Ring-opening Polymerization Of Lactide Research Articles

Stereoselectivity Control Interplay in Racemic Lactide Polymerization by Achiral Al-Salen Complexes.

The origin of stereocontrol in ring opening polymerization (ROP) of racemic lactide (rac-LA) promoted by achiral aluminium-based catalysts has been explained through DFT calculations combined with a molecular descriptor (%VBur) and the activation strain model (ASM-NEDA) analysis. The proposed chain end control (CEC) model suggests that the ligand framework adopts a chiral configuration mimicking the enantiomorphic site control (ESC) while also incorporating control of the last inserted monomer unit. It is found that the ligand wrapping mode around the aluminium centre is dictated by the monomer configuration (R,R-LA and S,S-LA). A good correlation with experimental data is achieved only when accounting for the ligand dynamic features and its steric influences, as highlighted by %VBur steric maps and ASM-NEDA analysis. Understanding the ESC and CEC interplay is an important target for obtaining stereoselective ROP polymerization for the synthesis of biodegradable materials with tailored properties.

Intensive Cycloalkyl-Fused Pyridines for Aminopyridyl-Zinc-Heteroimidazoles Achieving High Efficiency toward the Ring-Opening Polymerization of Lactides.

The model precatalyst sp3- and sp2-N dinitrogen-coordinated zinc-heteroimidazole has been used as an efficient catalyst for the ring-opening polymerization of cyclic esters. Subsequent to our exceptional active 5,6,7-trihydroquinolin-8-amine-zinc catalysts for the ring-opening polymerization (ROP) of ε-caprolactone, various pyridine-fused cycloalkanones (ring size from five to eight) are developed for the correspondent fused amine-pyridine derivatives and their zinc-heteroimidazole chloride complexes Zn1-Zn8 (LZnCl2) bearing N-diphenylphosphinoethyl pendants. Activated with two equivalents of LiN(SiMe3)2, the title zinc complexes efficiently promote the ROP of L-lactide (L-LA) in situ; among them, Zn4/2Li(NSiMe3)2 catalyzed 500 equivalent L-LA at 80 °C with 92% conversion in 5 min (TOF: 5520 h-1). Under the same conditions, the catalytic efficiency for the ROP of rac-LA by Zn1-Zn8/2Li(NSiMe3)2 was slightly lower than that for L-LA (highest TOF: 4440 h-1). In both cases, cyclooctyl-fused pyridyl-zinc complexes exhibited higher activity than others, while the cycloheptyl-fused zinc complexes showed the lowest activity. The microstructure analysis of the polymers showed they possessed a linear structure capped with CH3O as major and cyclic structure as minor. In this work, all the ligands and zinc complexes were well characterized by 1H/13C/31P NMR, FT-IR spectroscopy as well as elemental analysis.

Ring-opening polymerization of lactide catalyzed using metal-coordinated enzyme-like amino acid assemblies.

Polylactide (PLA), a biocompatible and biodegradable polymer, is widely used in diverse biomedical applications. However, the industry standard for converting lactide into PLA involves toxic tin (Sn)-based catalysts. To mitigate the use of these harmful catalysts, other environmentally benign metal-containing agents for efficient lactide polymerization have been studied, but these alternatives are hindered by complex synthesis processes, reactivity issues, and selectivity limitations. To overcome these shortcomings, we explored the catalytic activity of Cu-(Phe)2 and Zn-(Phe)2 metal-amino acid co-assemblies as potential catalysts of the ring-opening polymerization (ROP) of lactide into PLA. Catalytic activity of the assemblies was monitored at different temperatures and solvents using 1H-NMR spectroscopy to determine the catalytic parameters. Notably, Zn-(Phe)2 achieved >99% conversion of lactide to PLA within 12 h in toluene under reflux conditions and was found to have first-order kinetics, whereas Cu-(Phe)2 exhibited significantly lower catalytic activity. Following Zn-(Phe)2-mediated catalysis, the resulting PLA had an average molecular weight of 128 kDa and a dispersity index of 1.25 as determined by gel permeation chromatography. Taken together, our minimalistic approach expands the realm of metal-amino acid-based supramolecular catalytic nanomaterials useful in the ROP of lactide. This advancement shows promise for the future design of simplified biocatalysts in both industrial and biomedical applications.

