# Enzymatic Synthesis of Biobased Polyesters and Polyamides
## 8 Lipase-Catalyzed Synthesis of Sustainable Polyesters and Polyamides from Biobased Monomers
### Glycerol-Based Polyesters  
Glycerol-based aliphatic polyesters can be used as thermosets like shape memory materials; and have found potential applications in biomedical and pharmaceutical fields, for example, they can be used as carriers for drug delivery, sealants or coatings for tissue repair, and agents for antibacterial applications [278]. The N435-catalyzed polymerization of divinyl adipate and glycerol in bulk yielded poly(glycerol adipate) with a \(\overline{M_{\text{w}}}\) and dispersity of up to 10,400 g/mol and 2.3-3.1, respectively (Scheme 39) [279]. MALDI-ToF MS analysis suggested that linear polyesters with hydroxyl substituents were mainly produced and no polymer network was formed. The number of hydroxyl groups per repeating units was around 0.8-0.9; and the pendant groups of the synthetic poly(glycerol adipate) consisted of 90%-95% of secondary and 5%-10% of primary hydroxyl groups. By replacing the activated divinyl adipate with unactivated adip acid, the N435-catalyzed enzymatic polycondensation also resulted in poly(glycerol adipate), with a slight low \(\overline{M_{\text{w}}}\) of 3700 g/mol and a dispersity of 1.4 (Scheme 40) [280]. Poly(glycerol-1,18-_cis_-9-octadecenedioate) was successfully produced via the N435-catalyzed polycondensation of 1,18-_cis_-9-octadecenedioic (oleic diacid) and glycerol in bulk (Scheme 41) [283]. At a molar monomer feed ratio of 1.0:1.0, the \(\overline{M_{\rm n}}\) and dispersity of the obtained polyesters were up to 9100 g/mol, and around 3.3-3.4, respectively. However, the percentage of dendritic glycerol units (Den %) was quite low, around 13%-16%. By increasing the molar feed ratio of oleic diacid and glycerol from 1.0:1.0 to 1.0:1.5, the resulting polyesters possessed a similar \(\overline{M_{\rm n}}\) and dispersity, but a significant higher Den % (\(\sim\)31%). In contrast, gelation was observed in the polymerization catalyzed by dibutyltin oxide. Moreover, several glycerol-based _co_-polyesters were successfully produced via lipase-catalyzed polycondensation. The enzymatic _co_-polymerization of divinyl adipate, glycerol and 1_A_-BDO gave poly(glycerol adipate-_co_-butylene adipate) (Scheme 39) [279]. The hydroxyl number of the obtained _co_-polyesters can be well controlled by adjusting the amount of 1,4-BDO in the reaction mixture. Poly(octamethylene adipate-_co_-glyceryl adipate) were successfully produced via the N435-catalyzed _co_-polymerization of glycerol, adipic acid and 1,8-octanediol in bulk (Scheme 40) [280; 281; 282], with \(\overline{M_{\rm n}}\)'s of up to 75,600 g/mol. The \({}^{13}\)C-NMR study indicated that the obtained polyesters were highly branched but had few interchain cross-links; and the degree of branching and molecular weights can be controlled by altering the reaction time and molar feed ratio of monomers [282]. In addition, due to the regio-selectivity of N435, the enzymatic polymerization gave linear polyesters at short reaction times (\(\leqslant\)18 h) but yielded highly branched polyesters at a long reaction time (42 h). Moreover, with respect to esterifications, N435 showed 77% to 82% of the regio-selectivity towards the primary hydroxyl groups of glycerol and this was independent of the amount of glycerol in the reaction media. The enzymatic _co_-polymerization of divinyl esters, glycerol and \(\omega\)-fatty acids were also investigated, using lipases as biocatalysts (Scheme 42) [284; 285]. Among the tested lipases, N435 showed the highest catalytic activity. The enzymatic polymerization yielded biodegradable cross-linkable polyesters with \(\overline{M_{\rm n}}\)'s of up to 8500 g/mol. The obtained polyesters were thermally cross-linked, which resulted in transparent polymeric films with high-gloss surfaces. Later, the same research group reported the synthesis of epoxide-containing, glycerol-based _co_-polyesters via N435-catalzyed polymerization via two routes (Scheme 43) [286].