Coupling of CO_(2) and CS_(2) with Novel Oxiranes: Polycarbonate vs. Cyclic Carbonate Production

Polycarbonates are a type of engineering thermoplastic that have countless uses in modern society. Currently, the major industrial production of polycarbonates involves the polycondensation of a diol and phosgene or phosgene derivative. Though there are many advantages to this process, it creates large amounts of waste and requires dangerous chemicals in order to proceed. Over the past four decades, the coupling of CO_(2) and epoxides has grown into a viable, greener alternative for the production of select polycarbonates. The byproduct of this reaction, cyclic carbonates, also have use as polar, high boiling solvents.

This dissertation will be divided into three parts. First, the coupling of indene oxide and CO_(2) to form poly(indene carbonate) and cis-indene carbonate will be discussed. Poly(indene carbonate) has the highest Tg yet reported for polymers derived CO_(2) /epoxides coupling, up to 138degreeC. Polycarbonate production requires the use of (salen)Co(III) catalysts and low temperatures, though some cyclic carbonate production is still observed. Selective production of poly(indene carbonate) has been achieved through the use of bifunctional cobalt(III) complexes. The effects of temperature and cosolvent choices on polymer production will be thoroughly discussed.

Though polycarbonate is the kinetic product from the coupling of CO_(2) and epoxides, the thermodynamic product is cyclic carbonate. There are six potential mechanisms that yield this undesired byproduct, though there is limited research into which pathways are the most active during polymerization reactions. Temperature-dependent kinetic studies were performed to obtain the activation parameters for the direct, polymer-free coupling of cyclopentene oxide, indene oxide, 1,2-butylene oxide, and styrene oxide with CO_(2) utilizing (salen)CrCl/nBu_(4)NCl to yield their corresponding cyclic carbonates. Additionally, the metal-free backbiting of the singly-coupled styrene oxide/CO_(2) intermediate was simulated utilizing the halohydrin 2-chloro-1-phenylethanol.

Finally, the coupling of cyclopentene oxide with carbon disulfide to yield poly[thio]carbonates and cyclic [thio]carbonates utilizing (salen)CrCl/PPNX will be discussed. In each reaction, scrambling of the oxygen and sulfur atoms in both the polymeric and cyclic product is observed. Long reaction times lead to increased amounts of [thio]ether linkages and therefore polymers with lower glass transition temperatures. Insights into both the coupling and scrambling mechanisms will be presented.