# Enzymatic Synthesis of Biobased Polyesters and Polyamides
## 6 Enzyme-Catalyzed Synthesis of Polyesters
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Enzyme class** & **Reaction catalyzed** & **Typical enzymes** & **Typical polymers** \\ \hline \multirow{4}{*}{EC 1. Oxidoreductase} & \multirow{4}{*}{\begin{tabular}{l} Oxidation/Reduction \\ \(\mathrm{AH_{2}+B\to A+BH_{2}}\) \\ \end{tabular} } & \multirow{4}{*}{\begin{tabular}{l} Peroxidase \\ Lacase \\ \end{tabular} } & \multirow{4}{*}{\begin{tabular}{l} Polyanilines \\ Polyphenol \\ Polystyrenes \\ \end{tabular} } \\  & & & \\ \hline \multirow{4}{*}{EC 2. Transferases} & \multirow{4}{*}{\begin{tabular}{l} Group transfer \\ A-X + B \(\to A+B\)-X \\ \end{tabular} } & \multirow{4}{*}{\begin{tabular}{l} PHA synthase \\ Hylauronan synthase \\ Phosphorylase \\ \end{tabular} } & \multirow{4}{*}{\begin{tabular}{l} Polyesters \\ Hylauronan \\ Amylose \\ \end{tabular} } \\ \hline \multirow{4}{*}{EC 3. Hydrolases} & \multirow{4}{*}{\begin{tabular}{l} Hydrolysis by \(\mathrm{H_{2}O}\) \\ A-B + \(\mathrm{H_{2}O\to AH+}\) \\ BOH \\ \end{tabular} } & \multirow{4}{*}{\begin{tabular}{l} Lipase \\ Cellulose \\ Pajan \\ Papain \\ \end{tabular} } & \multirow{4}{*}{\begin{tabular}{l} Polyesters \\ Polyamides \\ Cellulose \\ (Oligo)peptides \\ Glycosaminoglycan \\ \end{tabular} } \\ \hline \multirow{4}{*}{EC 6. Ligases} & \multirow{4}{*}{\begin{tabular}{l} Bond formation \\ requiring triphosphate \\ \(\sim\) 1 \\ \(\sim\) 1 \\ \(\sim\) 1 \\ \end{tabular} } & \multirow{4}{*}{\
\begin{tabular}{l} Cyanophycin synthetase \\ \end{tabular} } & \multirow{4}{*}{
\begin{tabular}{l} Cyanophycin \\ \end{tabular} } \\  & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Enzymes and typical examples for their use in polymer synthesis, and typical polymers synthesized via enzymatic polymerization [(200)]. The lipase-catalyzed ring-opening polymerization was firstly reported in 1993 by two independent groups [210; 211]. [PERSON] et al. [210] investigated the lipase-catalyzed ring-opening polymerization of \(\epsilon\)-caprolactone (\(\epsilon\)-CL); and polycaprolactone (PCL) with a \(\overline{M_{\rm n}}\) of up to 4400 g/mol was successfully produced in \(n\)-hexane (Scheme 15). At the same time, the enzymatic ring-opening polymerization of lactones was performed in bulk by [PERSON] et al. [211], using different lipases as catalysts. The enzymatic polymerization gave PCL and polyvalerolactone with \(\overline{M_{\rm n}}\)'s of up to 7700, and 1900 g/mol, respectively. Figure 14: Lipase-catalyzed polycondensation of aliphatic diacids and diols. In the late 1990s, the use of N435 in the enzymatic ring-opening polymerization of lactones was introduced by [PERSON] et al. [212] Since then, N435 became the working horse in biocatalytic polyester synthesis. After these pioneer works, various combinations of monomer substrates such as diacids/diesters and diols, hydroxyacids/esters, and cyclic monomers like lactones, cyclic diesters and cyclic ketene acetals, are studied for the lipase-catalyzed polymerization. The recent progress in this field is comprehensively summarized in some review articles [35; 36; 40; 41; 42; 213; 214]. It should be pointed out that the large scale production of aliphatic polyesters via lipase-catalyzed polymerization is feasible. As reported by [PERSON] et al. [215], adipic acid and 1,6-HDO were polymerized by N435 at a multi-kilogram scale, using a two-stage method (Scheme 16). The enzymatic polymerization yielded poly(hexamethylene adipate) with a \(\overline{M_{\mathrm{w}}}\) of 16,400 g/mol. They also claimed that the enzymatic production can be scaled up to the pilot plant level (2.0 tons) without undue problems. Besides, poly(hexamethylene adipate) produced from the enzymatic polymerization possesses a lower acid number, higher degree of crystallinity and super crystalline growth rate compared to the conventional counterparts. Moreover, macrolides catalyzed by lipases showed higher polymerizability compared to smaller ring-sized lactones [216].