Reactive Extrusion and Magnesium (II) N-Heterocyclic Carbene Catalyst in Continuous PLA Production

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.

Review: Syntheses of poly(lactic acid)s and their block copolymers for drug delivery applications

“…This said, interesting work, on several levels, has also made possible the continuous production of PLA with carbene‐based catalysts. In the work by Mincheva et al 69 . the ROP with carbene is optimized and then used in continuous production with an extruder in a solvent‐free bulk polymerization.…”

“…Proposed mechanism for N ‐heterocyclic carbene polymerization of lactide with Mg, reproduced from reference 69 by courtesy of MDPI.…”

“…68 This said, interesting work, on several levels, has also made possible the continuous production of PLA with carbene-based catalysts. In the work by Mincheva et al 69 the ROP with carbene is optimized and then used in continuous production with an extruder in a solvent-free bulk polymerization. An additional benefit is that the Nheterocyclic carbene (NHC) was stable enough to prepare under air and could easily be coupled with Mg.…”

Synthesis of Six-Membered N-Heterocyclic Carbene Precursors Based on Camphor

“…Diamines 6a and 6b were isolated with a diastereoselectivity of 99:1 and 90:10, respectively. Finally, cyclic amidinium salts 7a-c were isolated in 65-72% yield by treating diamines 6a and 6b in triethyl orthoformate in the presence of ammonium tetrafluoroborate or ammonium chloride at an elevated temperature [30,31]. The exo-amidinium salts 7a and 7b were isolated in 99:1 dr, while the endo-salt 7c was isolated in 91:9 dr (Scheme 1).…”

Synthesis of potentially biobased poly(hexamethylene sebacate) via reactive extrusion

“…If we come back to polyesters, several studies were published on ringopening polymerization that is fast and well adapted to extrusion [11,12]. For example, the literature describes how to synthesize and modify poly (lactic acid) by extrusion [13,14]. Polycaprolactone is also a good candidate to be polymerized in extruders [15][16][17].…”