H-bonding Catalyst Systems for the Ring-Opening Polymerization of Cyclic Esters and Carbonates
The overarching theme of my work pertains to the development of catalytic systems to affect the organocatalyzed ring-opening polymerization of cyclic esters and carbonates. Hydrogen bond mediated organocatalysts provide a robust and controllable synthetic route to well defined polyesters and polycarbonates. However, organocatalysts tend to be either highly selective or highly active. This research includes several projects which delve into how changing the H-bonding catalytic systems effects rates of polymerization; specifically, when applied to the organocatalyzed ROP of ϵ-thiocaprolactone (tCL), δ-valerolactone (VL), and ϵ-caprolactone (CL). ^ The first manuscript, “Ring-Opening Polymerization of Thiol Containing Cyclic Carbonate and Lactone Monomers: A Review”, brings together decades of work applied to the ROP of cyclic carbonates and esters and is prepared for publication in Macromolecules. The background presented in manuscript 1 serves to provide the reader with some historical pretext for the following chapters included in this thesis. ^ The second manuscript, “Poly(thioester) by Organocatalytic Ring-Opening Polymerization”, discusses the H-bond mediated organocatalytic ROP of tCL. Previous attempts to polymerize tCL were successful but entailed harsh conditions and high temperatures. In an effort to polymerize tCL utilizing milder synthetic routes and in a “living” manner, several H-bond accepting bases were screened; leading to a broadening of Mw /Mn. However, it was discovered when a H-bond donating thiourea co-catalyst was paired with a H-bond accepting base the unwanted transesterification was suppressed; implicated by the decreased M w/Mn of the base/thiourea catalyzed polymerization of tCl versus the same reaction catalyzed by base alone. All results and work were completed by the author and have been published in Macromolecules in 2015. ^ The third manuscript, “Triclocarban: Commercial Antibacterial and Highly Effective H-Bond Donating Catalyst for Ring-Opening Polymerization”, discusses the application of the recently banned, antibacterial, and commercially available triclocarban (TCC) as a H-bond donating co-catalyst in the base/TCC catalyzed ROP of VL and CL. TCC was shown to be a highly effectiveurea co-catalyst when paired with a H-bond accepting base. When applied to the ROP of VL and CL, the base/TCC mediated polymerizations proceeded in a “living” manner. This simple change from a thiourea to a urea-based H-bond donating co-catalyst proved to be monumental for our group. Additionally, two electronically similar H-bond donating ureas were synthesized and evaluated, mono-CC and di-CC. The urea-based co-catalysts are shown to remain highly active in hydrogen bonding solvents; unlike their thiourea based conjugates. This work was a collaborative effort and the thesis author completed all work encompassing the MTBD/nCTU (n = 2–6 and 12) catalyzed polymerization of VL in acetone- d6, MTBD/TCC catalyzed reaction of CL in benzene- d6, MTBD/di-CC and MTBD/mono-CC catalyzed ROP polymerizations of VL in benzene-d6, and the synthesis of both the di-CC and mono-CC urea co-catalysts. These results were all published in ACS Macro Letters in 2017. ^ The fourth manuscript, “Bis-thiourea mediated organocatalyzed ROP of a cyclic lactone”, investigates the effect that bis-thiourea H-bond donating cocatalysts have on the ROP of VL. Several new thiourea H-bond donating catalysts were developed and applied to the base/nCTU (n = 2–6 and 12) catalyzed ROP of VL in an attempt to increase control and rate of the polymerization. Several bases were examined for their efficacy in the ROP of VL. The application of Michaelis-Menten enzyme kinetics to the MTBD/5CTU catalyzed ROP of VL coupled with the kie of the DBU/5CTU catalyzed ROP of VL led to the conclusion that competitive inhibition exhibits itself. The observations and results were prepared for publication in ACS Macro Letters. ^ The fifth manuscript, “Stilbene Synthesis by Olefin Metathesis Reaction”, changes gears a bit and proposes a new sophomore organic chemistry laboratory. Used as a sequence, Wittig then Metathesis, the student can compare and contrast not only a “non-green” and “green” synthetic approach to stilbene, but also thermodynamic versus kinetic control. However, this work specifically deals with the Gubbs 2 catalyzed metathesis of stilbene. The students conduct an easy 1.5–2-hour experiment and characterize their results by 1HNMR, IR, and meting point. This work was a collaborative effort. The thesis author and Partha Datta both optimized the metathesis reaction catalyzed by Grubbs 2 for the laboratory. A class of Advanced OrganicChemistry students, Partha Datta, and the thesis author shared in data collection and characterization. Overall, the organic lab was a success and was submitted for publication in the Journal of Chemical Education in 2018.^
Organic chemistry|Polymer chemistry
Timothy J Bannin,
"H-bonding Catalyst Systems for the Ring-Opening Polymerization of Cyclic Esters and Carbonates"
Dissertations and Master's Theses (Campus Access).