No abstract

Diphenyl carbonate is an attractive monomer for copolymerization with Bisphenol‐A to produce the strong, high melting polycarbonate, Bisphenol‐A Polycarbonate. Diphenyl carbonate is an ideal candidate for this polymerization as the phenols constitute good leaving groups during polymerization. Industrially, diphenyl carbonate is produced via the phosgenation of a phenolic sodium salt. Using phosgene creates additional safety hazards as well as concerns in treating or disposing of the reaction by‐products. The enzymatic synthesis of diphenyl carbonate via alcoholysis of dimethyl carbonate by phenol is presented. While the process is environmentally benign and eliminates the considerable safety issues related to the use of phosgene, phenol is a poor nucleophile and conversion to diphenyl carbonate is limited. Enzyme catalyzed condensation polymerization of carbonate monomers and diols is a more feasible and direct enzymatic route to polycarbonate. We describe an AA‐BB condensation polymerization to make polycarbonates using enzymes at ambient conditions. Molecular weights of up to 8,500 MW are achieved. Unlike the industrial polymerization, this process is performed without the use of acid catalysts, significant energy input, or high temperature or pressure. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 62: 259–266, 1999.

Aromatic polymers are widely used in products ranging from optical lenses to milk bottles because of their strength, thermal durability, and high glass transition temperatures. All of the commonly used routes employed to generate aromatic polycarbonates and polyesters generate large amounts of waste as by-products and require high energy input. For these reasons, alternate routes to aromatic polymers which involve either less energy input or less waste generation are being investigated. One such route may be enzymatic. Herein we describe enzyme-catalyzed AA-BB condensation polymerizations to form aromatic polycarbonates and polyesters with six different aromatic diols and molecular weights of up to 5,200 Daltons are generated. In addition, for reactions with benzenedimethanol the enzyme exhibits regioselectivity for parahydroxyls over meta- and orthohydroxyls.

Enzymes are biocatalysts constructed of a folded chain of amino acids. They may be used under mild conditions for specific and selective reactions. While many enzymes have been found to be catalytically active in both aqueous and organic solutions, it was not until quite recently that enzymes were used to catalyze reactions in carbon dioxide when Randolph et al. (1985) performed the enzyme-catalyzed hydrolysis of disodium p-nitrophenol using alkaline phosphatase and Hammond et al. (1985) used polyphenol oxidase to catalyze the oxidation of p-cresol and p-chlorophenol. Since that time, more than 80 papers have been published concerning reactions in this medium. Enzymes can be 10–15 times more active in carbon dioxide than in organic solvents (Mori and Okahata, 1998). Reactions include hydrolysis, esterification, transesterification, and oxidation. Reactor configurations for these reactions were batch, semibatch, and continuous. There are many factors that influence the outcome of enzymatic reactions in carbon dioxide. These include enzyme activity, enzyme stability, temperature, pH, pressure, diffusional limitations of a two-phase heterogeneous mixture, solubility of enzyme and/or substrates, water content of the reaction system, and flow rate of carbon dioxide (continuous and semibatch reactions). It is important to understand the aspects that control and limit biocatalysis in carbon dioxide if one wants to improve upon the process. This chapter serves as a brief introduction to enzyme chemistry in carbon dioxide. The advantages and disadvantages of running reactions in this medium, as well as the factors that influence reactions, are all presented. Many of the reactions studied in this area are summarized in a manner that is easy to read and referenced in Table 6.1. Carbon dioxide is cited as a good choice of solvents for a number of reasons. Some of the advantages of running reactions in carbon dioxide instead of the more traditional organic solvents include the low viscosity of the solvent, the convenient recovery of the products and non-reacted components, abundant availability, low cost, no solvent contamination of products, full miscibility with other gases, non-existent toxicity, low surface tension, non-flammability, and recyclability. The low mass-transfer limitations are an advantage because of the large diffusivity of reactants.