Enzymatic Synthesis of Polyesters

Enzymes are generally classified into six groups. Table 1 shows typical polymers produced with catalysis by respective enzymes. The target macromolecules for the enzymatic polymerization have been polysaccharides, poly(amino acid)s, polyesters, polycarbonates, phenolic polymers, poly(aniline)s, vinyl polymers, etc. In the standpoint of potential industrial applications, this chapter deals with recent topics on enzymatic synthesis of polyesters and phenolic polymers by using enzymes as catalyst. 

Polycondensation of dicarboxylic acids or their derivatives with glycols 

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The enzymatic synthesis of polyesters from activated diesters was achieved under mild reaction conditions. The polymerization of bis(2,2,2-trichloroethyl) glutarate and 1,4-butanediol proceeded in the presence of PPL at room temperature in diethyl ether to produce the polyesters with molecular weight of 8.2 x 10. Vacuum was applied to shift the equilibrium forward by removal of the activated alcohol formed, leading to the production of high molecular weight polyesters. The polycondensation of bis(2,2,2-trifluoroethyl) sebacate and aliphatic diols took place using lipases BC, CR, MM, and PPL as catalyst in diphenyl ether. Under the... 

Various combinations of dicarboxylic acid derivatives and glycols enzymatically afforded polyesters under mild reaction conditions. Dicarboxylic acids as well as derivatives, activated and non-activated esters, cyclic acid anhydride, and polyanhydrides, were found to be useful as monomer for the enzymatic synthesis of polyesters. 

Some proteases show an esterase activity, especially in their catalytic activity for regioselective acylation of sugars. By utilizing this property, enzymatic synthesis of polyester containing sugar group in the backbone was demonstrated... 

Fig. 12. Enzymatic synthesis of polyester macromonomer and telechelics by terminator method...

Matsumura S. Enzymatic Synthesis of Polyesters via Ring-Opening Polymerization. Vol. 194, pp. 95-132. 

This section describes the synthesis of oxazolidine esters used as polymer hardeners that cannot be synthesized using chemical catalysis, the synthesis of polyurethane polymers with methods that avoid the use of isocyanates and the enzymatic synthesis of polyesters with low molecular weight dispersity. 

Uyama H, Takamoto T, Kobayashi S (2002) Enzymatic synthesis of polyesters in ionic liquids. Polym J 34 94-95... 

Athawale, V.D., and Gaonkar, S.R. (1994) Enzymatic synthesis of polyesters by lipase catalysed polytrans-esterification. Biotechnol. Lett., 16 (2), 149-154. 

Shuai, X., Jedlinski, Z., Kowalczuk, M., Rydz, J., and Tan, H., 1999, Enzymatic synthesis of polyesters from hydroxyl acids. Europ. Polym J. 35 721-725. 

The enzymatic synthesis of polyesters in green solvents, such as supercritical fluids and ionic liquids, has been demonstrated, in which supercritical carbon... 

Matsumura, S., 2006. Enzymatic synthesis of polyesters via ring-opening pol3fmerization. Advances in Polymer Science 194, 95—132. 

Syntheses of aliphatic polyesters by fermentation and chemical processes have been extensively studied in a viewpoint of biodegradable materials. Recently, another approach of their production has been performed by using an isolated lipase or esterase as catalyst via nonbiosynthetic pathways under mild reaction conditions. Lipase and esterase are enzymes which catalyze hydrolysis of esters in an aqueous environment in living systems. Some of them can act as a catalyst for the reverse reactions, esterifications and transesterifications, in organic media (1-5). These catalytic actions have been expanded to enzymatic synthesis of polyesters. Figure 5 represents three major reaction types of lipase-catalyzed polymerization leading to polyesters (6-14,73). 

In lipase-catalyzed transesterifications, enol esters have been used as acyl agents (4), since the leaving unsaturated alcohol irreversibly tautomerizes to an aldehyde or a ketone, leading to the desired product in high yields. Bis(enol ester)s were reported to be much effective for the enzymatic synthesis of polyesters imder mild reaction conditions (Fig. 6) (108) the polymerization of divinyl adipate and 1,4-butanediol proceeded by lipase PF at 45°C, and adipic acid and diethyl adipate did not afford the pol5mieric materials under the similar reaction conditions. 

Enzymatic synthesis offluorinated polyesters was demonstrated (133). Fluo-rinated diols such as 2,2,3,3-tetrafluoro-l,4-butanediol and 2,2,3,3,4,4-hexafluoro-1,5-pen tanediol were used as glycol substrate and polymerized with divinyl adipate using lipase CA catalyst. The enzymatic synthesis of polyester was also achieved in supercritical fluoroform solvent by the polymerization of bis(2,2,2-trichloroethyl) adipate and 1,4-butanediol (134). The molecular weight increased as a fiinction of the pressure. 

Immobilized lipase showing high catalytic activity toward the enzymatic synthesis of polyesters was demonstrated (178). Only a small amoimt of immobilized lipase PF adsorbed on a Celite was effective for the polymerization of lactones. The catalytic activity was further enhanced by the presence of a sugar or PEG at the immobilization. Surfactant-coated lipase efficiently catalyzed the ring-opening polymerization of lactones in organic solvents, in which the modified enz5mie was soluble (179). 

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