Biocatalytic Polyester Synthesis in Supercritical Carbon Dioxide, Ionic Liquids and Organic Solvents

摘要

The use of enzymes as catalysts in chemical reactions has been an intense area of research for many years. Biocatalysis allows for reactions which would normally require high temperatures and pressures, as well as corrosive acid catalysts, to be carried out at ambient conditions while being highly selective. By pairing enzymes with environmentally benign solvents, such as supercritical carbon dioxide and ionic liquids, the detrimental impact of traditional chemical processes on the environment could be significantly reduced.Polyester synthesis in supercritical carbon dioxide would allow for the rational control of polymer molecular weight and dispersity due to the solvent tunability of supercritical fluids. In order to overcome poor monomer solubility in carbon dioxide, fluorinated monomers were substituted. Thus, fluorinated polyester synthesis was performed from activated diesters and fluorinated diols and the factors that would limit chain extension were assessed. Weight average molecular weights of up to 8094 Da were achieved. The phase behavior of each monomer, as well as the polyester product, was also studied. Additionally, hydroxylated monomers were incorporated into the synthesis in order to produce polyesters that had fluorinated, hydrogenated, and hydroxylated segments.In the Novozym® 435-catalyzed reaction between divinyl adipate and 1,4-butanediol, carbon dioxide was also employed as a viscosity reducing agent in order to alleviate some of the mass transfer limitations that occur during the polymerization. The presence of CO2 did enhance polymer molecular weight but only at reaction times of 1 hour or less. At reaction times longer than 1 hour, the presence of CO2 hindered the achievable molecular weight. Ionic liquids are another environmentally friendly solvent in which enzymatic reactions can be carried out. The enzymes Novozym® 435 and porcine pancreatic lipase were found to show enhanced stability in an ionic liquid when compared to a traditional organic solvent. The biocatalytic polymerization between divinyl adipate and 1,4-butanediol was carried out in this medium but polymer molecular weight was limited due to the precipitation of the polymer from the ionic liquid.