Flexible PLA Copolymers with Low Melt Flow Index for Blown Film Applications

AbstractA series of strategies are investigated, which allow internally plasticized polylactide (PLA)‐polyether block copolymers to be effectively melt‐processed through blown film extrusion in the semi‐technical scale. Among the strategies presented are the use of tris(nonylphenyl) phosphite (TNPP) as a chain extender during the ring opening polymerization (ROP) of lactide and the application of ε‐caprolactone (CL) as a plasticizing comonomer. The produced films have a significantly higher flexibility than pure PLA films and are in a comparable range to the flexibility of fossil‐based, film‐grade low‐density polyethylene (LDPE) films.

Self-switchable terpolymerization of cyclic anhydrides, epoxides and lactide catalyzed by C2v-symmetric cobaltoporphyrins

The urgency for biodegradable plastics free from crude oil-based chemicals is currently paramount. These materials should be easily recyclable and capable of undergoing degradation at the end of their useful life. Herein, a series of C2v-symmetric cobaltoporphyrins featuring different substituents were synthesized, and evaluated for their catalytic performance in the self-switchable terpolymerization of epoxides, cyclic anhydrides and lactide in coordination with a co-catalyst bis(triphenylphosphoranylidene) ammonium chloride (PPNCl), under initiator-free conditions. These cobaltoporphyrin homogeneous catalysts exhibit promising chemical selectivity in the multicomponent copolymerization, resulting in kinetic differentiation between the ring-opening copolymerization of epoxides with cyclic anhydrides and the ring-opening polymerization of lactide. Lactide only participates in polymerization after complete conversion of cyclic anhydrides, leading to sequence-regulated block copolyesters. The substituents on the porphyrin ligand have significant influence on its catalytic activity. Among all catalysts tested, DOMePP-CoCl exhibited the most outstanding reactivity under optimal conditions. Furthermore, by utilizing different cyclic anhydrides and epoxide monomers, the DOMePP-CoCl/PPNCl catalytic system still exhibited excellent reaction activity, allowing for the high-yielding and high-selectivity transformation into corresponding multiblock copolyesters.

Interpretable machining learning assisted insights into bifunctional squaramide catalyzed ring-opening polymerization of lactide

A bifunctional squaramide catalyst with tunable activity enables the controlled ring-opening polymerization of lactide. Combining bench experiments and interpretable machine learning offer insights into catalyst structures, promoting catalyst design.

MICROWAVE ASSISTED LACTIDE-GLYCOLIDE HOMO AND COPOLYMERIZATION INITIATED BY MAGNESIUM LACTATE

In this work, microwave-assisted ring opening polymerization (ROP) of lactide (LA) and glycolide (GA) initiated by magnesium lactate was investigated. The influence of microwave power, temperature, and reaction time on homopolymers and copolymer’s structure and thermal properties is discussed. Polymerization of L-lactide (LLA) initiated by the magnesium compound resulted in yields up to 78% and poly(L-lactic acid) (PLLA) with average molar mass of up to 30,600 g mol-1. Homopolymerization of glycolide generate poly(glycolic acid) (PGA) in yields up to 90% and in L-lactide/glycolide copolymerizations yields between 34-82%. PLLA prepared with the initiator presented microstructure with significant amount of stereo errors as the result of a racemization process during polymerization as well as low glass transition temperature (Tg) and melting temperature (Tm), while the PGAs presented high Tg, due to high crystallinity, and Tm in accordance with the literature. LLA and GA copolymerization result in poly(lactic acid-co-glycolic acid) (PLGA) with composition close to polymerization feed composition.

Bis-thiourea and macrocyclic polyamines as binary organocatalysts for the ROP of lactide

New binary catalysts formed by a bis-thiourea and a series of flexible polyaza-macrocycles are revealed to be efficient catalysts for the ring opening polymerization (ROP) of l-lactide.

