# Enzymatic Synthesis of Biobased Polyesters and Polyamides
## 8 Lipase-Catalyzed Synthesis of Sustainable Polyesters and Polyamides from Biobased Monomers
### Polyesters Derived from Long Chain Fatty Acids and their Derivatives  
Long chain fatty acids may contain one or more C=C bonds within the backbones. The C=C bonds can be further modified to form other functional groups such as epoxy, thiol, and hydroxyl group [153; 266], rendering fatty acid-based polyesters with diverse functionalities. Fatty acid-based polyesters can be used as thermoset resins, coating materials and biomaterials for biomedical applications, and so on [267; 268; 269]. The pioneer work on the enzymatic polymerization with long chain fatty acids was reported by [PERSON] et al. [270]. They investigated the lipase-catalyzed polymerization of ricinoleic acid/methyl ricinoleate in bulk (Scheme 33). Among the tested lipases, immobilized lipase PC showed the highest reactivity towards ricinoleic acid and methyl ricinoleate. The enzymatic polymerization with ricinoleic acid resulted in polyricinoleate with a \(\overline{M_{\mathrm{w}}}\) of up to 8500 g/mol. However, by replacing ricinoleic acid with methyl ricinoleate, polyricinoleate with a much higher \(\overline{M_{\mathrm{w}}}\) of up to 100,600 g/mol were produced. Later, the N435-catalyzed synthesis of poly(12-hydroxydodecanoate-_co_-12-hydroxystearate) was studied by the same research group (Scheme 34) [271]. The \(\overline{M_{\mathrm{w}}}\), dispersity and reaction yield of the resulting _co_-polyesters were around 92,300-118,200 g/mol, 2.8-3.3, and 83%-88%, respectively. In addition, the molar percentage of 12-hydroxydodecanoate units in the final products can be tailored from 0% to 100% by adjusting the feed ratio. **Scheme 34. ** N435-catalyzed polycondensation of 12-hydroxydodecanoic acid and methyl 12-hydroxystearate [271]. Biobased functional polyesters can be produced via enzymtic polymerization with unsaturated or epoxidized \(\alpha\),\(\omega\)-carboxylic fatty acid derivatives [272; 273]. The long chain unsaturated and epoxidized \(\omega\)-carboxy fatty acid derivatives can be synthesized via chemical [272] or biocatalytic approaches [273]. The N435-catalyzed polycondensation of unsaturated or epoxidized \(\omega\)-carboxy fatty acid methyl esters (C18, C20 and C26) with alkane-\(\alpha\),\(\omega\)-aliphatic diols (C3 and C4) resulted in polyesters with \(\overline{M_{w}}\)'s, dispersities and reaction yields of up to 11,600 g/mol, 1.2-2.6, and 49%-84%, respectively (Scheme 35) [272]. In addition, the two-step biocatalytic approach gave biobased functional polyesters with \(\overline{M_{w}}\)'s and dispersities of around 25,000-76,000 g/mol, and around 2.0-3.1, respectively (Scheme 36) [273]. **Scheme 35. ** N435-catalyzed polycondensation of unsaturated or epoxidized \(\omega\)-carboxy fatty acid methyl esters with alkane-\(\alpha\),\(\omega\)-aliphatic diols [272]. **Scheme 36. ** A two-step biocatalytic synthesis of biobased functional polyesters from \(\omega\)-carboxy fatty acids and diols [273]. On the other hand, cutin and suberin are lipophilic macromolecules which are natural substances found in cell walls of higher plants as structural components. Cutin covers all the aerial surfaces of plants in the plant cuticle, while suberin is the main constituent of cork cells. Their fatty acid derivatives, such as long chain \(\omega\)-hydroxyalkanoic acids, and \(\alpha\),\(\omega\)-alkanedio acids, and substituted \(\omega\)-hydroxyalkanoic acids, are attractive biobased monomers for the synthesis of functional aliphatic polyesters [152,274]. [PERSON] et al. [275] did pioneer work on the enzymatic synthesis of suberin-based polyesters (Scheme 37). The N435-catalyzed polymerization with _cis-_9,10-epoxy-18-hydroxyoctadecanoic acid in toluene resulted in epoxy-functionalized polyesters with the highest molecular weights. The \(\overline{M_{\mathrm{w}}}\) and dispersity were 20,000 g/mol, and 2.2, respectively.