Abstract
Reactive extrusion and magnesium (II) N-heterocyclic carbene catalyst are successfully employed in continuous polylactide synthesis. The possibility of using six-membered N-heterocyclic carbene adducts to act as efficient catalysts towards the sustainable synthesis of poly(l-lactide) through ring-opening polymerization of l-lactide (LA) is first investigated in bulk batch reactions. Under optimized solvent-free conditions, polylactide (PLA) of moderate to high molecular weights and excellent optical activities are successfully achieved. These promising results are further applied in the continuous production of PLA in an extruder.
Highlights
IntroductionEnvironmental concerns have pushed both scientists and industries towards the development of sustainable plastics, e.g., materials of an annually renewable origin, obtained via efficient synthetic procedures (low energy consumption and low components of toxicity (if any), solvent consumption, and waste) and biodegradability (or at least recyclability) [1,2]
Environmental concerns have pushed both scientists and industries towards the development of sustainable plastics, e.g., materials of an annually renewable origin, obtained via efficient synthetic procedures (low energy consumption and low components of toxicity, solvent consumption, and waste) and biodegradability [1,2]
Conversion is calculated from Size-exclusion chromatography (SEC) analyses of the crude product, while molecular characteristics are calculated from SEC of the purified polymer
Summary
Environmental concerns have pushed both scientists and industries towards the development of sustainable plastics, e.g., materials of an annually renewable origin, obtained via efficient synthetic procedures (low energy consumption and low components of toxicity (if any), solvent consumption, and waste) and biodegradability (or at least recyclability) [1,2]. A large variety of purely organic and transition metal-free catalysts have been investigated for the last 20 years and found to be efficient in solution [8] Their applicability in bulk, (where the polymerization temperature surpasses 150 ◦ C) remains inadequate due to the significant incidence of undesirable side-reactions such as inter- and intra-molecular transesterification reactions as well as epimerization, yielding PLA-based materials of low crystallinity and poor thermomechanical performances [8,9]. 170 ◦ C, significant efforts have been made on electronic stabilizations through the use of suitable ligands, yielding labile NHC–based adducts [19,20,21,22] Such adducts have shown to be able to liberate active free-carbene in other bulk polymerization systems and maintain their efficiency at high temperatures [8,23]. The transfer of the optimized solvent-free conditions towards the continuous ring-opening polymerization of l,l-lactide (l,l-LA) was performed, and polylactide (PLA) of moderate to high molecular weights and preserved optical activities was successfully produced
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