The metal role on the activity and stereoselectivity of ring opening polymerization of racemic lactide promoted by Salen catalysts

The stereoselective rac-lactide ring opening polymerization (ROP) promoted by enantiopure Salen catalysts has been studied by Density Functional Theory calculations with the aim of understanding the role of the metal atom in both the stereoselectivity and the activity of the process. The results obtained with M = Al, Sc, Y, La were compared to identify the steric and electronic effects deriving from the metal centre by combining a molecular descriptor based on the buried volume percentage (%VBur) and calculations of electronic parameters, including chemical hardness and electrophilicity. Our analysis gave insight into the parameters affecting the outcome of the ROP and we concluded that steric and electronic effects promoting stereoselective polymerization suppress catalyst activity and viceversa.

Synthesis of L-Ornithine- and L-Glutamine-Linked PLGAs as Biodegradable Polymers.

L-ornithine and L-glutamine are amino acids used for ammonia and nitrogen transport in the human body. Novel biodegradable synthetic poly(lactic-co-glycolic acid) derivatives were synthesized via conjugation with L-ornithine or L-glutamine, which were selected due to their biological importance. L-ornithine or L-glutamine was integrated into a PLGA polymer with EDC coupling reactions as a structure developer after the synthesis of PLGA via the polycondensation and ring-opening polymerization of lactide and glycolide. The chemical, thermal, and degradation property-structure relationships of PLGA, PLGA-L-ornithine, and PLGA-L-glutamine were identified. The conjugation between PLGA and the amino acid was confirmed through observation of an increase in the number of carbonyl carbons in the range of 170-160 ppm in the 13C NMR spectrum and the signal of the amide carbonyl vibration at about 1698 cm-1 in the FTIR spectrum. The developed PLGA-L-ornithine and PLGA-L-glutamine derivatives were thermally stable and energetic materials. In addition, PLGA-L-ornithine and PLGA-L-glutamine, with their unique hydrophilic properties, had faster degradation times than PLGA in terms of surface-type erosion, which covers their requirements. L-ornithine- and L-glutamine-linked PLGAs are potential candidates for development into biodegradable PLGA-derived biopolymers that can be used as raw materials for biomaterials.

Understanding catalytic synergy in dinuclear polymerization catalysts for sustainable polymers

Understanding the chemistry underpinning intermetallic synergy and the discovery of generally applicable structure-performances relationships are major challenges in catalysis. Additionally, high-performance catalysts using earth-abundant, non-toxic and inexpensive elements must be prioritised. Here, a series of heterodinuclear catalysts of the form Co(III)M(I/II), where M(I/II) = Na(I), K(I), Ca(II), Sr(II), Ba(II) are evaluated for three different polymerizations, by assessment of rate constants, turn over frequencies, polymer selectivity and control. This allows for comparisons of performances both within and between catalysts containing Group I and II metals for CO2/propene oxide ring-opening copolymerization (ROCOP), propene oxide/phthalic anhydride ROCOP and lactide ring-opening polymerization (ROP). The data reveal new structure-performance correlations that apply across all the different polymerizations: catalysts featuring s-block metals of lower Lewis acidity show higher rates and selectivity. The epoxide/heterocumulene ROCOPs both show exponential activity increases (vs. Lewis acidity, measured by the pKa of [M(OH2)m]n+), whilst the lactide ROP activity and CO2/epoxide selectivity show linear increases. Such clear structure-activity/selectivity correlations are very unusual, yet are fully rationalised by the polymerization mechanisms and the chemistry of the catalytic intermediates. The general applicability across three different polymerizations is significant for future exploitation of catalytic synergy and provides a framework to improve other catalysts.

Bayesian-optimization-assisted discovery of stereoselective aluminum complexes for ring-opening polymerization of racemic lactide

Stereoselective ring-opening polymerization catalysts are used to produce degradable stereoregular poly(lactic acids) with thermal and mechanical properties that are superior to those of atactic polymers. However, the process of discovering highly stereoselective catalysts is still largely empirical. We aim to develop an integrated computational and experimental framework for efficient, predictive catalyst selection and optimization. As a proof of principle, we have developed a Bayesian optimization workflow on a subset of literature results for stereoselective lactide ring-opening polymerization, and using the algorithm, we identify multiple new Al complexes that catalyze either isoselective or heteroselective polymerization. In addition, feature attribution analysis uncovers mechanistically meaningful ligand descriptors, such as percent buried volume (%Vbur) and the highest occupied molecular orbital energy (EHOMO), that can access quantitative and predictive models for catalyst development.

