The development of dinuclear zinc catalysts for the copolymerization reaction of carbon dioxide and epoxides to produce polycarbonates

The synthesis of a class of dimeric zinc catalysts with a general formula [(O-2, 6-X₂C₆H₃)₂Zn(THF)] ₂ used for the copolymerization of CO₂ and epoxides is described herein. Using phenoxide ligands with small halogenated groups render the catalyst dimeric in nature as opposed to previously designed monomeric zinc phenoxide catalyst with bulky alkyl and aryl substituents. These dimeric zinc catalysts influence and greatly enhance the properties of the resulting polycarbonate by maximizing CO₂ incorporation. The CO₂ incorporation into the propagating polymer chain has always been plagued in the past by the competitive formation of polyether linkages due to consecutive epoxide insertions. In addition, phosphinated zinc adducts, along with their corresponding cadmium adducts, have been synthesized, characterized and tested for their ability to withstand the addition of excess base and variances in temperature. As with the halogenated zinc phenoxides, halogenated zinc benzoate complexes have also been synthesized, characterized and tested for their ability to perform this coupling process. These complexes have been characterized as dinuclear or multinuclear soluble clusters.; Model complexes for the development of single site catalysts have been synthesized and characterized. These complexes have the general formula [(C ₅R₄C₂H₄NR′ ₂)Zn(μ-OAc)]₂ and are dimeric in nature. Regrettably, the catalysts are unstable under the reaction conditions of 30°C–80°C and pressures greater than 600 psi required for the CO₂/epoxide coupling process to take place, thereby providing poor turnover frequencies and polymer properties.; Lastly, an analysis and survey of the physical properties of a polycarbonate produced through this alternate route have been performed and are described herein. A variety of physical and mechanical properties concerning strength, clarity, and processability of the polymer have been determined. The physical and tensile properties of poly(cyclohexenylene carbonate) have been found to be not competitive with Bisphenol-A polycarbonate. Further comparison of the properties of poly(cyclohexenylene carbonate) with industrially produced Bisphenol-A polycarbonate has been made and is discussed herein.