerization of L-LA under industrial conditions, at 150 ℃, Zn(L1)2 is only about 14.4 times slower compared to Sn(Oct)2, and about only 2.5 times slower compared to Herres-Pawlis et al. zinc(II) Schiff base complex. Interestingly, the addition of benzyl alcohol as a co-initiator for the polymerization using Zn(L1)Et readily produced Zn(L1)2 and Zn(OBn)2, with both complexes giving comparable activities. Polymerization studies showed that Zn(OBn)2 is only 2.5 times less active than Sn(Oct)2 but with twice as large molecular weights. The Zn(L5)Et complex, in the presence of BnOH, resulted in a reaction rate three times faster than the monochelated guanidine-ethenolate Zn(L1)Et complex, due to the enhanced Lewis acidity of the metal center caused by the presence of the CAAI fragment. MALDI-TOF MS was used to determine the end groups of the polymer chain.Author owns copyright, except where explicitly noted. Please contact the author directly with licensing requests.Electronic Thesis or Dissertation2025-04-10LactideZinc catalystTin octoatePolymerizationRing opening polymerizationGuanidinesGuanidinatesNHCNHICAACCAAIChemistryInorganic chemistryMaterial chemistryPolymer chemistry