Enzyme catalysis polyester synthesis

The conventional synthesis of aliphatic polyesters based on adipic acid and a range of diols, such as 1,4-butanediol or 1,6-hexanediol, involves a high-temperature esterification reaction typically at 240-260 °C and an organometallic catalyst such as stannous octano-ate. The use of enzyme catalysis results in a much lower reaction temperature, but also the possibility of removing the esterification catalyst, giving the polyester significantly improved hydrolysis resistance. 

Gross, R.A. Kalra, B. Kumar, A. Polyester and polycarbonate synthesis by in vitro enzyme catalysis. Appl. Microbiol. Biotechnol. 2001, 55 (6), 655-660. 

On the other hand, highly selective enzymatic catalysis has been used to modify sugars containing multiple hydroxyl groups in microaqueous media. Enzymes are non-harmful catalysts which catalyze under mild conditions. Recent advances in enzymatic catalysts would be useful tools not only for polyester synthesis but also for vinyl monomer synthesis (96). 

Other grafts to natural materials are exemplified by Dordick s work [173] in which he produced polyesters from sugars and polycarboxylates by enzyme catalysis of the condensation polymerization. These polymers and the method of synthesis may well be the future of renewable resource chemistry. 

This special volume on the enzyme-catalyzed synthesis of polymers focuses on various methods of polymer synthesis using enzymes as catalysts. There are three cases for such synthetic processes (1) In hving cells (in vivo) enzymes catalyze the synthesis of all biopolymers besides other biological substances via biosynthetic (metabolic) pathways, hi test tubes (in vitro) enzymatic catalysis is achieved for the synthesis of polymers via (2) biosynthetic pathways or (3) non-biosynthetic pathways. The present volume is concerned with case (3). Therefore, studies such as the synthesis of polyesters via fermentation using micro-organisms and synthesis of proteins using E. coli are not included. 

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. 

Enzymes may be classified generally into six groups the details of typical polymers produced via catalysis with respective enzymes are listed in Table 23.1. In the past, the target macromolecules for enzymatic polymerization have included polysaccharides, poly(amino acid)s, polyesters, polycarbonates, phenolic polymers, poly(aniline)s, and vinyl polymers. In this chapter, attention is focused on the enzymatic synthesis of phenohc polymers and polyesters, based on the increasing industrial application of these materials. Notably, most such polymers can be obtained from commercially available, inexpensive monomers by using industrially produced enzymes. Another important point is that the enzymatic process must be regarded as an environmentally benign synthetic pathway. Details of the enzymatic synthesis of other polymers are provided in recent pertinent reviews [3-10]. 

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