A Green Route for the Preparation of Aliphatic Polyesters via Lipase‐catalyzed Prepolymerization and Low‐temperature Postpolymerization

Abstract

Lipase‐catalyzed polycondensation of two biobased diacids, 1,12‐dodecanedioic acid and 1,14‐tetradecanedioic acid, with 1,8‐octanediol was achieved using immobilized Lipase B from Candida antarctica. The procedure resulted in partially renewable prepolymers, while poly(octylene adipate) from petroleum‐based adipic acid was also synthesized for comparison reasons, revealing a dependence of the enzymatic polymerization degree on monomer composition. The prepolymers were further submitted to bulk postpolymerization at temperatures in the vicinity of their melting point under flowing nitrogen. The intrinsic viscosity increase was found up to 12%, with no significant impact on the polyesters thermal properties.

Production of biodegradable polyesters via enzymatic polymerization and solid state finishing

“…15,17,29,41 The herein achieved number-average MWs (M n H-NMR ) were in the range of 3700-8000 g/mol, with PE 4.4A presenting the lower value probably due to lower enzyme affinity with the short chains of the reactants. On the other hand, when comparing 1,8-octanediol-based PEs, 1,14-tetradecanedioic acid resulted in the lowest MW PE, as already shown in our previous work, 40 probably because of its limited purity (97.0% vs. 98.5% for 1,12-dodecanedioic acid) or enzyme's lower selectivity to this monomer.…”

“…For reaction conditions of 75 C, 4 h, 20 mbar (Samples A), the attained yields were in the range of 65%-97%, resulting in PE 4.4, PE 8.10, PE 8.12, and PE 8.14 with intrinsic viscosities of 0.180, 0.261, 0.301, and 0.253 dL/g, respectively. Comparatively, previous experiments in toluene at the same temperature and in the presence of molecular sieves 40 provided PE 8.12 and PE 8.14 with lower [g], i.e., 0.189 and 0.181 dL/g, indicating the higher efficiency of the herein suggested technique with diphenylether and vacuum. This is in accordance with literature because diphenylether has been proven to be the most effective solvent among a variety of substances, e.g., xylene, tetramethylene glycol, 2-methoxyethyl ether, toluene, heptane, 1,4-dioxane, and diisopropyl ether.…”

“…Ester bonds act as defects along the polymer backbone; therefore, for PE 8.10, 8.12, and 8.14, which consist of large macromolecular chains, as the distance between ester groups increase, the number of defects decreases and consequently T m and DH m raise. 40 However, PE 4.4 was excluded from this rule, showing the higher T m , as it was expected. PE 4.4 exhibits balanced performance in thermal and mechanical properties, and its high melting point can be considered a result of its rigid and symmetric short repeating unit.…”

“…4 C. Finally, based on TGA curves, weight loss started at 380 C and lasted up to 480 C, whereas the maximum weight loss was noted at 418 C-420 C (T d ). PE 8.10, however, presented a two-step degradation mechanism, starting at 160 C, a phenomenon that has been reported before for PE 8.6, 40 indicating probably that 1,8-octanediol-based PEs with less than 12 carbon atoms in the corresponding diacid may be less stable than the rest.…”

“…Concerning thermal properties, melting points in the range of 67 C-92 C were reached, with enthalpies of fusion between 77 and 150 J/g (Figure 3), both values being higher compared with the results of previous enzymatic polymerization runs in toluene and in the presence of molecular sieves. 40 Values from Ref. 40 concerning PE 8.6 are also quoted for comparison.…”