Poly(Lactic Acid) Composites with Lignin and Nanolignin Synthesized by In Situ Reactive Processing.

Poly(lactic acid) (PLA) composites with 0.5 wt% lignin or nanolignin were prepared with two different techniques: (a) conventional melt-mixing and (b) in situ Ring Opening Polymerization (ROP) by reactive processing. The ROP process was monitored by measuring the torque. The composites were synthesized rapidly using reactive processing that took under 20 min. When the catalyst amount was doubled, the reaction time was reduced to under 15 min. The dispersion, thermal transitions, mechanical properties, antioxidant activity, and optical properties of the resulting PLA-based composites were evaluated with SEM, DSC, nanoindentation, DPPH assay, and DRS spectroscopy. All reactive processing-prepared composites were characterized by means of SEM, GPC, and NMR to assess their morphology, molecular weight, and free lactide content. The benefits of the size reduction of lignin and the use of in situ ROP by reactive processing were demonstrated, as the reactive processing-produced nanolignin-containing composites had superior crystallization, mechanical, and antioxidant properties. These improvements were attributed to the participation of nanolignin in the ROP of lactide as a macroinitiator, resulting in PLA-grafted nanolignin particles that improved its dispersion.

Synthesis and Structure‐Driven Acid‐Catalyzed Degradation of Benzoic Cyclic Acetal‐Labeled PEG Precursors toward Shell‐Sheddable PLA Block Copolymer Synthesis

AbstractThe synthesis of acid‐degradable poly(ethylene glycol) (PEG) precursors labeled with benzoic cyclic acetal (BzCA) is reported. To get an insight into their acid‐catalyzed hydrolysis, three precursors are designed with spacers exhibiting different inductive effects between PEG and BzCA linkage. The 1H‐NMR analysis confirms the order of increasing acid‐catalyzed hydrolysis to be ether > ester oxygen > ester carbonyl, which can be attributed to their ability to stabilize benzylic carbocation intermediates formed during hydrolysis. The formed precursors tend to be stable under a tin‐catalyzed condition for ring opening polymerization of lactide (LA), thus enabling the synthesis of well‐controlled acid‐degradable PEG‐based PLA block copolymers labeled with BzCA linkage at the block junction. When being exposed to acidic pH, the copolymers degrade through the cleavage of the junction BzCA linkages. These results guide the design principle of acid‐degradable shell‐sheddable BzCA‐bearing block copolymers for control over their acid‐catalyzed degradation and potentially drug release kinetics.

Stereoselective ring‐opening polymerization ofrac‐lactide catalyzed by phenyl diphosphazene/urea binary catalytic system

AbstractPolylactide (PLA) is a fully bio‐derived polyester with great biodegradability, biocompatibility, and mechanical properties. Synthesis of stereoregular PLA by highly stereoselective organocatalyzed ring opening polymerization (ROP) of racemic lactide (rac‐LA) at room temperature is challenging despite some important developments in the past few years. In this contribution, two bulky phenyl diphosphazene bases,p‐PDPBandm‐PDPB,were conveniently synthesized by the Staudinger reaction. In combination with different hydrogen‐bond donors such as ureas and squaramides, they could mediate the stereocontrolled ROP ofrac‐LA in THF at room temperature. Semicrystalline PLAs with narrow dispersity and high tacticity (Pmup to 0.84) were successfully synthesized in a well‐controlled manner using phenyl diphosphazene based/urea binary catalytic system. Structural analysis verified the linear structure and high end‐group fidelity of the resulting polymers. Moreover, the minimal transesterification of the polymer backbone proved by the MALDI‐TOF MS analysis indicated the good controllability of the phenyl diphosphazene based binary catalytic system.

Metal-free organic catalyst for synthesis of low dispersity poly(ethylene glycol-block-polylactide) copolymers with well-defined structure

Ring-opening polymerization of lactide was performed in the presence of 1,8-diazabicyclo[5.4.0]undec-5-ene as an organic catalyst and polyethylene glycol as a hydroxyl-containing macroinitiator. A series of amphiphilic poly(ethylene glycol-block-polylactide) copolymers with a low dispersity (PDI = 1.1), different stereoregularity and length of the polylactide block was obtained. Nanoparticles with a diameter of 20–25 nm were produced from selected polymers and were studied by in vitro cytotoxicity tests.

