A comparison of zwitterionic and anionic mechanisms in the dual-catalytic polymerization of lactide

Balint, Alexander; Naumann, Stefan

doi:10.1039/d1py00992c

Cited by 6 publications

(7 citation statements)

References 45 publications

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“…Previous investigations highlighted that the cocatalysis of NHOs with Lewis acids holds a great potential for the modulation of ROP. ,− ,, Having established that a direct polymerization of MTC-PFP using solely NHO is impossible, we therefore attempted a cocatalyst approach employing the Lewis acid magnesium iodide (MgI 2 ). This specific metal halide has been found to significantly increase polymerization control and to moderate NHO reactivity for lactone conversion .…”

Section: Resultsmentioning

confidence: 99%

Nontoxic N-Heterocyclic Olefin Catalyst Systems for Well-Defined Polymerization of Biocompatible Aliphatic Polycarbonates

et al. 2022

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Herein, N-heterocyclic olefins (NHOs) are utilized as catalysts for the ring-opening polymerization (ROP) of functional aliphatic carbonates. This emerging class of catalysts provides high reactivity and rapid conversion. Aiming for the polymerization of monomers with high side chain functionality, six-membered carbonates derived from 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) served as model compounds. Tuning the reactivity of NHO from predominant side chain transesterification at room temperature toward ring-opening at lowered temperatures (−40 °C) enables controlled ROP. These refined conditions give narrowly distributed polymers of the hydrophobic carbonate 5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one (MTC-OBn) (Đ < 1.30) at (pseudo)first-order kinetic polymerization progression. End group definition of these polymers demonstrated by mass spectrometry underlines the absence of side reactions. For the active ester monomer 5-methyl-5-pentafluorophenyloxycarbonyl-1,3-dioxane-2-one (MTC-PFP) with elevated side chain reactivity, a cocatalysis system consisting of NHO and the Lewis acid magnesium iodide is required to retune the reactivity from side chains toward controlled ROP. Excellent definition of the products (Đ < 1.30) and mass spectrometry data demonstrate the feasibility of this cocatalyst approach, since MTC-PFP has thus far only been polymerized successfully using acidic catalysts with moderate control. The broad feasibility of our findings was further demonstrated by the synthesis of block copolymers for bioapplications and their successful nanoparticular assembly. High tolerability of NHO in vitro with concentrations ranging up to 400 μM (equivalent to 0.056 mg/mL) further emphasize the suitability as a catalyst for the synthesis of bioapplicable materials. The polycarbonate block copolymer mPEG44-b-poly(MTC-OBn) enables physical entrapment of hydrophobic dyes in sub-20 nm micelles, whereas the active ester block copolymer mPEG44-b-poly(MTC-PFP) is postfunctionalizable by covalent dye attachment. Both block copolymers thereby serve as platforms for physical or covalent modification of nanocarriers for drug delivery.

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Section: Resultsmentioning

confidence: 99%

Nontoxic N-Heterocyclic Olefin Catalyst Systems for Well-Defined Polymerization of Biocompatible Aliphatic Polycarbonates

et al. 2022

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“…At present, scenario (i) is accepted as the general route for most Lewis acids, [3][4][5][6][7][8][9][10][11] and is capable of yielding cyclic polymers. 3 However, if scenario (ii) is correct cyclic polymers will not be achieved and an initiation mechanism resembling that of Claisen condensation will occur.…”

Section: Initiation Reaction Mechanismmentioning

confidence: 99%

“…3,4 Zwitterionic ring-opening polymerization of lactones by LPs, is achieved through a Lewis base bound to the ester carbonyl group and is stabilized by a Lewis acid at the alkoxide propagating chain end. [3][4][5][6][7][8][9][10][11] Due to the differences in interacting nature between a LP and the monomer, LPs exhibit large variations in activity, where some LPs show high activity for some monomers, but at the same time are unable to achieve any conversion of others. [12][13][14][15][16][17][18] An example of a monomer considered 'challenging to polymerize' is the macrolactone ω-pentadecalactone (PDL), as it has low ring strain and the polymerization thermodynamics are entropy driven.…”

Section: Introductionmentioning

confidence: 99%

“…5 This makes zwitterionic Lewis pair polymerization kinetically very similar to anionic polymerization, where the initiation by the Lewis base and the strength of the Lewis acid (counter ion) mainly dictates the rate and control over the polymerization. 9 Although a weaker ZnEt 2 Lewis acid accelerates the reaction rate, ZnEt 2 is inherently more prone to side reactions due to a higher basicity of the ethyl anions compared to e.g. the pentafluoro benzene anion.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Linear not cyclic – unravelling an anionic initiation pathway for Lewis pair polymerization of lactones

et al. 2023

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N‐Heterocyclic Carbene‐Based Zinc Complexes: Same Precursors for Different Lactide Ring‐Opening Polymerization Mechanisms.

et al. 2022

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Two zinc complexes bearing NHC ligands were synthesized and fully characterized by NMR spectroscopy. Their behavior in the Ring-Opening Polymerization (ROP) of lactides was investigated under several conditions of reaction. They showed to be efficient initiators, producing polylactides with molecular weights depending on the cocatalysts. Microstructural analysis of poly(rac-LA) by 1 H NMR spectroscopy revealed a slightly enriched-heterotactic PLAs with P r values up to 0.66. Inspection of the kinetic parameters for L-LA and rac-LA allowed to compare the k obs of the studied complexes 1 and 2 under different conditions, and showed that propagations present the usual pseudo-first-order dependence on monomer concentration. Hence, some reactivity studies were carried out, addressed to unravel the nature of the active species in the polymerization processes conducted in the presence of different catalytic systems, namely zinc complexes alone and in combination with neutral or ionic cocatalysts.

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A comparison of zwitterionic and anionic mechanisms in the dual-catalytic polymerization of lactide

Abstract: Using catalyst pairs consisting of N-heteorcyclic olefins (NHOs) and metal-based Lewis acids for the polymerization of lactide, it is possible to precisely control the resulting polymerization mechanism, and NHO placement,...

Cited by 6 publications

References 45 publications

Nontoxic N-Heterocyclic Olefin Catalyst Systems for Well-Defined Polymerization of Biocompatible Aliphatic Polycarbonates

Nontoxic N-Heterocyclic Olefin Catalyst Systems for Well-Defined Polymerization of Biocompatible Aliphatic Polycarbonates

Linear not cyclic – unravelling an anionic initiation pathway for Lewis pair polymerization of lactones

N‐Heterocyclic Carbene‐Based Zinc Complexes: Same Precursors for Different Lactide Ring‐Opening Polymerization Mechanisms.

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