# Enzymatic Synthesis of Biobased Polyesters and Polyamides
## 8 Lipase-Catalyzed Synthesis of Sustainable Polyesters and Polyamides from Biobased Monomers
### Biobased Unsaturated Aliphatic Polyesters  
Currently, the synthesis of biobased unsaturated polyesters, especially itaconate-based unsaturated polyesters, has not been well studied. This is because the sensitive C=C bond can be deteriorated easily under conventional polymerization conditions such as elevated temperatures and metal catalysts. However, this problem can be easily overcome by using enzyme catalysts in the polymerization, due to the mild synthetic conditions and the high catalytic specificity of the enzyme catalysts. However, the lipase-catalyzed direct polycondensation of itaconate and aliphatic diols with short chain length generally resulted in oligomers. As reported by [PERSON] et al., the solvent-free polyesterification of dimethyl itaconate and 1,4-BDO catalyzed by CALB gave a mixture of oligomers from dimer to pentamer [259; 260]. Similarly, the N435-catalyzed polymerization of itaconic anhydride with aliphatic diols (C4-C10) gave oligomers with \(\overline{M_{\mathrm{n}}}\)'s of around 150-390 g/mol, although itaconic anhydride was completely consumed [261]. This is because the enzymatic polycondensation is hampered by the low reactivity of itaconate due to the lower electrophilicity of the acyl carbon (C\({}_{\mathrm{s}}\), Scheme 29) adjacent to the vinyl group [259]. However, the low reactivity of itaconate in enzymatic polymerization could be overcome by optimizing the reaction conditions: (1) improving the mass transfer and the enzyme distribution in the reaction mixture; (2) increasing the enzyme loading; (3) lowering the diol concentration; and (4) choosing more appropriate diols [259]. Indeed, by using glycols with longer chain lengths or with a rigid structure, itaconate-based homo-polyesters with relatively higher molecular weights were obtained from the lipase-catalyzed polycondensation. As reported by [PERSON] et al. [262], the N435-catalyzed polymerization of itaconic acid with 1,4-cyclohexamethanol/poly(ethylene glycol) gave homo-polymers with a \(\overline{M_{\mathrm{w}}}\) of 2600 and 8600 g/mol, respectively. On the contrary, the tin(II) 2-ethylhexanoate-catalyzed polycondensation with itaconic acid gelled within hours. In addition, itaconate-based \(\varco\)-polyesters with high molecular weights can be prepared via lipase-catalyzed \(\varco\)-polymerization, as discussed below. The N435-catalyzed \(\varco\)-polymerization of itaconic acid, adipic acid and 3-methyl-1,5-pentanediol resulted in a \(\varco\)-polymer with a \(\overline{M_{\mathrm{w}}}\) of 19,000 g/mol [262]. Poly(12-hydroxyatearate-\(\varco\)-butylene itaconate) with a \(\overline{M_{\mathrm{w}}}\) of 30,000 g/mol was obtained from the lipase-catalyzed directly polycondensation of methyl 12-hydroxyateate, dimethyl itaconate and 1,4-BDO (Scheme 30) [263]. Moreover, the lipase-catalyzed ring-opening addition-condensation polymerization of methyl 12-hydroxyatearate and cyclic butylene itaconate dimer resulted in poly(12-hydroxyateate-\(\varco\)-butylene itaconate) with a significantly higher \(\overline{M_{\mathrm{w}}}\) of 160,000 g/mol. Furthermore, the NMR study indicated that the enzymatic polymerization catalyzed by different lipases yielded poly(12-hydroxyateate-\(\varco\)-butylene itaconate) with different microstructures. As shown in Scheme 30, no ester bond was formed between the hydroxyl group of 12-hydroxyateate and the carboxyl group of itaconate when the polymerization was catalyzed by N435. However, by using immobilized _Burkholderia cepacia_ lipase (lipase BC), an ester bond was formed between the 12-hydroxyateate and itaconate unit. Recently, we investigated the N435-catalyzed polymerization of fully biobased poly(butylene succinate-_co_-itaconate) (PBSI) (Scheme 31) [264,265]. We found that the enzymatic polycondensation of succininic acid, itaconic acid, and 1,4-butanediol only yielded oligomers, with \(\overline{M_{\mathrm{w}}}\)'s of around 500-1500 g/mol, despite different polymerization methods were used.