# Enzymatic Synthesis of Biobased Polyesters and Polyamides
## 8 Lipase-Catalyzed Synthesis of Sustainable Polyesters and Polyamides from Biobased Monomers
### Biobased Furan Polyesters and Furan Polyamides  
Furan polymers are not new polymers. In the late 1970s, poly(hexamethylene furanoate), a furan polyester, was synthesized by [PERSON] and [PERSON] [296, 297]; and various furan polyesters were successfully prepared by [PERSON] et al. [298], [PERSON] et al. [299], and [PERSON] et al. [300] since 1990s. In recent years, the research on FDCA-based polyesters and polyamides is booming, due to the fast development of biobased FDCA and the broad potential applications of FDCA-based polymers [16]. The FDCA-based polymers are promising sustainable aromatic polymer alternatives, and FDCA-based polymers possess similar or even better properties than their petrol-base counterparts. For example, recent studies suggested that poly(ethylene furanoate) (PEF) possesses better barrier properties compared to PET: PEF shows surprisingly large reductions in CO\({}_{2}\) permeability (19\(\times\)), O\({}_{2}\) permeability (11\(\times\)) and diffusivity (31\(\times\)) [301, 302]. At present, FDCA-based polyesters and polyamides are predominately synthesized via melt polycondensation at elevated temperatures of around 200 \({}^{\circ}\)C. However, decarboxylation of FDCA takes place at around 195 \({}^{\circ}\)C and other side-reactions may occur at such elevated temperatures [16, 303, 304, 305], which may lead to the discoloration of the resulting polymers and the formation of low molecular weight products. However, these drawbacks could be circumvented by using enzyme catalysts. The N435-catalyzed polymerization with dimethyl 2,5-furandicarboxylate (dimethyl FDCA)/BHMF/5-hydroxymethyl-2-furancarboxylic acid (HMFA) was reported by [PERSON]. [306] and [PERSON] et al. [307], using a one-stage method in the mixture of toluene and _tert_-butanol. However, only a mixture of linear and cyclic furan oligomers were produced (Scheme 53). Recently, we studied the N435-catalyzed polymerization of BHMF and various diacid ethyl esters, using the two-stage, three step method (Scheme 54) [308]. BHMF-based polyesters with low molecular weights were produced, with \(\overline{M_{\mathrm{w}}}\)'s of around 1800-2900 g/mol. The polymerization kinetic study and MALDI-ToF MS analysis revealed that ether end groups were formed during the enzymatic polymerization, which led to the low molecular weights. FDCA-based furanic-aliphatic polyesters were successfully produced via the enzymatic polymerization of dimethyl FDCA with various aliphatic diols, using a two-stage method in diphenyl! ether at 80-140 \({}^{\circ}\)C (Scheme 55) [309]. The obtained polyesters reached a very high \(\overline{M_{\mathrm{w}}}\) of up to 100,000 g/mol, which is normally hard to achieve by enzymatic polymerization. For the first time we demonstrated that enzymatic polymerizations are capable of producing high molecular weight FDCA-based polyesters, which have been primarily synthesized via step-growth polymerization using organometallic catalysts at elevated temperatures around 150-280 \({}^{\circ}\)C. Moreover, we found that CALB prefers alkane-\(\alpha\),\(\omega\)-aliphatic linear diols of > 3 carbons. Furthermore, the FDCA-based furanic-aliphatic polyesters possess similar crystalline and thermal properties compared to their petrol-based counterparts, semi-aromatic polyesters. Figure 53: N435-catalyzed polymerizations with furan monomers: bis(hydroxymethyl)furan (BHMF), 5-hydroxymethyl-2-furancarboxylic acid (HMFA) and dimethyl 2,5-Furandicarboxylic acid (FDCA) [306,307]. Furthermore, high molecular weight FDCA-based furanic-aliphatic polyamides were produced from the enzymatic polycondensation of dimethyl FDCA and 1,8-ODA, using a one-stage method or a temperature-varied two-stage method (Scheme 56) [310]. The FDCA-based furanic-aliphatic polyamides can be used as a promising sustainable alternatives to petrol-based polyphthalamides (semi-aromatic polyamides) and be applied as thermoplastic engineering polymers and high performance materials.