Metal salen catalyzed production of polytrimethylene carbonate
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Over the past decade the focus of our group has been production of polycarbonates through environmentally friendly routes. Continuing with this tradition, one such route is the ring opening polymerization of cyclic carbonates. The aliphatic polycarbonate derived from trimethylene carbonate, (TMC, 1, 3-dioxan-2-one), has been studied extensively for its potential use as a biodegradable polymer in biomedical and pharmaceutical systems. Its important applications include sutures, drug delivery systems and tissue engineering. To date, majority of the literature concerning catalysts for polymerization of TMC has been restricted to the use of simple Lewis acids with a marked absence of well defined and characterized catalysts. Metal salen complexes have been effective in the ring opening of cyclohexene oxide and the copolymerization of epoxide and carbon dioxide. The ability of this system as a catalyst for the polymerization of cyclic carbonates to polycarbonates is reported in this dissertation. The salen ligand is among the most versatile ligands in chemistry. Our attempts to optimize the catalytic activity by manipulating the salen structure and reaction conditions are also discussed. Our initial efforts were concentrated in understanding the efficacy of Lewis acidic metal salen complexes (Al & Sn), as catalysts for this process. This was followed by the utilization of metal salen complexes of biometals as catalysts for the synthesis of these biodegradable polymers, as well as for the copolymerization of cyclic carbonates with cyclic esters. These copolymers are presently in great demand for their applications as sutures in the medical industry. During the course of our investigations, a novel method of synthesizing polytrimethylene carbonate, by the copolymerization of CO2 and trimethylene oxide, has come to our attention. Surprisingly this reaction has received very little scientific exposure. We observed that metal salen derivatives, along with n-alkyl ammonium salts, were effective catalysts for the selective coupling of CO2 and oxetane (trimethylene oxide) to provide the corresponding polycarbonate with only trace quantities of ether linkages. A section is also dedicated to our investigations in this area of research.
Ganguly, Poulomi (2006). Metal salen catalyzed production of polytrimethylene carbonate. Doctoral dissertation, Texas A&M University. Available electronically from