Structural Effect of Organic Catalytic Pairs Based on Chiral Amino(thio)ureas and Phosphazene Bases for the Isoselective Ring-Opening Polymerization of Racemic Lactide

Structural Effect of Organic Catalytic Pairs Based on Chiral Amino(thio)ureas and Phosphazene Bases for the Isoselective Ring-Opening Polymerization of Racemic Lactide

Fabrication of PLCL Block Polymer with Tunable Structure and Properties for Biomedical Application.

Biodegradable materials are pivotal in the biomedical field, where how to precisely control their structure and performance is critical for their translational application. In this study, poly(L-lactide-b-ε-caprolactone) block copolymers (bPLCL) with well-defined segment structure are obtained by a first synthesis of poly(ε-caprolactone)soft block, followed by ring opening polymerization of lactide to form poly(L-lactideacid) hard block. The pre-polymerization allows for fabrication of bPLCL with the definite compositions of soft/hard segment while preserving the individual segment of their special soft or hard segment. These priorities make the bPLCL afford biodegradable polymer with better mechanical and biodegradable controllability than the random poly(L-lactide-co-ε-caprolactone) (rPLCL) synthesized via traditional one-pot polymerization. 10 mol% ε-caprolactone introduction can result in a formation of an elastic polymer with elongation at break of 286.15% ± 55.23%. Also, bPLCL preserves the unique crystalline structure of the soft andhard segments to present a more sustainable biodegradability than the rPLCL. The combinative merits make the pre-polymerization technique a promising strategy for a scalable production of PLCL materials for potential biomedical application.

Ring-opening polymerization of lactides and ε-caprolactone catalyzed by Zn(II) aryl carboxylate complexes supported by 4-pyridinyl schiff base ligands

Synthesis and catalytic studies of aryl carboxylate Zn (II) complexes is reported. Reaction of substituted (E)-N-phenyl-1-(pyridin-4-yl)methanimine with a methanolic solution of Zn(CH3COO)2 and substituted aryl carboxylate co-ligands gave heteroleptic Zn(II) complexes; [Zn(C6H5COO)2(L1)]2 (1), [Zn(C7H7COO)2(L1)]2 (2), [Zn (4-F-C6H4COO)2(L1)]2 (3), [Zn(C6H5COO)2(L2)]2 (4), [Zn(C7H7COO)2(L2)]2 (5), [Zn (4-F-C6H4COO)2(L2)]2 (6), [Zn(C6H5COO)2(L3)]2 (7), [Zn(C7H7COO)2(L3)]2 (8), [Zn (4-F-C6H4COO)2(L3)]2 (9). The molecular structures of complexes 1 and 4 are dinuclear with the zinc atom in complex 1 adopting a distorted trigonal bipyramidal geometry in a bi-metallacycle while complex 4 is square pyramidal where all four benzoate ligands bridge the zinc metals in a paddle wheel arrangement. All complexes successfully initiated mass/bulk ring-opening polymerization (ROP) of ϵ-caprolactone (ϵ-CL) and lactides (LAs) monomers with or without alcohol co-initiators at elevated temperatures. Complexes 1, 4 and 6 containing the unsubstituted benzoate co-ligands were the most active in their triad; with complex 4 being the most active (kapp) of 0.3450 h−1. The physicochemical properties of the polymerization products of l-lactide and rac-lactide in toluene revealed melting temperatures (Tm) between 116.58 °C and 188.03 °C, and decomposition temperatures between 278.78 °C and 331.32 °C suggestive of an isotactic PLA with a metal capped end.

Taking the Next Step—Model‐Based Analysis of Robust and Non‐Toxic Zn Catalysts for the Ring Opening Polymerization of Lactide in the Polymer Melt (Adv. Sustainable Syst. 2/2023)

Ring Opening Polymerization In article 2200359, Sonja Herres-Pawlis, Andreas Jupke, and co-workers show that the transition of new non-toxic catalysts for the lactide ring opening polymerization from lab scale to industry is a highly complex process. Hence, promising catalysts end up in the valley of death between these scales. Model-based analysis can bridge this gap, giving an in-depth understanding of these catalysts and pave the way to substitute toxic tin octanoate in industry.