Exploration of Bis(imino)pyridine Iron Alkoxides for the Synthesis of Novel Degradable Polymers

Thesis advisor: Jeffery A. ByersThis dissertation discusses the development of a family of iron complexes and their role in the synthesis of degradable polymers. Chapter one will introduce the different areas of redox-switchable polymerization. In chapter two the synthesis of block copolymers containing a polyester and polyether block is presented. The application redox-switchable polymerization to form a copolymer with two fundamentally distinct backbone functionalities and their characterization is discussed. In chapter three the synthesis of a degradable cross-linked polymer through a novel redox-triggered cross linking event is summarized. In chapter four, a detailed mechanistic study of iron-complex catalyzed epoxide polymerization is examined and a unique mechanistic scheme is proposed. Lastly, in chapter five the synthesis and characterization of a formally iron(I) complex is presented. This complex shows remarkable catalytic activity towards ring-opening polymerization.Thesis (PhD) — Boston College, 2018.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Chemistry

Designing Thermally Stable Organocatalysts for Poly(ethylene terephthalate) Synthesis: Toward a One-Pot, Closed-Loop Chemical Recycling System for PET

Organocatalysis provides robust methodology to furnish “greener” routes to polymer synthesis. However, the application toward the synthesis of aromatic polymers via step-growth polymerization is an area that justifies more investigation, as a consequence of the poor thermal stability of many organic catalysts and the high reaction temperatures commonly required. In this study, thermally stable organic salts consisting of an organic base and an organic acid were explored to understand key elements required for the bulk synthesis of poly(ethylene terephthalate) (PET) at 270 °C. The ΔpKa values of the salts played an important role in the thermal stability such that the salts with higher ΔpKa values showed higher stability because of the strong acid–base interactions. The 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) salts with high ΔpKa values (≥16.9) showed the best catalytic activity among the investigated salts in terms of both low amounts of side reactions and discoloration. The thermal and chemical stability of the salts also affected the polymer properties. Dimerization side reactions that lead to defects in the polymer backbone were found to occur more readily in salts containing strong acids as components, particularly as the ΔpKa between the acid–base components decreased. The discoloration of the PET sample was also correlated to the thermal stability of the organic salt catalyst, with a lower stability generally leading to enhanced discoloration likely due to decomposition of base components. Polymerization–depolymerization cycles were also investigated with the TBD:p-toluenesulfonic acid (TSA) salt and the feasibility of simple, closed-loop recycling of PET with the system was established

1, 3-γ-Silyl-elimination in electron-deficient cationic systems.

Placement of an electron-withdrawing trifluoromethyl group (–CF3) at a putative cationic centre enhances γ-silyl neighbouring-group participation (NGP). In stark contrast to previously studied γ-silyl-substituted systems, the preferred reaction pathway is 1,3-γ-silyl elimination, giving ring closure over solvent substitution or alkene formation. The scope of this cyclopropanation reaction is explored for numerous cyclic and acyclic examples, proving this method to be a viable approach to preparing CF3-substituted cyclopropanes and bicyclic systems, both containing quaternary centres. Rate-constants, kinetic isotope effects, and quantum mechanical calculations provided evidence for this enhancement and further elaborated the disparity in the reaction outcome between these systems and previously studied γ-silyl systems