H-Bonding Catalyst Systems for the Ring-Opening Polymerization of Cyclic Esters and Carbonates

Abstract

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 Mw/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 effective urea 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