Enzymatic synthesis of poly-l-lactide in supercritical R134a

The production of biodegradable and biocompatible poly-l-lactide has been successfully achieved by enzymatic ring-opening polymerization of l-lactide in subcritical and supercritical 1,1,1,2-tetrafluoroethane (scR134a). Best results were obtained in scR134a at 105 °C and 50 bar using the thermostable lipase from Burkholderia cepacia with a maximum PLLA yield above 50%. The media at supercritical conditions using 40% (wt/v) and 10% (wt/wt) loads of monomer and lipase, respectively, showed remarkable increase in polymer molecular weights as compared to other reaction conditions. The synthetized PLLA samples were semi-crystalline, as determined by powder diffraction X-ray analyses, with a maximum percentage of crystallinity of ca. 35%. The physico-chemical characteristics of this green organic compressed fluid, especially its relative polarity and hydrophobicity, enhanced the solubility of the monomer and subsequent polymeric products with sustained lipase activity even above its supercritical point. This route circumvents the toxicological or environmental issues associated to the syntheses of poly-l-lactide using metal catalysts or common organic solvent media.

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► Lipase from Burkholderia cepacia catalyzes ring-opening polymerization l-lactide in compressed 1,1,1,2-tetrafluoroethane media.
► The activity of lipase BC is maintained at the supercritical conditions of 105 °C and 50 bar.
► Compressed R134a media solubilizes l-lactide monomer and partially poly-l-lactide products.
► Supercritical R134a media improved product characteristics compared to subcritical R134a, scCO2 and bulk media.
► Semi-crystalline poly-l-lactide is achieved with up to 35% of crystallinity.