Amine-bis(phenolate) complexes of chromium for carbon dioxide/cyclohexene oxide copolymerization and group(I) and (II) complexes for the ring opening polymerization of rac-lactide

Devaine-Pressing, Katalin (2017) Amine-bis(phenolate) complexes of chromium for carbon dioxide/cyclohexene oxide copolymerization and group(I) and (II) complexes for the ring opening polymerization of rac-lactide. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Finding novel methods for polymer synthesis has been of particular interest as of late from both a chemical and commercial standpoint. This focus stems from the recognized need for biodegradable and biocompatible polymers, originating from renewable resources, and is a legitimate endeavor by society to ease the burden imposed on the environment. Society’s conscience also recognizes the great need to utilize the carbon dioxide that is released in the atmosphere and it continues to make noble efforts in order not to contribute further to the greenhouse effect caused by greenhouse gases such as carbon dioxide. Therefore, the use of carbon dioxide as a starting material and the incorporation of it in the product of a chemical synthesis are currently developing research areas. Accordingly, combining the aim of environmentally friendly polycarbonate synthesis with incorporation of carbon dioxide in the polymer chain was the goal of the research conducted in the first part of this thesis. Additionally, biodegradable and biocompatible polylactide from lactide, originating from renewable feedstocks, was produced by biocompatible complexes in the second part. Polycarbonate synthesis was carried out in the presence of novel chromium(III) catalysts which were synthesized via salt metathesis reactions from tetradentate tripodal amine-bis(phenol) ligands. The complexes were characterized by MALDI-TOF mass spectrometry, UV-Vis and IR spectroscopy, magnetic susceptibility measurement and elemental analysis. The catalyst precursors selectively produced polycarbonates from epoxides and carbon dioxide with high yields and moderate molecular weights. Mechanistic studies revealed a first order dependence on catalyst concentration and that ring opening of the epoxide was initiated by a nucleophilic species originating either from the complex or from an externally added nucleophile. Biocompatible magnesium-, lithium-, sodium-, potassium- and calcium complexes of an amino-bis(phenolato) ligand were also prepared and characterized for the synthesis of polylactide, a biodegradable and biocompatible polymer. The magnesium and the sodium complexes in particular showed high catalytic activity and good control over the reaction. The complexes were active even under relatively low catalyst loading (0.1 – 0.2 mol%) and produced polymers of high purity as revealed by NMR, DSC and TGA.

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